[Federal Register Volume 60, Number 21 (Wednesday, February 1, 1995)]
[Notices]
[Pages 6345-6347]
From the Federal Register Online via the Government Publishing Office [www.gpo.gov]
[FR Doc No: 95-2493]
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DEPARTMENT OF TRANSPORTATION
Coast Guard
[CGD 91-202]
RIN 2115-AE10
Escort Vessels for Certain Oil Tankers
AGENCY: Coast Guard, DOT.
ACTION: Notice of availability.
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SUMMARY: A two-part study assessing the capability of escort tugs to
control disabled tankers in Prince William Sound, Alaska, was
commissioned by the Disabled Tanker Towing Study Group. The study
specifically reviewed the present equipment, personnel, and procedures
aboard the tankers and escort vessels operating in Prince William
Sound, as well as the assist capabilities of the vessels presently in
service for escorting these tankers. Both parts of the study have now
been completed, and the U.S. Coast Guard has been granted permission to
make it available to the public through the National Technical
Information Service (NTIS).
ADDRESSES: The study is published as two separate parts, which may be
ordered from the National Technical Information Service, Springfield,
VA 22161 (phone orders (703) 487-4650; MasterCard, Visa, and American
Express are accepted).
FOR FURTHER INFORMATION CONTACT: Thomas Jordan, Project Manager, OPA 90
Staff, at U.S. Coast Guard Headquarters, 2100 Second Street, SW.,
Washington, DC 20593-0001, or by phone at (202) 267-6751.
[[Page 6346]]
SUPPLEMENTARY INFORMATION:
Background
In the aftermath of the EXXON VALDEZ grounding, the state of Alaska
established a contingency plan that includes provisions requiring laden
tankers to be escorted through Prince William Sound. The escort vessels
are expected to provide immediate assistance to a tanker in the event
it suffers a propulsion or steering failure. The escort vessels also
have some spill response capabilities. At present, there are 11 tugs
and escort vessels in this service, operating out of Port Valdez and
escorting tankers to Hinchinbrook Entrance.
The Disabled Tanker Towing Study Group (DTTSG) was formed to review
the present escort vessel practices in Prince William Sound. The DTTSG
is formed of representatives from the Regional Citizen's Advisory
Council (RCAC) for Prince William Sound, the Prince William Sound
Tanker Association, the Alyeska Pipeline Service Company, the Alaska
Department of Environmental Conservation, and the U.S. Coast Guard.
The DTTSG commissioned The Glosten Associates, Inc., to prepare a
two-part study. The first part conducted an expert review and
evaluation of the emergency towing equipment aboard the tankers and
escort vessels operating in Prince William Sound. The second part
determined, by means of actual tanker/tug trials and computer
simulation analyses, the capabilities of the escort vessels to actually
control disabled tankers within the navigational limits of Prince
William Sound, under various weather and operating conditions.
Part 1 of the study was previously announced in a notice of
availability published by the Coast Guard (59 FR 1411; January 10,
1994). This present notice announces the availability of Part 2 of the
study.
Ordering Information
A synopsis of each part of the study is given here in order to
provide the public with an overview of the study and its findings.
Persons interested in obtaining full copies of the study may order it
from the National Technical Information Service. The NTIS publication
number for Part 1 of the study is PB94-120961 (price $27.00 for paper
copy, or $12.50 for microfiche copy). The publication number for Part 2
is PB95-147617 (price $119.00 for paper copy, or $52.00 for microfiche
copy). A separate shipping and handling charge of $8.00 per order also
applies. It generally takes 3 to 6 weeks to fill an order, unless a
customer opts to pay for 24-hour turnaround.
Summary of Part 1
Part 1 of the DTTS, entitled ``Evaluation of Existing Equipment,
Personnel and Procedures,'' is summarized as follows:
The DTTS is an objective evaluation by an experienced salvage
towing master of the existing tugs, emergency towing equipment, towing
practices, and discussion of alternate tug types.
The Part 1 investigation was performed by subcontractor Smit Tak
BV, based in Rotterdam. Captain Jan ter Haar, a senior Smit Tak salvage
master, conducted interviews and observed normal operations and
emergency drills in the Valdez area.
All tankers calling at Valdez are required to carry specific
emergency towing gear for rapid deployment and connection to a rescue
tug. This ``Prince William Sound Emergency Towing Package'' is stowed
and deployed differently on various vessels. Captain ter Haar
recommends that all vessels adopt systems that can be readied for
deployment in 15 minutes or less by a crew of two without using winch
power.
