Investigation of leeway and drift for Ovatek life rafts

Transcription

INVESTIGATION OF LEEWAY AND DRIFT
FOR OVATEK LIFE RAFTS
PROJECT FINAL REPORT
Submitted to:
Canadian Coast Guard
Newfoundland Region
St. John’s, Newfoundland
Prepared by:
85 Lemarchant Road
St. John’s, Newfoundland
A1C 2H1
Telephone: 709-753-5788
Facsimile: 709-753-3301
E-mail: oceans@oceans.nf.net
March 2006
The contents of this document reflect the views of OCEANS Ltd. and are not necessarily the
official view, opinion or policy of the Canadian Coast Guard.
OCEANS LTD. PROJECT TEAM:
R. Fitzgerald
D. Finlayson
A. Cook
Project Manager
Project Analyst
Project Engineer
and others
ii
ACKNOWLEDGEMENTS
It is a pleasure to acknowledge the interest and support of the National SAR Program, National
SAR Secretariat, Canadian Coast Guard, and United States Coast Guard. We thank the Canadian
Coast Guard, Newfoundland Region, for making available the CCGS "Harp" and “Ann Harvey”
for use during field trials. There were a number of individuals and groups at the CCG base in St.
John’s that helped us to complete this project. In particular we would like to thank Brian Stone,
Regional Superintendent, Maritime Search and Rescue for his interest, cooperation and support
during all phases of the project. Grant Ivey proved to be an integral part of this project and we
appreciate his day-to-day help and logistical support throughout the project. As well we
appreciate the interest and assistance of Neil Peet, Peter Fontaine, and Dan Frampton. Also,
Steve Sheppard and Kevin Lawless provided us with a great deal of help around the CCG Base.
Thanks also go to the Ship’s Electronic Workshop group from the CCG base for helping with the
installation of equipment onboard the “Ann Harvey”. The Marine Rescue Sub-Centre also
assisted us during our field trials and we would like to thank them for their co-operation. Finally,
we would like to thank Janice Brasier of the Canadian Coast Guard in Ottawa for her help and
support during the project.
We gratefully acknowledge the continued advice and support given by Dr. Arthur Allan of the
United States Coast Guard Research and Development Center, Groton, Connecticut. As well, we
thank Chris Turner of the USCG R&D center for his support during the field program. We also
worked closely with the personnel from the USCG contractor SAIC during the 2005 field trials.
We appreciate their interest in our work and hope their stay in Newfoundland was enjoyable.
Special thanks go to SAIC’s field crew: John Morris, Tom Waddington, Pamela Leuy, Kate
Montgomery, and Jim Singer.
We wish to acknowledge and emphasize the individuals who contributed to the safe and
successful completion of our field programs. In particular, we would like to thank Captain Mike
O’Brien, Chief Officer John Matchum, and the remaining officers and crew of the CCGS “Harp”
for their work during the Phase I field trials. As well, we thank Captain Jim Gurney, Captain Guy
Durnford, First Officer Guy Vanderwaeren, First Officer Wayne Rice, and the remaining officers
and crew of the CCGS “Ann Harvey” for their work during the Phase II field trials. Their
dedication, interest and total cooperation was invaluable in making the field programs a success.
iii
EXECUTIVE SUMMARY
This document is the final report on a two-phase project that was conducted by OCEANS Ltd.
during fiscal years 2004/2005 and 2005/2006 to investigate the Leeway and Drift of Ovatek Life
Rafts on behalf of the Canadian Coast Guard. Primary funding for the project was provided by
the National SAR Secretariat. In-kind support was provided by OCEANS Ltd., the Canadian
Coast Guard and the United States Coast Guard.
Background
In recent years Ovatek Inc., based in New Brunswick, has developed and marketed a new type of
life raft, the 4-person and 7-person Ovatek rigid life raft. These life rafts have been approved by
SOLAS, the Canadian Coast Guard and the United States Coast Guard. These life rafts have
become a popular alternative to the inflatable life raft on board fishing vessels in Atlantic Canada
and the west coast of North America.
An incident involving an Ovatek life raft precipitated the need for leeway data for these life rafts.
In the spring of 2003 a SAR operation was conducted for a 7-person Ovatek life raft in the Gulf
of St. Lawrence. The life raft belonged to the MV “Caboteur” that sank on April 4, 2003 at 1215
EST. Fortunately, in this case, a vessel was standing close by when the ship sank and the 6-man
crew was recovered from the life raft within an hour with no injuries. The life raft and the
Caboteur’s EPIRB were recovered 2 days later on April 6, 2003. However, the incident report
noted that the position of the search objects was very different than the positions calculated by
CANSARP. Further, it stated that upon examination of the incident it is evident that the Ovatek
life raft did not have the same “rhythm of drift” as a conventional life raft. In an effort to
improve the accuracy of CANSARP predictions, a leeway study was proposed and conducted on
4-person and 7-person Ovatek life rafts. Details of this work are discussed in body of this report.
The National SAR Manual (DFO, 1998) defines “leeway” as the “movement of the search object
through water caused by the action of wind on the exposed surfaces of the object”. In this
investigation, consistent with other recent leeway studies (Fitzgerald et al., 1994; Allen and
Plourde, 1999), leeway is defined as:
“Leeway is the velocity vector of the SAR object relative to the downwind
direction at the search object as it moves relative to the surface current as
iv
measured between 0.3 and 1.0 m depth caused by the winds (adjusted to a
reference height of 10 m) and waves.”
In the late 1980’s to mid 1990’s OCEANS Ltd. personnel, with support from the Canadian Coast
Guard, the Transportation Development Centre and the United States Coast Guard conducted a
number of leeway experiments for common SAR objects in environmental conditions typically
encountered on the east coast of Canada. The objects tested in these earlier studies included:
-
4, 6, and 20-person inflatable life rafts
small open plank boats
22-person SOLAS approved fibreglass life capsule
46-person L1011 passenger slide / life raft
an air deployable Sea Rescue Kit consisting of three 6-person life rafts and two survival
packs
The results of these studies have been incorporated in the National SAR Manual and into
CANSARP.
Overall Project Objectives
There was a primary and secondary objective identified for this project with each phase of the
project having specific objectives.
The primary objective of this project was to determine a functional relationship between wind
velocity and leeway speed and angle for 4-person and 7-person Ovatek rigid life rafts in
operationally limiting configurations (1 person on board without a sea anchor deployed and 4 or
7 persons onboard with a sea anchor deployed) for inclusion in the National SAR Manual (DFO,
1998) and CANSARP.
The secondary objective of this project was to investigate improved analysis methodologies for
obtaining SAR object leeway angles off the downwind direction with the goal of increasing the
precision of leeway angle divergence and, ultimately, reducing search area, search time, and
SAR resource requirements
v
Phase I Objectives
There were two main objectives for Phase I and these included:
1. Collect and analyze preliminary field data for determining the leeway for the 4- and 7-person
Ovatek life rafts in wind speeds up to 25 knots.
2. In preparation for the Phase II trials, Phase I was to serve as a test of equipment,
deployment/recovery procedures, scientific instrumentation, and communications.
Phase II Objectives
The main objective of Phase II was to:
1. Collect and analyze field data for determining the leeway for the 4- and 7-person Ovatek life
rafts in wind speeds up to 50 knots
Conclusions
The conclusions in this report are based on a total of 485.7 hours of leeway and drift data that
was collected for the 4- and 7- person Ovatek life rafts during this two-phase project.
The results of the leeway analyses to determine the leeway characteristics of the Ovatek life rafts
have been presented in two forms in this report (see section 4). In the first form linear regression
models have been developed for leeway speed while descriptive statistics are provided for
leeway angle divergence. This is the form currently used by the Canadian Coast Guard. The
leeway characteristics of SAR objects may also be presented in the form of downwind and
crosswind leeway components. This method is presently employed by the USCG and has the
advantage that the downwind and crosswind statistical models used in combination provide
complete information about the SAR object leeway vector, and include a measure of the scatter
about the regression models in the form of standard error statistics.
In summary, there is sufficient confidence in the results to state the following general
conclusions about the leeway characteristics of the Ovatek life rafts.
vi
For lightly-loaded Ovatek life rafts deployed without a drogue:
1. Leeway rates and downwind leeway rates are sufficiently similar, at approximately 3.9
percent of the 10 m wind speed, that the data can been combined to provide linear models
that are representative for the two life raft sizes.
2. Leeway angle divergence characteristics of the 4- and 7-person life rafts are markedly
different; as a consequence, leeway angle statistics and crosswind leeway components
models have been developed for each size of life raft.
For fully-loaded Ovatek life rafts deployed with a drogue:
1. The controlling influence of the drogue is sufficiently strong that the leeway data may be
combined to generate leeway speed models, leeway angle statistics, and downwind and
crosswind leeway velocity component models, that are representative for both sizes of life
raft.
2. For this configuration, leeway rates are approximately 1.0 percent of the 10 m wind speed.
Full details of the leeway models and statistics are given in Table 4-1 through Table 4-6 in this
report. The models are expected to be valid for 10 m wind speeds up to storm force winds of 50
knots
Recommendations
The following are recommendation stemming from the findings of the Ovatek leeway and drift
project.
1. Leeway Speeds and Angles
It is recommended that the Canadian Coast Guard, when planning SAR missions in wind speeds
up to 50 knots for 4- and/or 7-person Ovatek life rafts, use the leeway models shown in Table
4-1 through Table 4-6.
vii
2. Leeway Model Validation
It is recommended as a follow up to the collection of leeway data for the 4- and 7- person Ovatek
life rafts that a validation of the derived leeway models be carried out. The purpose of the
validation would be (1) to confirm the reliability of the leeway models recommended in this
report and (2) demonstrate, by using reliable leeway models based on field research, the
improvement that can be obtained in SAR performance as it relates to finding a SAR object
faster and thus increasing the chances of saving lives which is the real goal of this research.
3. Conduct Probability of Detection (POD) Trials for Ovatek Life Rafts
It is recommended that a Probability of Detection Exercise be carried for 4- and 7-person Ovatek
life rafts. This work would be a logical extension in completing the collection of SAR data for
the 4- and 7-person Ovatek life raft. It is recommended that the data be collected by an all
weather SAR vessel during poor weather which is the more common scenario when there is a
marine emergency on Canada’s East Coast.
Note: Recommendations 2 and 3 could be carried out in parallel.
4. Modify the Rode for Sea Anchor on the Ovatek Life Raft
It is recommended that the rode for the sea anchors presently being used with the Ovatek 4- and
7-person Ovatek life raft be modified to reduce the effects of the dynamic loading on the rode.
Observations made during the Phase I and II field trials first of all showed that this sea anchor is
very efficient. However, it was noticed that the rode of the sea anchor after only a 24 hour
period, in relatively light sea conditions, had begun to fray. It was felt that the constant tugging
of the rode against the rigid hull of the Ovatek life rafts would eventually lead to rode failure.
5. Determine the Leeway of Fully Loaded Ovatek Life Rafts without a Sea Anchor
It is recommended that a short project be carried out to determine the leeway characteristics of
fully loaded 4- and 7-person life rafts without a sea anchor deployed. The sea anchor has to be
attached and deployed by the persons in the life raft. Depending on the evacuation
circumstances this may or may not take place. Coupled with the discussion raised in
viii
recommendation 4, there is a reasonable probability that during a SAR mission for an Ovatek life
raft that the configuration could well be a full life raft drifting without a sea anchor.
ix
TABLE OF CONTENTS
ACKNOWLEDGEMENTS ..................................................................................................................................... III
EXECUTIVE SUMMARY ...................................................................................................................................... IV
TABLE OF CONTENTS ...........................................................................................................................................X
LIST OF FIGURES.................................................................................................................................................XII
LIST OF TABLES................................................................................................................................................. XIV
LIST OF ACRONYMS ...........................................................................................................................................XV
1.0
INTRODUCTION ...........................................................................................................................................1
1.1
BACKGROUND ...........................................................................................................................................1
1.2
PROJECT OBJECTIVES ..............................................................................................................................3
1.2.1
PHASE I OVATEK LEEWAY.................................................................................................................4
1.2.2
PHASE II OVATEK LEEWAY ...............................................................................................................4
1.2.3
USCG OBJECTIVES .............................................................................................................................5
1.3
RELATED DOCUMENTS ...................................................................................................................................5
2.0
PROJECT METHODOLOGY.......................................................................................................................7
2.1
PROJECT TASKS ..............................................................................................................................................7
2.2
SAR OBJECTS.................................................................................................................................................9
2.2.1
Instrumentation....................................................................................................................................11
2.2.2
SAR Object Configurations..................................................................................................................16
2.2.3
Data Collection Parameters ................................................................................................................19
2.3
FIELD TRIALS LOCATION AND TIME FRAME....................................................................................20
2.4
COAST GUARD SUPPORT VESSELS .....................................................................................................21
2.5
TYPICAL DRIFT RUN SCENARIO....................................................................................................................24
2.5.1
Deployment and Recovery Planning....................................................................................................24
2.5.2
Transit and Deployment.......................................................................................................................25
2.5.3
Tracking...............................................................................................................................................26
2.5.4
Recovery ..............................................................................................................................................26
2.6
LEEWAY DETERMINATION............................................................................................................................27
3.0
DATA REDUCTION AND ANALYSIS METHODOLOGY ....................................................................28
3.1
DATA REDUCTION ........................................................................................................................................28
3.2
SUMMARY OF THE OVATEK LIFE RAFT LEEWAY DATASET ..........................................................................31
3.3
ANALYSIS METHODOLOGY ...........................................................................................................................34
3.3.1
Definition of Leeway and Measurement Reference Levels ..................................................................34
3.3.2
Leeway Vectors ....................................................................................................................................34
3.3.3
Regression Models...............................................................................................................................34
4.0
RESULTS AND DISCUSSION ....................................................................................................................39
4.1
LIGHTLY-LOADED OVATEK LIFE RAFTS WITHOUT DROGUE ........................................................................39
4.1.1
Leeway Speed.......................................................................................................................................39
4.1.2
Leeway Angle Divergence ...................................................................................................................44
4.1.3
Progressive Leeway Displacement Plots .............................................................................................44
4.1.4
Downwind and Crosswind Leeway Components .................................................................................51
4.2
FULLY-LOADED OVATEK LIFE RAFTS WITH DROGUE ..................................................................................60
x
4.2.1
4.2.2
4.2.3
Leeway Speed.......................................................................................................................................60
Leeway Angle Divergence ...................................................................................................................64
Downwind and Crosswind Leeway Components .................................................................................67
5.0
CONCLUSIONS ............................................................................................................................................75
6.0
RECOMENDATIONS ..................................................................................................................................77
7.0
REFERENCES ..............................................................................................................................................79
xi
LIST OF FIGURES
FIGURE 1-1 7-PERSON OVATEK LIFE RAFT ....................................................................................................................2
FIGURE 1-2 OVATEK LIFE RAFTS IN ST. JOHN'S..............................................................................................................2
FIGURE 2-1 OVATEK 4-PERSON LIFE RAFT....................................................................................................................9
FIGURE 2-2 OVATEK 7-PERSON LIFE RAFT....................................................................................................................9
FIGURE 2-3 SUBMARINE EMERGENCY INDICATING RADIO BEACON (SEPIRB)............................................................10
FIGURE 2-4 SUBMARINE ESCAPE AND IMMERSION EQUIPMENT (SEIE) LIFE RAFT ......................................................10
FIGURE 2-5 SIMULATED COCAINE BALE ......................................................................................................................10
FIGURE 2-6 METOCEAN SLDMB.................................................................................................................................11
FIGURE 2-7 SEIMAC SELF LOCATING DATA MARKER BUOY ........................................................................................11
FIGURE 2-8 OVATEK DATA LOGGER SETUP .................................................................................................................12
FIGURE 2-9 INSIDE OF OVATEK LIFE RAFT ...................................................................................................................13
FIGURE 2-10 INSTRUMENTED AND OUTFITTED 4-PERSON OVATEK LIFE RAFT ............................................................14
FIGURE 2-11 INSTRUMENTED 4-PERSON LIFE RAFT AT SEA .........................................................................................14
FIGURE 2-12 INSTRUMENTED AND OUTFITTED 7-PERSON OVATEK LIFE RAFT ............................................................15
FIGURE 2-13 INSTRUMENTED 7-PERSON LIFE RAFT AT SEA .........................................................................................15
FIGURE 2-14 DATAWELL MKII DIRECTIONAL WAVEBUOY .........................................................................................16
FIGURE 2-15 OVATEK 4-PERSON LIFE RAFT DEPLOYED WITH DROGUE ......................................................................17
FIGURE 2-16 OVATEK 4-PERSON LIFE RAFT DEPLOYED WITHOUT DROGUE ...............................................................17
FIGURE 2-17 OVATEK 7-PERSON LIFE RAFT DEPLOYED WITH DROGUE ......................................................................18
FIGURE 2-18 OVATEK 7-PERSON LIFE RAFT DEPLOYED WITHOUT DROGUE ...............................................................18
FIGURE 2-19 PHASE I OPERATIONS AREA ....................................................................................................................20
FIGURE 2-20 PHASE II OPERATIONS AREA ...................................................................................................................21
FIGURE 2-21 CCGS “HARP” .......................................................................................................................................22
FIGURE 2-22 PHASE I OVATEK RECOVERY ...................................................................................................................22
FIGURE 2-23 CCGS "ANN HARVEY"............................................................................................................................23
FIGURE 2-24 PHASE II OVATEK DEPLOYMENT .............................................................................................................23
FIGURE 2-25 INTEROCEAN S4 CURRENT METER IN TOW FRAME .................................................................................27
FIGURE 3-1 PHASE I DRIFT TRACKS .............................................................................................................................32
FIGURE 3-2 PHASE II DRIFT TRACKS ............................................................................................................................33
FIGURE 3-3 RELATIONSHIPS BETWEEN LEEWAY SPEED AND ANGLE AND THE DOWNWIND AND CROSSWIND LEEWAY
COMPONENTS .......................................................................................................................................................36
FIGURE 4-1 LEEWAY SPEED AGAINST 10 M WIND SPEED - OVATEK 4-PERSON LIFE RAFT, LIGHTLY-LOADED WITHOUT
DROGUE ................................................................................................................................................................40
FIGURE 4-2 LEEWAY SPEED AGAINST 10 M WIND SPEED - OVATEK 7-PERSON LIFE RAFT, LIGHTLY-LOADED WITHOUT
DROGUE ................................................................................................................................................................41
FIGURE 4-3 LEEWAY SPEED AGAINST 10 M WIND SPEED - OVATEK 4- AND 7-PERSON LIFE RAFTS, LIGHTLY-LOADED
WITHOUT DROGUE ................................................................................................................................................43
FIGURE 4-4 PROGRESSIVE LEEWAY DISPLACEMENTS: OVATEK 4- AND 7-PERSON RIGID LIFE RAFTS,.........................45
FIGURE 4-5 PROGRESSIVE LEEWAY DISPLACEMENTS – ENLARGED SCALE ...................................................................46
FIGURE 4-6 SAMPLE TIME-SERIES PLOT DURING LEEWAY DRIFT RUN 078 .................................................................47
FIGURE 4-7 TIME-SERIES PLOT AT THE START OF DRIFT RUN 074 ...............................................................................48
FIGURE 4-8 LEEWAY ANGLE AND WIND SPEED, OVATEK 4- PERSON LIFE RAFT, LIGHTLY-LOADED WITHOUT DROGUE
.............................................................................................................................................................................50
FIGURE 4-9 LEEWAY ANGLE AND WIND SPEED, OVATEK 7-PERSON LIFE RAFTS, LIGHTLY-LOADED WITHOUT DROGUE
.............................................................................................................................................................................51
FIGURE 4-10 DOWNWIND LEEWAY - OVATEK 4-PERSON RIGID LIFE RAFT, LIGHTLY-LOADED WITHOUT DROGUE .....53
FIGURE 4-11 CROSSWIND LEEWAY - OVATEK 4-PERSON LIFE RAFT, LIGHTLY-LOADED WITHOUT DROGUE ...............54
FIGURE 4-12 DOWNWIND LEEWAY - OVATEK 7-PERSON RIGID LIFE RAFT, LIGHTLY-LOADED WITHOUT DROGUE .....55
FIGURE 4-13 CROSSWIND LEEWAY - OVATEK 7-PERSON RIGID LIFE RAFT, LIGHTLY-LOADED WITHOUT DROGUE .....56
FIGURE 4-14 DOWNWIND LEEWAY - OVATEK 4- AND 7-PERSON RIGID LIFE RAFTS, LIGHTLY-LOADED WITHOUT
DROGUE ...............................................................................................................................................................57
xii
FIGURE 4-15 CROSSWIND LEEWAY- OVATEK 4- AND 7-PERSON RIGID LIFE RAFT, LIGHTLY-LOADED WITHOUT
DROGUE ...............................................................................................................................................................58
FIGURE 4-16 LEEWAY SPEED AGAINST 10 M WIND SPEED – OVATEK 4-PERSON RIGID LIFE RAFT, FULLY-LOADED
WITH DROGUE ......................................................................................................................................................61
FIGURE 4-17 LEEWAY SPEED AGAINST 10 M WIND SPEED – OVATEK 7-PERSON RIGID LIFE RAFT, FULLY-LOADED
WITH DROGUE ......................................................................................................................................................62
FIGURE 4-18 LEEWAY SPEED AGAINST 10 M WIND SPEED – OVATEK 4- AND 7-PERSON RIGID LIFE RAFT, FULLYLOADED WITH DROGUE ........................................................................................................................................63
FIGURE 4-19 PROGRESSIVE LEEWAY DISPLACEMENTS: OVATEK 4-AND 7-PERSON RIGID LIFE RAFTS, FULLY-LOADED
WITH DROGUE ......................................................................................................................................................65
FIGURE 4-20 LEEWAY ANGLE SCATTER PLOT - OVATEK 4- AND 7-PERSON LIFE RAFTS, FULLY-LOADED WITH DROGUE
.............................................................................................................................................................................66
FIGURE 4-21 DOWNWIND LEEWAY - OVATEK 4-PERSON RIGID LIFE RAFT, FULLY-LOADED WITH DROGUE................68
FIGURE 4-22 CROSSWIND LEEWAY - OVATEK 4-PERSON RIGID LIFE RAFT, FULLY-LOADED WITH DROGUE ...............69
FIGURE 4-23 DOWNWIND LEEWAY - OVATEK 7-PERSON RIGID LIFE RAFT, FULLY-LOADED WITH DROGUE................70
FIGURE 4-24 CROSSWIND LEEWAY - OVATEK 7-PERSON RIGID LIFE RAFT, FULLY-LOADED WITH DROGUE ...............71
FIGURE 4-25 DOWNWIND LEEWAY - OVATEK 4- AND 7-PERSON RIGID LIFE RAFTS, FULLY-LOADED WITH DROGUE ..72
FIGURE 4-26 CROSSWIND LEEWAY - OVATEK 4- AND 7-PERSON RIGID LIFE RAFTS, FULLY-LOADED WITH DROGUE ..73
xiii
LIST OF TABLES
TABLE 1-1 PROJECT RELATED DOCUMENTS...................................................................................................................6
TABLE 3-1 DRIFT RUN DATA COLLECTION SUMMARY.................................................................................................31
TABLE 3-2 OVATEK LIFE RAFT CONFIGURATION DATA SUMMARY .............................................................................34
TABLE 4-1 LINEAR REGRESSION MODELS OF LEEWAY SPEED ON 10 M WIND SPEED FOR OVATEK 4- AND 7-PERSON
RIGID LIFE RAFTS, LIGHTLY-LOADED WITHOUT DROGUE ....................................................................................42
TABLE 4-2 LEEWAY ANGLE STATISTICS - OVATEK 4- AND 7-PERSON RIGID LIFE RAFTS LIGHTLY-LOADED WITHOUT
DROGUE ...............................................................................................................................................................49
TABLE 4-3 DOWNWIND AND CROSSWIND REGRESSION MODELS FOR LIGHTLY-LOADED OVATEK 4- AND 7-PERSON
LIFE RAFTS WITHOUT DROGUE ............................................................................................................................59
TABLE 4-4 LINEAR REGRESSION MODELS OF LEEWAY SPEED ON 10 M WIND SPEED FOR OVATEK 4-AND 7-PERSON
RIGID LIFE RAFTS, FULLY-LOADED WITH DROGUE ..............................................................................................60
TABLE 4-5 LEEWAY ANGLE STATISTICS - OVATEK 4- AND 7-PERSON LIFE RAFTS, FULLY-LOADED WITH DROGUE ...64
TABLE 4-6 DOWNWIND AND CROSSWIND REGRESSION MODELS - OVATEK 4- AND 7-PERSON LIFE RAFTS, FULLYLOADED WITH DROGUE ........................................................................................................................................74
xiv
LIST OF ACRONYMS
APLwaves
ARGOS
CANSARP
CCG
CCGS
DFO
DGPS
EPIRB
GPS
NIF
NSS
PTT
S4
SAIC
SAR
SEIE
SEPIRB
SLDMB
SOLAS
TDC
USCG
John Hopkins Applied Physics Laboratory Waves Analysis Software
A Satellite-based Location and Data Collection System
Canadian Search and Rescue Planning
Canadian Coast Guard
Canadian Coast Guard Ship
Department of Fisheries and Oceans
Differential Global Positioning System
Emergency Position Indicating Radio Beacon
Global Positioning System
New Initiatives Fund
National SAR Secretariat
Platform Transmitter Terminal
InterOcean S4 current meter
Science Applications International Corporation
Search and Rescue
Submarine Escape and Immersion Equipment
Submarine Emergency Position Indicating Radio Beacon
Self Locating Data Marker Buoy
Safety of Life at Sea
Transportation Development Centre
United States Coast Guard
xv
1.0
INTRODUCTION
A two-phase project was conducted by OCEANS Ltd. during fiscal years 2004/2005 and
2005/2006 to investigate the Leeway and Drift of Ovatek Life Rafts on behalf of the Canadian
Coast Guard (CCG). Primary funding for the project was provided by the National SAR
Secretariat (NSS). In-kind support was provided by OCEANS Ltd., CCG, and the United States
Coast Guard (USCG). Phase I of the project was completed during the 04/05 fiscal year and
Phase II completed during the 05/06 fiscal year. This document constitutes the OCEANS Ltd.
Final Report for the project (NIF ID 2004033, DFO 2/04). Included in the report will be the
following:
1.1
background information on the project
overall project objectives
project methodology
project objectives
data reduction and analysis
preliminary results and discussion
recommendations for future projects
BACKGROUND
In the late 1980’s to mid 1990’s OCEANS Ltd. personnel, with support from CCG,
Transportation Development Centre (TDC), and USCG conducted a number of leeway
experiments for common SAR objects in environmental conditions typically encountered on the
east coast of Canada. The National SAR Manual (DFO, 1998) defines “leeway” as the
“movement of the search object through water caused by the action of wind on the exposed
surfaces of the object”. The objects tested in these earlier studies included:
-
4, 6, and 20-person inflatable life rafts
small open plank boats
22-person SOLAS approved fibreglass life capsule
46-person L1011 passenger slide / life raft
an air deployable Sea Rescue Kit consisting of three 6-person life rafts and two survival
packs
The results of these studies have been incorporated in the National SAR Manual and into the
Canadian Search and Rescue Planning (CANSARP) tool. CANSARP is a computer tool used to
1
plan search operations. It uses the target’s leeway characteristics, visual characteristics, and
environmental factors such as ocean currents and winds to determine probable target drift
trajectories.
In recent years Ovatek Inc., based in New Brunswick, has developed and marketed a new type of
SAR object, the 4-person and 7-person Ovatek rigid life raft.
Figure 1-1 7-Person Ovatek Life Raft
Ovatek life rafts have been approved by SOLAS, CCG, and the USCG. In recent years they have
become a popular alternative to the inflatable life raft on board fishing vessels in Atlantic Canada
and the west coast of North America.
Figure 1-2 Ovatek Life Rafts in St. John's
An incident involving an Ovatek life raft highlighted the need for leeway data for these SAR
targets. In the spring of 2003 a SAR operation (Incident L2003-0034 Quebec Region) was
conducted for a 7-person Ovatek life raft in the Gulf of St. Lawrence. The life raft belonged to
2
the MV “Caboteur” that sank on April 4, 2003 at 1215 EST. Fortunately in this case a vessel was
standing close by when the ship sank and the 6-man crew was recovered from the life raft within
an hour with no injuries. The life raft and the Caboteur’s EPIRB were recovered 2 days later on
April 6, 2003. However, the incident report noted that the position of the search objects was very
different than the positions calculated by CANSARP. Further, it stated that upon examination of
the incident it is evident that the Ovatek life raft did not have the same “rhythm of drift” as a
conventional life raft. In an effort to improve the accuracy of CANSARP predictions, a leeway
study was proposed and conducted on 4-person and 7-person Ovatek life rafts. The field trials
and analysis followed a general approach used successfully by OCEANS Ltd. in previous leeway
work. The details of this work are discussed in the remainder of this report.
As well, at the outset of this project the USCG was invited to participate. Dating back to the late
1980s OCEANS Ltd. personnel, on behalf of the Canadian Coast Guard, have successfully
carried out several leeway and drift experiments off Newfoundland in partnership with the
USCG. During the Phase I field trials the USCG supported this project through the supply of
various instrumentation and equipment. During the Phase II field trials the USCG and their
contractor, Science Applications International Corp. (SAIC) took part in field operations and
collected leeway data on three targets of interest to the USCG. The targets included Submarine
Escape and Immersion Equipment (SEIE) life rafts, Submarine Emergency Position Indicating
Radio Beacons (SEPIRB) and simulated cocaine bales. Further information on USCG targets,
objectives and participation is provided throughout this document.
1.2
PROJECT OBJECTIVES
The primary Ovatek leeway project objective was to:
“determine a functional relationship between wind velocity and leeway speed and
angle for the 4-person and 7-person Ovatek rigid life rafts in operationally
limiting configurations for inclusion in the National SAR Manual (DFO, 1998)
and CANSARP.”
A secondary project objective was to:
“to investigate improved analysis methodologies for obtaining SAR object leeway
angles off the downwind direction with the goal of increasing the precision of
3
leeway angle divergence and, ultimately, reducing search area, search time, and
SAR resource requirements.”
Interim objectives were established for each phase of the project to satisfy the above goals. As
well, the USCG conducted a field program in cooperation with the Phase II Ovatek field study.
The objectives of their research as well as a discussion of the Phase I and II interim objectives
follows below.
1.2.1
PHASE I OVATEK LEEWAY
Primary Objectives
1.
Collect and analyze preliminary field data for determining the leeway for the 4- and 7person Ovatek life rafts in wind speeds up to 25 knots. Life rafts were to be configured
as follows:
-
2.
light loading (1 person on board) without sea anchor deployed
maximum loading (4- or 7-person on board) with sea anchor deployed
In preparation for the Phase II trials planned for the Fall of 2005 the work in Phase I was
to serve as a test of equipment, deployment/recovery procedures, scientific
instrumentation, and communications.
Secondary Objectives
1.
Collect field data for determining the leeway for the research sailboat “Tigger”.
1.2.2
PHASE II OVATEK LEEWAY
Primary Objectives
3. Collect and analyze field data for determining the leeway for the 4- and 7-person Ovatek
life rafts in wind speeds up to 50 knots. Life rafts were to be configured as follows:
-
light loading (1 person on board) without sea anchor deployed
maximum loading (4- or 7-person on board) with sea anchor deployed
4
4. Determine a functional relationship between wind velocity and leeway speed and angle
for the 4-person and 7-person Ovatek rigid life rafts in operationally limiting
configurations for inclusion in the National SAR Manual (DFO, 1998) and CANSARP.
5. Investigate improved analysis methodologies for obtaining SAR leeway angles off the
downwind direction with the goal of increasing the precision of leeway angle divergence
and, ultimately, reducing the search area, search time, and SAR resource requirements.
Secondary Objectives
1. Carry out a drift characteristics comparison of the MetOcean SLDMB versus the Seimac
SLDMB.
1.2.3
USCG OBJECTIVES
1. Collect field data for determining the leeway of a SEPIRB.
2. Collect field data for determining the leeway of a SEIE life raft configured with and
without a sea anchor.
3. Collect field data for determining the leeway of simulated cocaine bales.
Leeway data was acquired by deploying SLDMBs in the vicinity of the above leeway targets.
Environmental data was collected using an Aanderra Coastal Monitoring Buoy and wave data
from a Datawell Directional Waverider buoy. In the case of the SEIE life rafts, a single life raft
was outfitted with an RDI Sentinel Acoustic Doppler Current Profiler current meter to collect
leeway speed directly.
1.3
Related Documents
The following documents were also prepared as part of this project and will be submitted on CD
with the final of this report.
5
Table 1-1 Project Related Documents
Document Number
Document Title
11340
11340_PWP_P1
11340_FP_P1
11340_FR_P1
11340_SR_P1
11340_PWP_P2
11340_FP_P2
11340_FR_P2
Project Proposal
Phase I Project Work Plan
Phase I Field Plan
Phase I Field Report
Phase I Summary Report
Phase II Project Work Plan
Phase II Field Plan
Phase II Field Report
6
2.0
PROJECT METHODOLOGY
The following sections provide details on the leeway targets, equipment and methods used to
perform the Ovatek field experiment. These sections also give a brief overview of the USCG
targets and their involvement in the field trials.
2.1
Project Tasks
This section provides an overview of the Phase I and II project tasks. Much of the preparatory
work performed during Phase I and II was carried out simultaneously in order to meet project
schedules. The following is a list of the tasks and subtasks performed in each phase.
1. Phase I activities
1.1. Preparation and mobilization for phase I field trials
1.1.1. Preparation of the phase I work plan
1.1.2. Research, source and procure project instrumentation and equipment
1.1.3. Prepare, test and mobilize project instrumentation and equipment
1.1.4. Prepare a field trial plan
1.2. Conduct phase I field trials
1.2.1. Identification of support vessel and field trial time frame
1.2.2. Logistics and personnel
1.2.3. Meeting with support vessel crew
1.2.4. Transport of project instrumentation and equipment to coast guard base
1.2.5. Mobilization of project instrumentation and equipment on support vessel
1.2.6. Weather forecast support
1.2.7. Target tracking and communications
1.2.8. Directional wave data collection
1.2.9. Daily drift run scenario
1.2.10. De-mobilization of project instrumentation and equipment from support vessel
1.3. Phase I data analysis and interim report preparation
1.3.1. Preparation of phase I field report
1.3.2. Field data consolidation and preliminary quality control
1.3.3. Submission and presentation of field trial report
1.3.4. Data reduction and analysis of Phase I leeway data
1.3.5. Preparation of Phase I summary report
1.3.6. Presentation of Phase I summary report
7
1.3.7. Finalization of Phase I report
1.4. Phase I NIF sponsor project management
1.4.1. NIF sponsor project management activities
2. Phase II activities
2.1. Preparation and mobilization for Phase II field trials
2.1.1. Review recommendations of Phase I final report
2.1.2. Evaluate equipment and instrumentation performance from Phase I
2.1.3. Preparation of the phase II work plan
2.1.4. Procure required project instrumentation and equipment
2.1.5. Prepare, test and mobilize project instrumentation and equipment
2.1.6. Prepare a field trial plan
2.2. Conduct Phase II field trials
2.2.1. Identification of field trial operations area and time frame
2.2.2. Identification of support vessel
2.2.3. Logistics and personnel
2.2.4. Meeting with support vessel crew
2.2.5. Transport of project instrumentation and equipment to coast guard base
2.2.6. Mobilization of project instrumentation and equipment on support vessel
2.2.7. Weather forecast support
2.2.8. Target tracking and communications
2.2.9. Directional wave data collection
2.2.10. Daily drift run scenario
2.2.11. De-mobilization of project instrumentation and equipment from support vessel
2.3. Phase II data analysis and final report preparation
2.3.1. Preparation of Phase II field report
2.3.2. Field data consolidation and preliminary quality control
2.3.3. Submission and presentation of field trial report
2.3.4. Data reduction and analysis of phase ii leeway data
2.3.5. Preparation of final project draft report
2.3.6. Presentation of final project draft report
2.3.7. Finalization of final project report
2.3.8. French Translation and submission of final project report
2.4. Phase II NIF sponsor project management
2.4.1. NIF sponsor project management activities
2.4.2. Preparation and implementation of project communications plan
8
2.2
SAR Objects
The primary leeway objects for project were the 4- and 7-person Ovatek Life Rafts. The life
rafts are seen in Figure 2-1 and Figure 2-2.
Figure 2-1 Ovatek 4-Person Life Raft
The general specifications of the 4-person life raft are:
`
Length
Width
Height
Weight
Full Load
Ballast
2.1 m
1.3 m
1.1 m
115kg/250 lb
430kg/950 lb
External
Figure 2-2 Ovatek 7-Person Life Raft
The general specifications of the 7-person life raft are:
9
Length
Width
Height
Weight
Full Load
Ballast
2.8 m
1.3 m
1.4 m
182kg/400 lb
740kg/1600 lb
100 litre internal
The USCG leeway targets include a SEPIRB, SEIE life raft and simulated cocaine bales. The
targets are shown in Figure 2-3 through Figure 2-5 respectively.
Figure 2-3 Submarine Emergency Indicating Radio Beacon (SEPIRB)
Figure 2-4 Submarine Escape and Immersion Equipment (SEIE) Life Raft
Figure 2-5 Simulated Cocaine Bale
Figure 2-6 and Figure 2-7 respectively show the MetOcean and Seimac SLDMBs.
10
Figure 2-6 MetOcean SLDMB
Figure 2-7 Seimac Self Locating Data Marker Buoy
2.2.1
Instrumentation
During the 2004 and 2005 field programs, data were collected from a set of sensors attached to
each Ovatek life raft. This equipment logged meteorological parameters, life raft position, and
heading. The S4 current meter frame was tethered to the life raft via a 20m line. As well, an
ORBCOMM satellite communications system was installed to transmit the life raft’s position
and various status indicators back to shore at regular intervals. As a backup, an ARGOS PTT
was installed inside the life raft to transmit position for recovery purposes. The data logger and
sensors were powered with two 12V sealed lead acid batteries which provided enough power for
11
approximately 7 days of operation. The following is a complete listing of equipment installed
onboard the Ovatek life rafts:
-
R.M. Young anemometer system
Campbell Scientific 107B air/water temperature sensors
Honeywell HMR3300 3-axis compass system (Phase I)
KVH AutoComp 1000S tilt-tompensated flux gate compass (Phase II)
Campbell Scientific CR10X data logger
Two 12V 26AHr sealed lead acid batteries
InterOcean S4 current meter
Garmin 16 GPS receiver
Garmin GBR21 DGPS beacon receiver / CSI Wireless SBA-1 DGPS beacon receiver
Orbcomm satellite communications system
c/w Stellar Satellite ST2500 transceiver with service from ROM Communications
Seimac SmartCat ARGOS PTT
Novatech VHF beacon
Mobri S-2 radar reflector
The data logger, satellite communications transceiver, and batteries were installed inside a
watertight Pelican™ case. The case and electronics are shown in Figure 2-8.
Figure 2-8 Ovatek Data Logger Setup
The case was secured inside the life rafts and the sensors were connected via waterproof
connectors. Figure 2-9 shows the complete system mounted inside of a life raft.
12
Compass
Sandbag
Plywood Floor &
Bracing
ARGOS PTT
Pelican™ Case
Figure 2-9 Inside of Ovatek Life Raft
Figure 2-10 through Figure 2-13 illustrate the external configuration for the 4-person and 7person life rafts respectively.
13
Figure 2-10 Instrumented and Outfitted 4-Person Ovatek Life Raft
Figure 2-11 Instrumented 4-Person Life Raft at Sea
14
Anemometer
Guywire
3-Point
Lifting
Strap
Air Temperature
Sensor
Satellite
Communications
Antenna
Mast
GPS
Floor & Floor
Supports
Water
Temperature
Sensor
Compass
Datalogger &
Communications
Package
Belly Strap
Waterline
Figure 2-12 Instrumented and Outfitted 7-Person Ovatek Life Raft
Figure 2-13 Instrumented 7-Person Life Raft at Sea
15
A Datawell Directional waverider buoy, shown in Figure 2-14, was deployed in the operations
area. This buoy was primarily used as an operational tool during field trials to determine
appropriate deployment schedules. The Datawell buoy transmits data to a receiving station via a
high frequency radio
Figure 2-14 Datawell MKII Directional Wavebuoy
link. During Phase I, the receiving station was set up in a Canadian Coast Guard building at Cape
Spear. For Phase II, the receiving station was set up at OCEANS Ltd.’s office in St. John’s.
2.2.2
SAR Object Configurations
Both life rafts were deployed in two configurations during the trials. The configurations
included 1-person loading without a drogue and full loading with a drogue deployed. The
drogue, SOLAS approved and manufactured by Ovatek, was a nylon cone with swivel and nylon
rode. The drogue, with a rode of 30.5 m, has a cone 0.64 m in length with the wide opening
being 0.6 m and the narrow opening being .08 m.
Approximately 22 kg sand bags were used for ballast. The weight of one person was considered
to be 79.5 kg. The life rafts were outfitted with plywood floors and aluminum support bracing to
accommodate the mounting of equipment and ballast inside the life rafts. A 3-point lifting bridle
was used deploy and recover the life raft. The bridle was made from 2-ply x 2” nylon strapping
and had a safe working load of 3000 lbs @ 30º from vertical.
In the lightly-loaded configuration a belly strap, swivel and stiff rope arrangement was used to
attach the S4 tether to the life raft. This ensured the life raft’s orientation was not influenced by
the S4 current meter assembly.
16
Figure 2-15 and Figure 2-16 show the 4-person life raft in its deployed configuration with and
without a drogue deployed respectively. Figure 2-17 and Figure 2-18 show the 7-person life raft
in its deployed configuration with and without a drogue deployed respectively.
Figure 2-15 Ovatek 4-Person Life Raft Deployed With Drogue
Figure 2-16 Ovatek 4-Person Life Raft Deployed Without Drogue
17
Figure 2-17 Ovatek 7-Person Life Raft Deployed With Drogue
Figure 2-18 Ovatek 7-Person Life Raft Deployed Without Drogue
18
2.2.3
Data Collection Parameters
Positional information on the SAR objects was obtained through GPS, ARGOS PTT's and VHF
beacons. GPS positions were logged every five minutes using the CR10X data logger and
emailed to OCEANS Ltd. hourly via the ORBCOMM system. The GPS data was subsequently
used to derive true wind at the SAR objects and to obtain total drift displacement. ARGOS
positions were updated every 2 to 3 hours and were obtained on a routine basis from the ARGOS
website via the USCG International Ice Patrol. The VHF beacons provided SAR object direction
when the vessel was within VHF range (approximately 10 nm) of the SAR object.
SAR object headings were determined using a 3-axis compass system. In Phase I a Honeywell
HMR3300 tilt-compensated compass was used to determine heading. These units also provided
pitch and roll information. Due to communication problems, they were replaced with KVH
Autocomp 1000s compasses in Phase II. The KVH units are internally gimbaled and did not
provide pitch and roll information. Wind direction was computed from a 10-minute unit vector
average using a sampling interval of one second. The standard deviation of wind direction was
computed following the algorithm described by Yamartimo (1984). Average wind speed
recorded was simply the scalar mean apparent wind speed over the sampling period. Ten-minute
maximum 1-second apparent wind speed was also recorded.
For all drift runs the S4 current meters were programmed to provide 10-minute vector averages
of the half-second velocity component samples. Data collection times for the instrumentation
packages on board the SAR objects were synchronized with the S4 data collection program.
Air and sea temperature was recorded every 10 minutes. These data were used in the adjustment
of the true wind to the 10 m reference height.
The following wave data was recorded by the Datawell waverider system hourly:
wave direction
significant wave height
maximum wave height
mean zero crossing period
peak period
spectral data
statistics data
19
2.3
raw data
sea temperature
FIELD TRIALS LOCATION AND TIME FRAME
The Phase I field trials were conducted off Cape Spear, Newfoundland. The general operations
area was approximately 20 nm X 20 nm (400 square nautical miles). The centre of the operations
area was approximately 15 nautical miles east of Cape Spear. A Datawell directional waverider
buoy was deployed within the operations area. The Phase I field trials were conducted during the
period September 1 –17, 2004. The field trial location is shown in Figure 2-19. The deployment
position for the rafts was planned so that the Ovatek life rafts would likely stay within the
operations area during their drift run.
47°40'N
52°30'W
40'
35'
47°40'N
52°01'W
Phase I General Operating Area
St. John′s
Cape Spear
o
47 N
30.00'
Wavebuoy
47°29.8'N
52°20.7'W
25'
20'
47°20'N
52°30'W
40'
47°20'N
52°01'W
30'
20'
10'
o
52 W
Figure 2-19 Phase I Operations Area
For the second phase of the leeway project it was intended that the Ovatek life rafts would be
deployed for 3-4 day periods. Therefore, the general operations area was enlarged to
approximately 90 nm X 90 nm (8100 square nautical miles). The field trial area is shown in
Figure 2-20. As with Phase I, the deployment position for the life rafts was planned so that the
20
Ovatek life rafts would likely stay within the operations area. The smaller USCG targets
(SEPIRBs, SEIE life rafts, cocaine bales and SLDMBs) were deployed for 1-2 day periods
before recovery was attempted. Essentially, these smaller targets were deployed upwind of the
moored wave and meteorological buoy with the intent that their drift tracks would pass in close
proximity to the moored buoys. Therefore, the directional wave data and meteorological data
reflected the conditions being experienced by the leeway targets as closely as possible.
30'
o
48 N
48°00'N
52°30'W
48°00'N
50°18'W
Phase II General Operating Area
Metbuoy
47°37.5'N
52°16.0'W
Wavebuoy
47°34.4'N
52°13.8'W
30'
o
47 N
30'
o
46 N o
53 W
46°30'N
52°30'W
30'
46°30'N
50°18'W
o
30'
52 W
o
51 W
30'
o
50 W
Figure 2-20 Phase II Operations Area
2.4
COAST GUARD SUPPORT VESSELS
The primary support vessel for the Phase I Field Trials was the CCGS “Harp”. The CCGS
"Harp", shown in Figure 2-21 and Figure 2-22, is a small multi-task ice strengthened cutter. The
21
overall length is 24.5 m with a beam of 7.6 m and a draft of 2.5 m. Deck space is minimal but
was adequate for the stowage and management of project equipment including the 4- and 7person Ovatek life rafts. The after deck is equipped with a PM Autogru crane and an inflatable
runabout. The crane, with a safe working load of 1400 kg at 7.5 m reach was adequate for
handling both life rafts within trial operational limits for deployment and recovery of the Ovatek
life rafts. After some experience was gained, the operating limits were deemed to be less than
1.8 m significant wave height. The low freeboard facilitated the handling of SAR objects and
equipment over the side.
Figure 2-21 CCGS “HARP”
Figure 2-22 Phase I Ovatek Recovery
22
The primary support vessel for the Phase II Field Trials was the CCGS “Ann Harvey”. The
CCGS "Ann Harvey", shown in Figure 2-23 and Figure 2-24, is a light icebreaker/major navaids
tender. The overall length is 83 m with a beam of 16.2 m and a draft of 6.2 m. Space on the
forward deck was more than adequate for the stowage and management of project equipment
including the 4- and 7-person Ovatek life rafts. The main hold was also used as an area to
perform life raft maintenance and was used for equipment stowage. The forward crane’s reach
and capacity easily accommodated the deployment and recovery of the Ovatek life rafts and the
USCG targets. The higher freeboard made recovery operations slightly more difficult than the
previous year. However, the vessel’s stability was an asset. After some experience was gained,
the operating limits were deemed to be on the order of 3 m significant wave height.
Figure 2-23 CCGS "Ann Harvey"
Figure 2-24 Phase II Ovatek Deployment
23
Equipment was required onboard both support vessels for tracking the SAR objects at sea. Both
the CCGS “Harp” and “Ann Harvey” had VHF direction finders previously installed. As well, a
GONIO 400 ARGOS direction finder unit was temporarily installed on both vessels to assist
with target tracking. Also, a connection was provided to the “Ann Harvey’s” GlobalStar Satellite
system to allow for collection of position data from the internet.
2.5
Typical Drift Run Scenario
As stated in the project objectives, the Phase I field trials were used as an opportunity to collect data
in light wind conditions. This also served as a test of equipment, deployment/recovery procedures,
instrumentation, and communications systems in preparation for the Phase II trials. For Phase II the
goal was to obtain data for wind speeds up to 50 knots. A typical drift run was completed in 4
stages: deployment location planning, transit and deployment, target tracking, and recovery. The
details of these stages are discussed in the following sections.
2.5.1
Deployment and Recovery Planning
Prior to leaving port, actual and predicted weather and sea conditions were assessed and discussed
with the Captain. This was normally done in the evening prior to sailing and again in the morning
before a sailing time was finalized. To assist in the “go or no-go” decision-making, certain tools
were utilized. These decision-making tools included the following:
1.
A 5-day marine site-specific forecast provided to the project from the OCEANS Ltd.
Weather Office. These forecasts were issued daily.
2.
An Oceanogram for the operations area provided by OCEANS Ltd. that was accessed at
the OCEANS Ltd. website. The Oceanogram provided a 7-day forecast of winds and
waves for selected points within the operations area.
3.
Wave parameters from the directional waverider buoy deployed in the operations area
were checked.
For the Phase I trials drifts were expected to last between 12 and 24 hours. This limited the total
drift distance in case of equipment failure. Generally the life rafts were deployed in the late
morning and retrieved in the early afternoon of the following day. During Phase II the Ovatek
24
life rafts were deployed in reasonably good weather ahead of an impending weather system. The
life rafts remained at sea while the weather system passed through the region and tracked from
shore. They were then recovered in good weather conditions after the system had passed through
the area. It was hoped to limit the duration of a drift run to less than seven (7) days. The life rafts
were always deployed and recovered within the operating limits of the vessel.
Once it was decided that conditions looked suitable for the deployment of SAR objects, based on
the above criteria, a deployment plan was finalized. The deployment plan usually included deciding
a deployment location and setting a sailing time. Every effort was made to deploy the life rafts in
a location that would keep them within the operating area and in the general area of the
directional waverider buoy, particularly in Phase I. Deployment locations were generally upwind
of the wave buoy. Therefore the wave data being collected by the wave buoy was relevant to what
was being experienced by the life rafts.
2.5.2
Transit and Deployment
OCEANS Ltd. personnel prepared the Ovatek life rafts for deployment. Usually the life rafts were
prepared for deployment the day before sailing with final preparations being made on the departure
day prior to leaving port for the deployment location. The actual deployment of the life rafts was
carried out by the ship's crew with OCEANS Ltd. personnel assisting.
General preparation of the Ovatek life rafts involved charging and changing out batteries as required
for the data loggers, lights and beacons. As well, life raft configurations were changed as necessary.
Wind speed and direction sensors were checked routinely and their correct operation confirmed.
Prior to departing for the deployment location the CR10X data loggers in the 4- and 7-person life
rafts were turned on to collect wind, temperature, GPS and life raft heading data while the
Orbcomm satellite communications systems were set up to communicate positional information
back to OCEANS Ltd. via email. As well, the InterOcean S4 current meters were set up and their
operation confirmed as were the ARGOS PTTs in each life raft. VHF beacons for each life raft
were turned on and their operation confirmed through the vessel’s VHF direction finder. The final
tasks prior to leaving port were securing the instrumentation and ballast inside the life rafts and then
locking down the hatches. Life rafts remained secured in their cradles until it came time to deploy
them.
25
Once at location, life raft deployment operations began. The life rafts were lifted over the side using
the ship's crane. Once the life raft was in the water, it was allowed to drift away from the vessel
while the S4 tether and drogue were payed out. Once deployed, a positional fix was taken. The
ship then moved away from the life raft in such a fashion so as not to disturb the natural drift of the
life raft. The vessel would then proceed to the next deployment location. The life rafts were
generally deployed between 0.25 and 0.50 nautical miles apart. The time required to deploy each
life raft was generally in the order of 10 minutes.
2.5.3
Tracking
After the life rafts were deployed the vessel returned to St. John's or stayed in the vicinity of the life
rafts overnight depending on the operational plan. While in St. John's the life raft positions were
monitored through the Orbcomm system and ARGOS network. If the support vessel remained
onsite the life rafts were visually and electronically monitored. Visual monitoring was normally
limited to checking the general condition of the life raft. Visual checks included such things as the
trim of the life raft, fouling of the S4 tether, confirmation that the S4 was attached, the lights were
working and so forth. Electronic monitoring of the life rafts included tracking on the vessel’s radar
and the use of direction finding equipment. Onboard the CCGS “Ann Harvey”, personnel were also
able to check the Orbcomm and ARGOS messages via a Globalstar Satellite connection.
2.5.4
Recovery
Prior to departing from St. John’s for recovery operations the latest positions were obtained from the
Orbcomm system and ARGOS. When the vessel departed St. John’s it proceeded to the general
location of the last known position. Normally, when the vessel arrived at this location the VHF
direction finder would be receiving the signal from the VHF beacon. Once the VHF beacon signal
was received it was simply a matter of steaming up to the life raft. An ARGOS PTT direction
finder was used as back up to the VHF beacon/direction finder system.
During recovery operations the life raft was normally approached from down wind. The first item
to be retrieved was the S4 tether. Once this was on board it was used to bring the life raft alongside
the rail while the S4 and drogue (if attached) were brought on board. Once alongside, the tag lines
of the life raft were grappled and brought on board and used to stabilize the load during recovery.
Once the life raft was stabilized the lifting hook of the crane was attached to the eye of the life raft
lifting harness. The life raft was then lifted onboard by the crane while control was maintained by
the tag lines. When lifted onboard the life rafts were lowered into their cradles where they were
26
lashed and secured. Ancillary equipment including the InterOcean S4, floats, beacons and tethers
were all stowed and secured while heading for the next life raft or prior to departing the site for St.
John’s. Downloading of data was carried out once the vessel tied up in St. John’s. All data
collected were downloaded to laptop computers with backups stored on CDROM discs. From there
certain plots of the data were generated and reviewed.
2.6
Leeway Determination
Ovatek leeway speeds and angles were determined directly using the InterOcean S4 current
meter during the Phase I and Phase II trials. Using the principle of an electromagnetic ship's log,
the current meter was tethered to the SAR object to measure velocity relative to the water. Tenminute vector averages based on half second sampling rates were logged. An internal electronic
Figure 2-25 InterOcean S4 Current Meter in Tow Frame
tilt-compensated compass provided direction reference. Leeway direction was given by the
reciprocal of the logged direction and the difference between the downwind and leeway
directions provided leeway angle. The S4 current meter was selected because of its stable
hydrodynamic characteristics and its ability to provide accurate current data in the wave zone.
The water drag of the current meter and tow frame was at least partially offset by the wind drag
on a 0.65 m float to which the frame was secured. The float size was determined from
calculations and tests conducted during previous leeway work (Fitzgerald et al., 1993). The
center of the current meter was 0.75 m below the sea surface.
27
3.0
DATA REDUCTION AND ANALYSIS METHODOLOGY
The following subsections discuss the data reduction and analysis procedures that were carried
out in this work.
3.1
Data Reduction
The data reduction process consisted of the following steps:
1. combine the data obtained at ten-minute intervals from the various data collection
systems into single ten-minute records
2. compute ten-minute averaged courses and speeds over the ground using the GPS position
data
3. correct life raft magnetic heading and direction data for magnetic variation using GPS
position information
4. correct the apparent wind velocity for the motion of the drift object over the ground
5. adjust the corrected wind velocity at the anemometer height to the standard reference
height of 10 m above the surface
6. quality control the data
For each drift object, leeway velocity data were obtained directly using a towed InterOcean S4
current meter that served as an electromagnetic log. In common with previous work, velocity
data, sampled at 2 Hertz, were vector averaged over 10-minute sampling periods. Since the
position of the drift objects could not be known in advance, no magnetic variation correction was
applied during data collection. Water temperature measurements were also recorded by the S4 at
10-minute intervals. Initial processing of these data was limited to the date and time stamping of
the individual 10-minute records, and to the computation of the reciprocal of the direction
measurement, since leeway direction is opposite the apparent ‘current’ direction that was
recorded. Later, when these data were combined with the other environmental data and the
position data, the leeway direction was corrected to true direction by applying magnetic
variation.
Wind velocity and platform heading data, sampled at 1 Hertz, were vector averaged over 10minute periods, while instantaneous air and near surface temperature measurements were logged
28
at 10-minute intervals. GPS positions were recorded at 5-minute intervals: one position was
logged along with the 10-minute environmental data measurements and the subsequent one at the
middle of the recording period. These data were smoothed using a 3-element running mean and
the smoothed values at the end of each 10-minute sampling period were used to calculate 10minute average courses and speeds over the ground. Using the GPS positions at the sample
times, the predicted magnetic variations for the September 2004 and November 2005 periods
were extracted from a file provided by the Geomagnetic Laboratory, Geological Survey of
Canada, Natural Resources Canada. These data were applied to correct the magnetic heading of
the life raft, the apparent magnetic wind direction, and the magnetic leeway direction to true
directions.
The true wind velocity (at the anemometer) was then computed as the vector sum of the true
apparent wind velocity and the true (smoothed) velocity of the life raft over the ground for each
ten-minute sample.
Finally, wind speed data were adjusted from the anemometer level to the standard 10 m reference
height using the stability-dependent surface boundary layer wind speed adjustment algorithm
described by Smith (1981). The required inputs for the speed adjustment routine include:
•
wind speed at the anemometer
•
the height of the anemometer above the water surface
•
the air temperature
•
the height of the air temperature sensor above the surface
•
the sea surface temperature
Note that within the surface boundary layer of the atmosphere, the wind direction is invariant
with height and no adjustment is necessary.
Smith (1988) discusses the limitations of the formulations for adjusting wind speeds in the
surface boundary layer in some detail. The limitations are:
1. the data on which the formulations are based are limited to wind speeds of 26 m/s (52
knots); consequently, application in higher wind speed must be viewed as an
extrapolation
29
2. in conditions of strong static stability and low wind speeds, turbulence cannot be
maintained and the solution of the formulations does not converge
3. the surface layer formulations are found to be valid at heights up to 65 m above the
surface
4. the formulations are not applicable in water depths less than 50 m, short fetches from the
shore, coast, or ice boundary, and in rapidly varying, transient wind conditions
During the September 2004 field program there were a few instances of highly stable surface
boundary conditions (item 2) for which the adjustment solution did not converge. For these few
cases, the 10-minute data samples were removed from the dataset.
Having made the various corrections and adjustments, the data were combined to produce
individual drift runs files of 10-minute sample records containing, in part:
•
date and time
•
latitude and longitude
•
platform heading
•
course and speed of the drifting platform over the ground
•
air and sea surface temperature
•
10 m wind speed and surface boundary layer wind direction
•
leeway speed and angle
•
downwind and crosswind leeway component speeds
A number of other observed parameters were included in the data files along with a few ratios
computed between various parameters. An important ratio is the sample leeway rate, the ratio of
the leeway speed to the 10 m height 10-minute wind speed. This ratio was used to help define
the period of good data, data for which the influences of deployment and recover activities are no
longer apparent.
An initial review and quality assessment of the data was then done by preparing time-series plots
of various parameters (sample leeway rate, and speeds and direction for example), scatter
diagrams of leeway speed against 10 m wind speed, and progressive vector diagrams of leeway
displacement. In addition, certain descriptive statistics were computed. The primary purpose of
this work was to assist in identifying apparent anomalies in the data and to assess whether the
apparent anomalies were real and, therefore, that the data are valid, or whether the irregularities
30
were a result of instrumentation problems or other possible affects such as changes of the drift
object configuration during the individual drift runs. In some instances during the 2004 field
program, unusually high apparent leeway speeds were recorded by the S4 current meter at the
beginning and end of a number of the drift runs, resulting in unrealistically high leeway rates.
These and other apparently anomalous data records were removed from the data files.
3.2
Summary of the Ovatek Life Raft Leeway Dataset
Table 3-1 provides a general summary of Ovatek life raft drift runs for which leeway data were
obtained. Configuration information, heights of the anemometer and air temperature sensors,
dates and times of the first and last good records are listed in each case. Duration is the length of
time in hours of the period of good data. These records are, in most cases, continuous. In some
instances, a number of spurious or erroneous data records were removed from the drift run data
files.
Table 3-1 Drift Run Data Collection Summary
2004 and 2005 Leeway Drift Experiments
Ovatek
Ballast
Drogue Sensor Heights
First Good Record
UTC Date and Time
Drift Size
Units
deployed Wind Temp
No. 4/7 80 kg/unit Yes/No
m
m
Year Mon Day Hr Mn
60
4
1
No
3.23
2.41 2004 09 07 19 50
61
7
1
No
3.25
2.41 2004 09 07 19 20
62
4
1
No
3.23
2.41 2004 09 09 19 50
63
7
1
No
3.25
2.41 2004 09 09 19 40
64
4
4
Yes
2.97
2.16 2004 04 12 20 00
65
7
7
Yes
3.04
2.20 2004 09 12 20 10
71
7
7
Yes
3.04
2.20 2005 10 28 19 50
72
4
4
Yes
2.97
2.16 2005 10 28 20 00
73
4
1
No
3.25
2.41 2005 11 02 14 00
74
7
1
No
3.25
2.36 2005 11 02 14 00
77
7
7
Yes
3.04
2.20 2005 11 16 16 00
78
4
1
No
2.73
1.91 2005 11 16 16 10
Last Good Record
UTC Date and Time Duration
Year Mon Day Hr Mn Hours
2004 09 08 10 30
14.67
2004 09 08 10 30
15.17
2004 09 10 11 10
15.33
2004 09 10 11 10
15.50
2004 09 13 11 40
15.67
2004 09 13 11 40
15.50
2005 10 30 18 40
38.00
2005 10 30 18 30
46.50
2005 11 03 00 40
10.67
2005 11 09 11 20 159.17
2005 11 19 16 40
69.50
2005 11 19 14 30
70.00
Note that the Campbell Scientific CR10X data logger used during drift run 73 was destroyed by
water ingress as a consequence of the capsizing of the life raft and subsequent damage. The S4
current meter, however, was recovered. Since GPS and ARGOS position reports show that the
7-person life raft used in drift run 74 was less than two nautical miles from the 4-person life raft
throughout the drift period, the wind data from drift run 74 was combined with the S4 data of
drift run 73 for analysis purposes.
31
Figure 3-1 and Figure 3-2 are plots showing the drift tracks for which data were recovered in
Phases I and II respectively.
Phase I General Operating Area
40'
35'
o
47 N
30.00'
Waverider
Start of Drift
End of Drift
DFT60 4-Person No Drogue 2004/09/07 19:50 to 2004/09/08 10:30
DFT64 4-Person Drogued 2004/09/12 20:00 to 2004/09/13 11:40
25'
20'
40'
30'
20'
Figure 3-1 Phase I Drift Tracks
32
10'
o
52 W
Phase II General Operating Area
48oN
40'
20'
47oN
MetBuoy
Waverider
Start of Drift
End of Drift
40'
53oW
30'
52oW
30'
51oW
30'
50oW
Figure 3-2 Phase II Drift Tracks
Table 3-2 provides a listing of the number of hours of data collection for the individual and
combined Ovatek life raft configurations, as well as the range of 10 m height wind speeds in
each instance. For the individual configurations, the duration ranged from 62 to 190 hours, least
for the 4-person life raft in the fully-loaded configuration, greatest for the 7-person lightly-loaded
configuration.
33
Table 3-2 Ovatek Life Raft Configuration Data Summary
Ovatek
Size
4
7
4
7
Load
Condition
Light/Full
Light*
Light
Full**
Full
Drogue
Yes/No
No
No
Yes
Yes
Wind Speed Range
at 10 m height
knots
1.3 - 36.5
4.6 - 33.7
1.8 - 26.6
2.7 - 30.5
4&7
Light
No
1.3 - 36.5
4&7
Full
Yes
1.8 - 30.5
* ballasted to represent one person on board
** ballasted to represent either 4 or 7 persons on board according to size of life raft
3.3
3.3.1
Duration
hours
110.7
189.8
62.2
123.0
300.5
185.2
Analysis Methodology
Definition of Leeway and Measurement Reference Levels
In this investigation, consistent with other recent leeway studies (Fitzgerald et al., 1994; Allen
and Plourde, 1999), leeway is defined as:
“Leeway is the velocity vector of the SAR object relative to the downwind
direction at the search object as it moves relative to the surface current as
measured between 0.3 and 1.0 m depth caused by the winds (adjusted to a
reference height of 10 m) and waves.”
3.3.2
Leeway Vectors
As a vector quantity, leeway may be expressed in the form of leeway speed and leeway angle off
the downwind direction or as downwind and crosswind leeway velocity components. Figure 3-3,
along with the accompanying equations, shows the graphical and mathematical relationships
between these forms. Note that leeway angle and the crosswind leeway component to the right
of the downwind direction are taken as positive, and vise versa.
3.3.3
Regression Models
The goal of the analysis work is to derive mathematical models for SAR object leeway that can
be used to accurately predict leeway velocity. Such models, to be operationally useful, need to
express leeway in terms of readily available predictors. Predictors should be physically related
34
to the predictand (SAR object leeway); for instance, wind velocity and, potentially, certain sea
state parameters. Ideally, model predictors should be independent of each other. From
theoretical considerations, leeway speed can be shown to be a linear function of wind speed.
Indeed, previous work (e.g., Fitzgerald et al., 1994) has shown that the relationship between
leeway speed and wind speed is highly linear and that, typically, the amount of variance
explained by wind speed in linear regression models (at zero lag) has often been found to be
greater than 0.90 (r2 > 0.90), given sufficient high quality data. Cross-correlation analysis has
shown that the correlations between leeway speed and wind speed are highest at zero lag
(Fitzgerald et al., 1993), indicating that the response time is within the sample averaging interval
of 10 minutes. From this, it is apparent that no other predictors other than an accurate estimate
of wind speed, either measured or forecast, is necessary to accurately estimate leeway speed.
35
North
V10m
CWL
DWL
Lα
L
East
V10m = Wind velocity vector adjusted to 10m height
L = Leeway vector
L α = Leeway angle
L
V10m
= Leeway rate
DWL = L sin(900 − L α ) = Downwind Leeway component
CWL = L cos(900 − L α ) = Crosswind Leeway component
Figure 3-3 Relationships Between Leeway Speed and Angle and the Downwind and
Crosswind Leeway Components
36
Two formulations of regression have been used in this work (linear regression and constrained
linear regression formulations) to model leeway speed as well as the downwind and crosswind
components of leeway on the 10 m wind speed. Linear regression is of form:
Vl = a + b * V10; for Vmin <= V10 <= Vmax
where:
Vl is the leeway speed in knots
a is the y-intercept
b is the slope of the regression line
V10 is the wind speed at 10 m above the sea surface (knots)
Vmin is the minimum 10 m wind speed in the development dataset (knots)
Vmax is the maximum 10 m wind speed in the development dataset (knots)
For the constrained linear regression model, the y-intercept value, a, is fixed at zero; otherwise
the model form is similar.
To assist in comparing model fits, certain statistics are provided along with each regression
model; in this work, they are:
•
The number of 10-minute samples in the development dataset (n).
•
The standard error of the estimate (Sy|x) is a measure of the scatter of the data about the
regression line with the same units as leeway (knots); typically, for a normal distribution
about the regression line, about 68% of actual leeway speeds would be expected to lie
within plus and minus one standard error from the regression value, and approximately
95% within plus and minus two standard errors.
•
The coefficient of correlation of the regression (r), a measure of the strength or degree of
association between the series (dimensionless, varying between -1 and +1).
•
The variance explained or accounted for (r2) by the regression model (dimensionless,
ranging from 0 to +1).
Neglecting any contribution due to wave action, leeway will be zero in calm wind conditions.
This can be modeled by forcing the linear regression formulation to pass through zero, the origin
37
on scatter diagrams of leeway speed and wind speed. Typically, the correlation of regression
will be lower and the standard error greater for the constrained linear regression model than with
the corresponding linear regression model fit to the data, since the fit to the data is typically
‘better’ as the number of model parameters is increased. With sufficient data, however, the
intercept of the linear regression model of leeway speed would be expected to be nearly zero and
the two regression models would, consequently, be very similar.
For each SAR object configuration investigated and certain combinations of SAR object
configurations, both linear regression and constrained linear regression models are presented for
leeway speed and leeway components. This will allow SAR incident controllers to use
whichever model he or she deems to be the most appropriate for the situation at hand.
Following previous work, leeway angle divergence off the downwind direction is presented
using basic descriptive statistics of the 10-minute measured values: typically, means and
standard deviations.
38
4.0
RESULTS AND DISCUSSION
This section contains leeway analysis results and discussion for 4- and 7-person Ovatek life rafts
deployed in the following two configurations:
1. lightly-loaded (ballasted to represent one person on board) without a drogue
2. fully-loaded (ballasted to represent 4- or 7-persons on board) with a drogue
These configurations represent limiting cases for these rigid life rafts. Configured according to
criteria 1, the life rafts have the greatest freeboard and lowest drag, and, therefore, would be
expected to have the highest leeway rates for these SAR objects. With the second configuration,
the life rafts have reduced ‘sail’ areas and significantly greater drag through the water, resulting
in the lowest anticipated leeway rates for the objects.
Individual configuration and some combined configuration results are discussed.
4.1
4.1.1
Lightly-Loaded Ovatek Life Rafts without Drogue
Leeway Speed
Figure 4-1 and Figure 4-2 are scatter diagrams of leeway speed and the corresponding 10 m wind
speed for the 4-person and 7-person Ovatek life rafts in the lightly-loaded no drogue
configuration, respectively. The linear trend line with regression model equation and r2 value are
also shown. Table 4-1 contains regression model results for both the linear regression and the
constrained linear models. In general, the variance explained by the regression models (r2) is
quite high and the scatter about the regression line, as indicated by the standard error statistic
(Sy|x), is seen to be quite small. The slopes (b) of the linear regression models are nearly
identical while for the constrained regression models, the slope of the 7-person life raft model is
greater than that of the 4-person model. Despite this, the models are not very different and it is
reasonable to combine the data for the 4- and 7-person lift rafts. A scatter plot of the combined
data is shown as Figure 4-3; the linear regression model coefficients and corresponding statistics
are tabulated in Table 4-1 along with the individual life raft configuration regression results.
39
Scatter Diagram of Leeway Speed and 10 m Wind Speed
Drift runs 060, 062, 073, and 078: Ovatek 4-Person Life Raft, lightly-loaded without drogue
1.6
1.4
1.2
40
Leeway Speed (knots)
y = 0.0383x + 0.0128
2
R = 0.9545
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
10m Wind Speed (knots)
Figure 4-1 Leeway Speed against 10 m Wind Speed - Ovatek 4-person life raft, lightly-loaded without drogue
Drift runs 061, 063, and 074: Ovatek 7-Person Life Raft, lightly-loaded without drogue
1.6
1.4
y = 0.0382x + 0.0795
2
R = 0.8367
41
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
Figure 4-2 Leeway Speed against 10 m Wind Speed - Ovatek 7-person life raft, lightly-loaded without drogue
Evidently, the best-fit regression model shows that the leeway speed of a lightly-loaded Ovatek
rigid life raft deployed without a drogue (either 4- or 7-person life raft) is 3.91 percent of the
wind speed (plus a constant of 0.0418 knots). The standard error is under 0.10 knots and the
variance accounted for by this model is 87.1 percent.
If, in a SAR incident involving an Ovatek life raft, the size of the Ovatek life raft is known, then
corresponding individual model(s) should be used to predict the leeway component of the drift.
Otherwise, if the size is unknown, then the model(s) for the 4- and 7-person life rafts combined
would be most appropriate.
The development dataset from which these models were developed included 10 m height wind
speeds ranging from very light winds to gale force winds. The strong linear correspondence
between leeway speed and wind speed suggests that these models could be used with good
confidence in 10 m winds to at least storm force (48 knots).
Table 4-1 Linear Regression Models of Leeway Speed on 10 m Wind Speed for Ovatek 4and 7-person Rigid Life Rafts, Lightly-loaded without Drogue
Ovatek
size
(persons)
4
7
4&7
(Wind Speed and Leeway Speed in knots)
Wind Speed
Linear Regression Model
Constrained Linear Regression Model
Range
n
a
b
Sy|x
r
r^2
a
b
Sy|x
r
r^2
(knots)
668 0.01282 0.03833 0.05068 0.97699 0.95451
0.0 0.03909 0.05089 0.97676 0.95407 1.3 - 36.5
1142 0.07948 0.03818 0.10492 0.91471 0.83669
0.0 0.04242 0.10860 0.90823 0.82488 4.6 - 33.7
1810 0.04180 0.03907 0.09396 0.93320 0.87087
0.0 0.04138 0.09521 0.93131 0.86733 1.3 - 36.5
42
Ovatek 4- and 7-Person Life Rafts, lightly-loaded without drogue
1.6
1.4
y = 0.0391x + 0.0418
2
R = 0.8709
43
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
Figure 4-3 Leeway Speed Against 10 m Wind Speed - Ovatek 4- and 7-person life rafts, lightly-loaded without drogue
4.1.2
Leeway Angle Divergence
4.1.3
Progressive Leeway Displacement Plots
Progressive leeway displacement plots of individual drift runs for lightly-loaded Ovatek life rafts
deployed without a drogue are shown in Figure 4-4. The leeway displacements are plotted as if
the wind direction was always from the south and serve to illustrate the range of divergence
angles off the downwind direction for the drift runs as a whole. Limiting divergence angles off
the downwind angle for this configuration are shown in the figure; they range between about
plus and minus 32º off the downwind direction. In some of the drifts, the leeway angle is seen to
change from positive to negative leeway angles rather suddenly; in other cases, more gradual
shifts are evident. This is more easily seen in the enlargement (Figure 4-5). Evidently, for this
configuration, the nature of leeway angle variability is different for the two sizes of life raft. The
angular divergence for the 4-person life raft is, in general, less than that of the 7-person life raft,
with relatively smaller changes of leeway angle rather than the more sudden, larger shifts (from
positive to negative angles, and vice versa) that is evident for the 7-person life raft, especially in
the early portion of drift run 74.
Examination of the time-series plots of the relative wind direction and leeway angle for the 4and 7-person Ovatek life rafts in this configuration show that the relative wind direction was
often quite close to abeam throughout the drift runs (see Figure 4-6 and Figure 4-7 for sample
plots). This occurred considerably more frequently in the case of the 7-person life raft, however.
When so oriented, the relative wind direction was generally slightly forward of the beam in the
case of the 4-person life raft and just abaft the beam for the 7-person life raft. In both cases, the
life rafts moved to the right of the downwind direction when the wind was on the port beam and
to the left of downwind with the relative wind on the starboard beam, but to a considerably
greater degree in the case of the 7-person Ovatek than the 4-person life raft. The round bottom
design of the 7-person life raft resulted in greater directionally stability than the flat-bottom 4person life raft when deployed without the controlling influence of a drogue. An example of the
more erratic behaviour of the 4-person life raft is evident in the life raft heading and relative
wind direction data shown at the left and right side of the sample time-series plot for the 4person life raft (Figure 4-6). These particular example periods both occurred during times of
backing winds; in these instances, leeway angles were generally of greater magnitude and
showed greater variability than during the periods when the life raft orientation was more stable.
44
Progressive Leeway Displacement
Ovatek Rigid Life Rafts - Lightly-loaded without drogue
(True wind direction rotated into south)
120
110
Drift 061 - Ovatek 4-person
100
Downwind Leeway Displacement (nm)
90
80
Angular limits +/- 32 degrees
70
60
50
40
30
20
10
0
-40
-30
-20
-10
0
10
20
30
40
Crosswind Leeway Displacement (nm)
Figure 4-4 Progressive Leeway Displacements: Ovatek 4- and 7-person Rigid Life Rafts,
45
Ovatek Rigid Life Rafts - Lightly-loaded without drogue
30
25
20
Ovatek 4-person life raft
Angular limits +/- 32 degrees
15
10
5
0
-10
-5
0
5
Figure 4-5 Progressive Leeway Displacements – enlarged scale
46
10
True Life Raft Heading and other parameters
Drift Run 078: 4-Person Ovatek, lightly-loaded without drogue
360
180
True wind direction
Life raft heading
Leeway angle
Relative wind direction
47
Wind Direction and Life Raft Heading
(degrees True)
300
150
120
270
90
240
60
210
30
180
0
150
-30
120
-60
90
-90
60
-120
30
-150
0
17/00
-180
17/03
17/06
17/09
17/12
17/15
17/18
17/21
18/00
18/03
18/06
18/09
18/12
18/15
November 2005
Figure 4-6 Sample Time-series Plot During Leeway Drift Run 078
18/18
18/21
19/00
Leeway Angle and Relative Wind Direction (degrees)
330
True Life Raft Heading and other parameters
Drift Run 074: 7-Person Ovatek, lightly-loaded without drogue
360
180
True wind direction
Life raft heading
Leeway angle
Relative wind direction
48
Wind Direction and Life Raft Heading
(degrees True)
300
150
120
270
90
240
60
210
30
180
0
150
-30
120
-60
90
-90
60
-120
30
-150
0
02/12
-180
02/15
02/18
02/21
03/00
03/03
03/06
November 2005
Figure 4-7 Time-series Plot at the Start of Drift Run 074
03/09
03/12
Leeway Angle and Relative Wind Direction (degrees)
330
Abrupt shifts of leeway angle from positive to negative values, and vice versa, during the
beginning stages of drift run 074 tended to occur at times of backing or veering of the wind,
including relatively small direction changes at times. Not all instances of backing or veering
winds resulted in such shifts, however. An examination of time-series of directional wave data
using APLwaves sea state partitioning software did not show any indication that changes of sign
of leeway angle were dependent on wave direction variability. The wave data were not
measured in the immediate vicinity of the life raft, however.
4.1.2.2 Leeway Angle Statistics
Figures 4.8 and 4.9 are scatter plots of the leeway angle and 10 m wind speed for 4-person and 7person Ovatek life rafts in the lightly-loaded no drogue configuration, respectively. These 10minute sample data also show that the nature of leeway angle for the 7-person Ovatek life raft is
radically different than that of the 4-person life raft, particularly for 10 m wind speeds of 12 to
15 knots and higher. At these speeds, the 4-person life raft leeway angle data show the scatter
concentrating between about +/- 15º from the downwind direction. In the case of the 7-person
Ovatek, a bifurcation in the scatter pattern is evident above about 15 knots with a tendency
toward plus or minus 30º, approximately, as wind speeds increase further. Leeway angle
statistics are presented in Table 4-2. For the 4-person life raft and for the 4- and 7-person life
rafts combined, the mean leeway angle and standard deviation are given. For the 7-person
Ovatek, the overall mean and standard deviation are listed along the positive and negative
leeway angle means and associated standard deviations. The 10 m height wind speed ranges are
also provided in the table.
Table 4-2 Leeway Angle Statistics - Ovatek 4- and 7-person Rigid Life Rafts Lightly-loaded
without Drogue
Ovatek
(persons)
4
7
4&7
Statistic
Average
Standard deviation
Average
Standard deviation
Average (pos angle)
Std dev (pos angle)
Average (neg angle)
Std dev (neg angle)
Average
Standard deviation
Leeway Angle
(degrees)
-2.6
12.8
-11.4
18.6
15.1
9.0
-19.4
12.3
-8.2
17.2
49
Wind Speed Range
(knots)
1.3 - 36.5
Number of
10-minute Samples
668
4.6 - 33.7
1142
4.6 - 30.3
265
4.6 - 33.9
877
1.3 - 36.5
1810
Scatter Diagram of Leeway Angle and 10 m Wind Speed
Ovatek 4-person Life Raft, lightly-loaded without drogue
-90
Leeway Angle (degree, positive to right of downwind)
-75
-60
-45
-30
-15
0
15
30
45
60
75
90
0
5
10
15
20
25
30
35
40
10 m Wind Speed (knots)
Figure 4-8 Leeway Angle and Wind Speed, Ovatek 4- person Life Raft, Lightly-loaded
without drogue
50
Ovatek 7-person Life Raft, lightly-loaded without drogue
-90
-75
-60
-45
-30
-15
0
15
30
45
60
75
90
0
5
10
15
20
25
30
35
40
Figure 4-9 Leeway Angle and Wind Speed, Ovatek 7-person Life Rafts, Lightly-loaded
without drogue
4.1.4
Downwind and Crosswind Leeway Components
Downwind and crosswind leeway component data for lightly-loaded Ovatek 4- and 7-person
rigid life rafts without a drogue are presented in Figure 4-10 through Figure 4-15. Two plots are
shown for the each of the individual Ovatek life raft sizes as well as for the 4- and 7-person life
rafts combined. The first graph is a scatter plot of downwind leeway speed against the 10 m
wind speed; it also shows the linear regression model fit to the data. Positive and negative
crosswind leeway components and 10 m wind speed data are shown in the second figure;
constrained linear regression models fit to the positive and negative subsets are also shown.
Regression model parameters and statistics for both the linear regression models and
constrained regression models are presented in
Table 4-3. Model fit is very good for the downwind leeway component for the 4-person life raft
but somewhat less so for the 7-person Ovatek where there is greater scatter in the data. The
intercept value is rather larger than desirable, as well. The best fit linear regression models for
the downwind components show the slope of the model for the 4-person life raft to be greater
than that of the Ovatek 7-person life raft in this configuration.
51
The variance accounted for by the low slope crosswind leeway component models is relatively
low but the magnitude of the standard errors is about the same as that of the corresponding
downwind component model. Constrained regression model results show that the crosswind
leeway component is approximately +/- 0.5 to 0.6 percent of the 10 m wind speed for the 4person life raft and +/- 1.4 to 1.5 percent for the 7-person life raft, qualitatively as expected from
the discussion of leeway angle.
Crosswind models using the absolute value of the crosswind speed component are also
given in the
Table 4-3. These models combine the positive and negative crosswind data as ‘weighted’ mean
crosswind leeway models applicable to both the left and right of the downwind direction.
Assuming that the true crosswind leeway component is symmetrical for these life rafts, the real
error in the combined crosswind models may be less than that of the corresponding positive and
negative crosswind leeway models.
52
Scatter Diagram of Downwind Leeway Speed and 10 m Wind Speed
Drift runs 060, 062, 073, and 078: Ovatek 4-Person Life Raft, lightly-loaded without drogue
1.6
1.4
y = 0.0386x + 0.0002
53
Downwind Leeway Speed (knots)
2
R = 0.95
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
Figure 4-10 Downwind Leeway - Ovatek 4-person Rigid Life Raft, Lightly-loaded without Drogue
40
Scatter Diagram of Crosswind Leeway Speed and 10 m Wind Speed
Drift run 060, 062, 073, and 078: Ovatek 4-Person Life Raft, lightly-loaded without drogue
-1.0
-0.8
54
Crosswind Leeway Speed (knots)
-0.6
-0.4
y = -0.0049x
-0.2
0.0
0.2
y = 0.0048x
0.4
0.6
0.8
1.0
0
5
10
15
20
25
30
35
Figure 4-11 Crosswind Leeway - Ovatek 4-person Life Raft, Lightly-loaded without Drogue
40
1.6
1.4
y = 0.0326x + 0.1197
2
R = 0.7105
55
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
Figure 4-12 Downwind Leeway - Ovatek 7-person Rigid Life Raft, Lightly-loaded without Drogue
40
-1.0
-0.8
y = -0.015x
2
R = 0.5664
56
-0.6
-0.4
-0.2
0.0
0.2
0.4
y = 0.0138x
2
R = 0.4678
0.6
0.8
1.0
0
5
10
15
20
25
30
35
Figure 4-13 Crosswind Leeway - Ovatek 7-person Rigid Life Raft, Lightly-loaded without Drogue
40
1.6
1.4
y = 0.0351x + 0.0678
57
2
R = 0.7986
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
Figure 4-14 Downwind Leeway - Ovatek 4- and 7-person Rigid Life Rafts, Lightly-loaded without Drogue
-1.0
-0.8
y = -0.0124x
2
R = 0.4067
58
-0.6
-0.4
-0.2
0.0
0.2
0.4
y = 0.0092x
2
R = 0.2348
0.6
0.8
1.0
0
5
10
15
20
25
30
35
Figure 4-15 Crosswind Leeway- Ovatek 4- and 7-person Rigid Life Raft, Lightly-loaded without Drogue
40
Table 4-3 Downwind and Crosswind Regression Models for Lightly-loaded Ovatek 4- and 7-person Life Rafts without Drogue
b
Sy|x
r
r^2
a
b
Sy|x
r
r^2
0.03859 0.05362 0.97468 0.95000 0.0 0.03860 0.05358 0.97468 0.95000
0.00250 0.05348 0.27281 0.07443 0.0 0.00487 0.05565 -0.06190 0.00383
0.00323 0.05095 0.36330 0.13198 0.0 0.00482 0.05198 0.30537 0.09325
-0.00187 0.05471 -0.19893 0.03957 0.0 -0.00489 0.05793 -0.28158 0.07929
Downwind component
Crosswind component
Positive crosswind
Negative crosswind
Ovatek
size
(persons)
4
4
4
4
n
668
668
260
408
Downwind component
Crosswind component
Positive crosswind
Negative crosswind
7
7
7
7
1142
1142
265
877
0.11969 0.03257
-0.11942 0.02122
-0.14258 0.02323
0.11700 -0.02101
0.12934 0.84289
0.10157 0.79249
0.09272 0.75791
0.10403 -0.78959
0.71046
0.62804
0.57442
0.62345
0.0 0.03896
0.0 0.01485
0.0 0.01376
0.0 -0.01505
0.13607
0.11001
0.10350
0.11158
0.82416
0.75053
0.68394
0.75258
0.67923
0.56329
0.46777
0.56637
4.6- 33.7
4.6- 33.8
4.6 - 29.6
4.6 - 33.7
Downwind component
Crosswind component
Positive crosswind
Negative crosswind
4&7
4&7
4&7
4&7
1810
1810
525
1285
0.06782 0.03510
-0.07948 0.01612
-0.02421 0.01079
0.09088 -0.01721
0.11007 0.89366
0.11810 0.64883
0.10404 0.49053
0.12128 -0.66829
0.79863
0.42098
0.24062
0.44661
0.0 0.03885
0.0 0.01173
0.0 0.00923
0.0 -0.01241
0.11289
0.12171
0.10434
0.12552
0.88772
0.62023
0.48454
0.63775
0.78805
0.38469
0.23478
0.40673
1.3 - 36.5
1.3 - 36.5
1.3 - 29.6
2.0 - 36.5
Leeway Model
a
0.00022
0.03966
0.02553
-0.05188
Wind Speed
Range
(knots)
1.3 - 36.5
1.3 - 36.5
1.3 - 24.9
2.0 - 36.5
59
4.2
4.2.1
Fully-Loaded Ovatek Life Rafts with Drogue
Leeway Speed
Figure 4-16 and Figure 4-17 are scatter plots of leeway speed against the corresponding 10 m
wind speed for the 4- and 7-person Ovatek life rafts deployed fully-loaded with a drogue,
respectively. Figure 4-18 is a scatter plot of the 4- and 7-person Ovatek data combined. Note
that the scale of the plots is the same as for the lightly-loaded no drogue configuration plots
shown previously. The best-fit linear regression model is also shown on each plot. Regression
model coefficients and associated statistics are presented in Table 4-4. The effect (and
efficiency) of the drogue is readily evident by the slopes (b) of the regression models in
comparison with the models for lightly-loaded life rafts without drogues (see Table 4-1). For
example, the linear regression model for the combined data sets has a slope of 0.010 compared
with 0.0391 for the lightly-loaded no drogue configuration. Leeway speed for this configuration
is therefore about 1.0 percent of wind speed compared with 3.9 percent (plus the corresponding
intercept values) for the other configuration. The wind speed ranges in the development datasets
were less than for light-loaded no drogue drift runs, but the models are expected to provide a
good estimate of the leeway speeds for 10 m height wind speeds to at least storm force.
Table 4-4 Linear Regression Models of Leeway Speed on 10 m Wind Speed for Ovatek 4and 7-person Rigid Life Rafts, Fully-loaded with Drogue
Ovatek
size
(persons)
4
7
4&7
Wind Speed
Range
n
a
b
Sy|x
r
r^2
a
b
Sy|x
r
r^2
(knots)
373 0.04920 0.01085 0.03037 0.92041 0.84716
0.0 0.01388 0.03770 0.87401 0.76389 1.8 - 26.9
741 0.07627 0.00969 0.04431 0.81924 0.67115
0.0 0.01405 0.05416 0.71271 0.50796 2.7 - 30.5
1114 0.06533 0.01018 0.04067 0.85528 0.73151
0.0 0.01400 0.04926 0.77830 0.60576 1.8 - 30.5
60
Drift runs 064 and 072: Ovatek 4-Person Life Raft, fully-loaded with drogue
1.6
1.4
61
1.2
1.0
0.8
y = 0.0108x + 0.0492
2
R = 0.8472
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
Figure 4-16 Leeway Speed against 10 m Wind Speed – Ovatek 4-person Rigid Life Raft, Fully-loaded with Drogue
Drift runs 065, 071, and 077: Ovatek 7-Person Life Raft, fully-loaded with drogue
1.6
1.4
62
1.2
1.0
0.8
y = 0.0097x + 0.0763
2
R = 0.6711
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
Figure 4-17 Leeway Speed against 10 m Wind Speed – Ovatek 7-person Rigid Life Raft, Fully-loaded with Drogue
Ovatek 4- and 7-Person Life Rafts, fully-loaded with drogue
1.6
1.4
63
1.2
1.0
0.8
y = 0.0102x + 0.0653
2
R = 0.7315
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
40
Figure 4-18 Leeway Speed against 10 m Wind Speed – Ovatek 4- and 7-person Rigid Life Raft, Fully-loaded with Drogue
4.2.2
Leeway Angle Divergence
4.2.2.1 Progressive Leeway Displacement
Progressive leeway displacement plots for individual drift runs of fully-loaded life rafts with a
drogue are shown in Figure 4-19. They are plotted as if the wind direction was continuously
from the south and show that the excursion off the downwind direction was generally quite
limited for both the 4- and 7-person life rafts. An exception occurred near the beginning of drift
run 064 were the drift angle off the downwind direction near the start of the run was as high as 39º (to the left of downwind) for a short period of time (for two 10-minute sample periods only,
in fact). The greatest angular divergence to the right of the downwind direction was found to be
about 20º. The end-of-run angles off the downwind direction (again, assuming constant wind
direction) ranged from -1.4º to +10.0º for the five drift runs.
4.2.2.2 Leeway Angle Statistics
Figure 4-20 is a scatter diagram showing the 10-minute samples data of leeway angle against the
10 m wind speed for the fully-loaded life rafts with a drogue. Less scatter is evident in the data
for wind speeds of above about 15 knots. Average leeway angles and corresponding standard
deviations are given in Table 4-5 for the two life raft sizes individually and for the 4-person and
7-person life rafts combined. For the combined datasets, the mean leeway angle was found to be
+6.5º, with a standard deviation of 12.5º. Assuming a normal distribution, 68 percent of leeway
angles would be expected to lie within +/- 12.5º and 95 percent within /- 25º, approximately.
Table 4-5 Leeway Angle Statistics - Ovatek 4- and 7-person Life Rafts, Fully-loaded With
Drogue
Ovatek
(persons)
4
7
4&7
Statistic
Average
Standard deviation
Average
Standard deviation
Average
Standard deviation
Leeway Angle
(degrees)
0.6
12.3
9.5
11.5
6.5
12.5
64
Wind Speed Range
(knots)
1.8 - 26.9
Number of
10-minute Samples
373
2.7 - 30.5
741
1.8 - 30.5
1114
Ovatek Rigid Life Rafts - Fully-loaded with drogue
15
Negative limit -39 degrees
Positive limit +20 degrees
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
-5
-4
-3
-2
-1
0
1
2
3
4
5
Figure 4-19 Progressive Leeway Displacements: Ovatek 4-and 7-person Rigid Life Rafts,
Fully-loaded with Drogue
65
Ovatek 4- and 7-person Life Rafts, fully-loaded with drogue
-90
66
-75
-60
-45
-30
-15
0
15
30
45
60
75
90
0
5
10
15
20
25
30
35
40
Figure 4-20 Leeway Angle Scatter Plot - Ovatek 4- and 7-person Life Rafts, Fully-loaded with Drogue
4.2.3
Downwind and Crosswind Leeway Components
Figure 4-21 is a scatter plot showing downwind leeway component against the 10 m wind speed
for the 4-person Ovatek life raft fully-loaded with a drogue. The best fit linear regression model
is also shown. The scatter plot of the positive and negative crosswind leeway components and
10 m wind speed is presented as Figure 4-22; constrained linear regression models are shown as
well. The model parameters and associated statistics are detailed in Table 4.6. Figure 4-23 and
Figure 4-24 are similar scatter plots for the 7-person Ovatek life rafts having the same
configuration. While all of slopes of the crosswind models are very small, the linear regression
analysis of the absolute crosswind leeway component for the 7-person life raft resulted in an
extremely small slope and effectively zero amount of variance explained; as a consequence, no
model parameters for this data subset are given in Table 4-6.
Downwind and crosswind component models for the two life raft sizes are sufficiently similar
that the results can be readily combined. The downwind leeway component data scatter and best
fit linear regression model for the 4-person and 7-person life raft are shown in Figure 4-25 while
the corresponding crosswind component data and associated constrained linear regression
models are illustrated in Figure 4-26. Table 4-6 lists the model parameters for the combined
datasets.
67
1.6
68
1.4
1.2
1.0
0.8
0.6
y = 0.0109x + 0.0449
2
R = 0.8447
0.4
0.2
0.0
0
5
10
15
20
25
30
35
Figure 4-21 Downwind Leeway - Ovatek 4-person Rigid Life Raft, Fully-loaded with Drogue
40
-1.0
-0.8
69
-0.6
-0.4
y = -0.0017x
-0.2
0.0
0.2
y = 0.0014x
0.4
0.6
0.8
1.0
0
5
10
15
20
25
30
35
Figure 4-22 Crosswind Leeway - Ovatek 4-person Rigid Life Raft, Fully-loaded with Drogue
40
1.6
70
1.4
1.2
1.0
0.8
y = 0.0099x + 0.0672
2
R = 0.6707
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
Figure 4-23 Downwind Leeway - Ovatek 7-person Rigid Life Raft, Fully-loaded with Drogue
40
-1.0
-0.8
71
-0.6
-0.4
y = -0.0009x
-0.2
0.0
0.2
y = 0.0023x
0.4
0.6
0.8
1.0
0
5
10
15
20
25
30
35
Figure 4-24 Crosswind Leeway - Ovatek 7-person Rigid Life Raft, Fully-loaded with Drogue
40
1.6
72
1.4
1.2
1.0
0.8
y = 0.0104x + 0.0582
2
R = 0.7303
0.6
0.4
0.2
0.0
0
5
10
15
20
25
30
35
Figure 4-25 Downwind Leeway - Ovatek 4- and 7-person Rigid Life Rafts, Fully-loaded with Drogue
40
-1.0
-0.8
73
-0.6
-0.4
y = -0.0013x
-0.2
0.0
0.2
y = 0.0021x
0.4
0.6
0.8
1.0
0
5
10
15
20
25
30
35
Figure 4-26 Crosswind Leeway - Ovatek 4- and 7-person Rigid Life Rafts, Fully-loaded with Drogue
40
Table 4-6 Downwind and Crosswind Regression Models - Ovatek 4- and 7-person Life Rafts, Fully-loaded with Drogue
Downwind component
Crosswind component
Positive crosswind
Negative crosswind
Ovatek
size
(persons)
4
4
4
4
Downwind component
Crosswind component
Positive crosswind
Negative crosswind
7
7
7
7
Downwind component
Crosswind component
Positive crosswind
Negative crosswind
4&7
4&7
4&7
4&7
Model Parameter
n
373
373
202
171
a
0.04489
0.01753
0.01865
-0.01539
74
741 0.06717
741
625 0.03623
116 -0.01853
1114
1114
827
287
b
Sy|x
r
r^2
a
b
Sy|x
r
r^2
0.01094 0.03093 0.91907 0.84469 0.0 0.01371 0.03703 0.88136 0.77679
0.00045 0.02238 0.13023 0.01696 0.0 0.00153 0.02373 -0.32910 0.10831
0.00027 0.01934 0.09867 0.00974 0.0 0.00139 0.02124 -0.44826 0.20094
-0.00071 0.02548 -0.16848 0.02838 0.0 -0.00169 0.02624 -0.19176 0.03677
0.00995 0.04554
0.81896 0.67070
0.00023 0.02566
0.00005 0.01701
0.05887 0.00347
0.01920 0.00037
0.05822 0.01036
0.02788 0.00028
0.03058 0.00034
-0.01875 -0.00021
0.04153 0.85458
0.02540 0.07304
0.02532 0.08885
0.02284 -0.06047
0.73030
0.00533
0.00789
0.00366
Wind Speed
Range
(knots)
1.8 - 26.6
1.8 - 26.6
1.8 - 26.2
3.8 - 26.6
0.0 0.01379
0.0 0.00207
0.0 0.00234
0.0 -0.00093
0.05316 0.74212 0.55074
0.02960 -0.56546 0.31974
0.02972 -0.58218 0.33893
0.01826 -0.40118 0.16095
2.7 - 30.5
2.7 - 30.5
2.7 - 30.5
4.1 - 27.3
0.0 0.01376
0.0 0.00191
0.0 0.00213
0.0 -0.00130
0.04835 0.79630 0.63409
0.02803 -0.46062 0.21217
0.02853 -0.51060 0.26071
0.02408 -0.33311 0.11096
1.8 - 30.5
1.8 - 30.5
1.8 - 30.5
3.8 - 27.3
5.0
CONCLUSIONS
The two phase project to evaluate the leeway characteristics of 4- and 7-person Ovatek rigid life
rafts has been successfully completed. Ovatek life rafts have become popular alternatives to
inflatable life rafts on fishing vessels longer than about 45 feet (13.5 m) in Atlantic Canada.
While the above water portion of the two sizes of rigid life rafts is quite similar in design, the
underwater configurations are significantly different. The 4-person life raft is flat-bottomed and
equipped with two nylon ballast bags to enhance its stability. The 7-person Ovatek life raft is
round-bottomed with an internal auto-filling water ballast cavity. The design differences were
expected to result is somewhat different leeway characteristics. Both sizes of life raft were
equipped by the manufacturer with identical drogue and rode assemblies, which require manual
deployment by life raft occupants when required. The drogues are relatively large compared
with the drogues typically supplied with inflatable life rafts of the same capacities and therefore
were expected to be functionally more efficient.
As in previous work conducted by OCEANS Ltd., leeway field trials were carried out on each of
the Ovatek life raft sizes in their limiting configurations:
1. lightly-loaded (equivalent of one person on board) without a drogue
2. fully-loaded (ballasted to represent 4 or 7 persons on board) with a drogue.
The first configuration, with greater freeboard (sail area) and less drag would be expected to
have the highest leeway speeds while the latter configuration, with reduced freeboard and much
greater drag through the water, would be expected to have the lowest leeway speeds for these
SAR objects.
A total of twelve Ovatek drift run trials were conducted with durations ranging from 11 to 159
hours. The data from the individual drift runs were combined resulting in configuration drift run
durations between 62 and 190 hours for the four different configurations. Ten metre height wind
speeds varied from very light to strong to gale force during the trials. Table 3-2 provides a
summary of the durations and wind speed ranges for each of the configurations as well as for the
combined configurations that were assessed.
The results of the leeway analyses have been presented in two forms. Linear regression models
have been developed for leeway speed and descriptive statistics provided for leeway angle
75
divergence. This is the form currently used by the Canadian Coast Guard as described in the
National SAR Manual (DF0, 1998) and implemented in CANSARP. The leeway characteristics
of SAR objects may also be presented in the form of downwind and crosswind leeway
components. This method is presently employed by the USCG and has the advantage that the
downwind and crosswind statistical models used in combination provide complete information
about the SAR object leeway vector, and include a measure of the scatter about the regression
models in the form of standard error statistics. For individual configurations and for certain
combinations of configurations, crosswind component data to the left and right of the downwind
directions have been combined resulting in ‘absolute’ crosswind component models, equally
valid to the left and right of the downwind direction. These models may in fact be more
representative of the true crosswind leeway component than the individual models to the left and
right of downwind, although the scatter about the regression model will be greater. Linear
regression models and linear models constrained to pass through zero have been developed in
each case.
There is sufficient confidence in the results to state the following conclusions about the leeway
characteristics of the Ovatek life rafts.
For lightly-loaded Ovatek life rafts deployed without a drogue:
1. Leeway rates and downwind leeway rates are sufficiently similar, at about 3.9 percent of
the 10 m wind speed, that the data can been combined to provide linear models that are
representative for the two life raft sizes.
2. Leeway angle divergence characteristics of the 4- and 7-person life rafts are markedly
different; as a consequence, leeway angle statistics and crosswind leeway components
models have been developed for each size of life raft.
For fully-loaded Ovatek life rafts deployed with a drogue:
The controlling influence of the drogue is sufficiently strong that the leeway data may be
combined to generate leeway speed models, leeway angle statistics, and downwind and
crosswind leeway velocity component models, that are representative for both sizes of life
raft. For this configuration, leeway rates are about one percent of the 10 m wind speed.
76
Details of the leeway speed models, leeway angle statistics, and downwind and crosswind
leeway component models are given in Table 4-1 through Table 4-6 in this report. The models
are expected to be valid for 10 m wind speeds up to storm force winds of 50 knots.
6.0
RECOMENDATIONS
1. Leeway Speeds and Angles
It is recommended that the Canadian Coast Guard, when planning SAR missions in wind speeds
up to 50 knots for 4- and/or 7-person Ovatek life rafts, use the leeway models shown in Table
4-1 through Table 4-6.
2. Leeway Model Validation
It is recommended as a follow up to the collection of leeway data for the 4- and 7- person Ovatek
life rafts that a validation of the derived leeway models be carried out. The purpose of the
validation would be (1) to confirm the reliability of the leeway models recommended in this
report and (2) demonstrate, by using reliable leeway models based on field research, the
improvement that can be obtained in SAR performance as it relates to finding a SAR object
faster and thus increasing the chances of saving lives which is the ultimate goal of this research.
The above can be accomplished by conducting several real time exercises for free drifting uninstrumented Ovatek life rafts. When the free drifting life rafts are deployed search plan
guidance would be used to predict the most probable area for finding the target. At the
conclusion of the exercises an assessment would be made on the search planning performance
with the benefit of the leeway models derived from the Ovatek leeway and drift trials.
3. Conduct Probability of Detection (POD) Trials for Ovatek Life Rafts
It is recommended that a Probability of Detection Exercise be carried for 4- and 7-person Ovatek
life rafts. This work would be a logical extension in completing the collection of SAR data for
the 4- and 7-person Ovatek life raft. It is recommended that the data be collected by an all
weather SAR vessel during poor weather which is the more common scenario when there is a
marine emergency on Canada’s East Coast.
Note: Recommendations 2 and 3 could be carried out in parallel.
77
4. Modify the Rode for Sea Anchor on the Ovatek Life Raft
It is recommended that the rode for the sea anchors presently being used with the Ovatek 4- and
7-person Ovatek life raft be modified to reduce the effects of the dynamic loading on the rode.
Observations made during the Phase I and II field trials first of all showed that this sea anchor is
very efficient. However, it was noticed that the rode of the sea anchor after only a 24 hour
period, in relatively light sea conditions, began to fray. It was felt that the constant tugging of
the rode against the rigid hull of the Ovatek life rafts would eventually lead to rode failure.
5. Determine the Leeway of Fully Loaded Ovatek Life Rafts without a Sea Anchor
It is recommended that a short project be carried out to determine the leeway characteristics of
fully loaded 4- and 7-person life rafts without a sea anchor deployed. The sea anchor has to be
attached and deployed by the persons in the life raft. Depending on the evacuation
circumstances this may or may not take place. Coupled with the discussion raised in
recommendation 4, there is a reasonable probability that during a SAR mission for an Ovatek life
raft that the configuration could well be a full life raft drifting without a sea anchor.
6. Investigate the Use of New Technologies for Leeway Determination
It is recommended that future leeway experiments investigate the use of new technologies and
methods for leeway determination. These should focus on reducing the influence of
instrumentation on leeway determination to zero.
78
7.0
References
Allen, A.A. and J.V. Plourde, 1999. Review of Leeway: Experiments and Implementation. US
Department of Transportation, US Coast Guard, CG-D-08-99, Washington.
DFO, 1998. National Search and Rescue Manual. B-GA-209-001/FP-001, DFO 5449.
Department of Fisheries and Oceans, Ottawa.
Dobson, F.W., 1981. Review of reference height for and averaging time of surface wind
measurements at sea. Rep. No. 3, Marine Meteorology and Related Oceanographic Activities,
WMO.
Fitzgerald, R., D.J. Finlayson, and A. Allen, 1994. Drift of Common Search and Rescue
Objects. Publication prepared for the Canadian Coast Guard. Transport Canada, Pub. No. TP
12179, Ottawa.
Smith, S.D., 1981. Factor for adjustment of wind speed over water to a 10 m height. Rep BI-R821-3, Bedford Institute of Oceanography, Dartmouth, N.S.
Smith, S.D., 1988. Coefficients for sea surface stress, heat flux, and wind profiles as a function
of wind speed and temperature. J. Geo. Res., 93, C12, pp 15467-15472.
79

Investigation of leeway and drift for Ovatek life rafts

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