Captain ter Haar demonstrated, in drills, several effective
alternative methods of making towing connections with the tugs' own
gear, without deploying the ship's Prince William Sound Towing Package.
Drills were also used to assess crew skills in towing large tankers in
adverse weather with multiple tugs. He concludes that additional drills
and training, both in the makeup and towing operations, would be
beneficial.
Captain ter Haar concludes that the vessels presently under
contract are suitable for rescue towing in Prince William Sound under a
full range of weather conditions. In the open waters of the Gulf of
Alaska, at and beyond Hinchinbrook Entrance, he concludes that a larger
salvage tug would improve the capability to prevent a major casualty.
Summary of Part 2
Part 2 of the DTTS, is entitled ``Computer Simulations of Escort
and Rescue Towing Scenarios.'' Part 2 evaluates, using computer
simulations, the capability of existing escort vessels in Prince
William Sound, Alaska, and examines alternatives, if any, that could
enhance escort and rescue towing capabilities in a worst case failure
scenario. The study was subsequently expanded to include a parametric
study to investigate the consequences of variants from the worst case.
The parametric variables included wind speed, tanker speed, failure
rudder angle, failure recognition time and tug notification time.
Tug escort of laden tankers has been a feature of tanker operations
in Valdez Narrows since the opening of Alyeska Valdez Marine Terminal
in 1977. Shortly after the grounding of the EXXON VALDEZ in 1989,
escorting was extended all the way through Prince William Sound to Seal
Rocks in the Gulf of Alaska.
Tankers calling in Prince William Sound range in size from 60,000
to 265,000 DWT. Three representative sizes, 90,000 DWT, 170,000 DWT and
265,000 DWT, were chosen for computer simulation.
In developing the parameters of the study, it was decided that
worst-case scenarios would be investigated because if the escort system
was effective in worst cases it would be effective in all situations.
The worst-case scenario was a combination of: a hard-over rudder
failure, loss of power, extreme weather conditions, a failure
recognition delay and a conservative definition of areas (red zones)
where a response effort would be considered ineffective.
The study investigated (via computer simulations) five geographic
locations in Prince William Sound (PWS): Valdez Narrows; Valdez Arm;
central Prince William Sound; Hinchinbrook Entrance; and the Gulf of
Alaska near Seal Rocks. The climatology used for this study was the
worst-case wind and sea state resulting from a 25-year return period
storm or the defined closure condition in each of the study's
geographic areas.
The study defined the worst-case tanker failure scenario to be:
--A 35-degree locked rudder failure.
--A time delay for failure recognition.
--Simultaneous shutdown or loss of the propulsion system upon rudder
failure recognition.
The parametric study investigated less extreme variations to the
failure scenario (rudder failures at 10 and 20 degrees, shorter time
delays for failure recognition and tug notification, and reversing of
the tanker engine).
Each class of tugs currently on charter was modeled for use in the
computer simulations, as well as four other tug designs as possible
alternatives. These alternative vessels were:
--4000 BHP vertical axis propeller tractor tug.
--7600 BHP vertical axis propeller tractor tug.
--7110 BHP azimuthing propeller (Z-drive) pusher tug (sometimes called
a reverse tractor).
--168-ton bollard pull deep sea salvage tug.
1 [[Page 6347]] The ability of the various types and sizes of tugs
to perform escort and emergency towing was determined based on existing
performance data, computer simulations and available operating
experience.
A matrix of simulation cases was developed, representing a full
range of combinations of tug types, deployments and associated time
delays, geographic locations and tanker sizes and speeds. In addition
to the matrix of worst-case scenarios, over 1,000 additional cases,
involving parametric reductions in the severity of the defined
variables, were performed.
The study's results of the worst-case and parametric studies are
summarized below.
--For the worst-case scenario, the larger tractor tug (with additional
assist from an untethered ERV tug), or the largest conventional tug
tethered as a rudder tug (with additional assist from another
conventional tug and an ERV tug both tethered alongside), is capable of
controlling all three modeled tankers in the Valdez Narrows if the
tanker speed at failure is less than or equal 4 knots.
--All of the current escort tugs have adequate power to tow a disabled
tanker in the worst-case climatology of Valdez Arm. However, the
simulations show the need for increasing the sea room between the
outbound track and Buoy 9 near Pt. Freemantle.
--Both the SEA VOYAGER and the ERV class tugs are capable of towing any
of the three sizes of tankers to windward in the modeled worst-case
(45-knot wind) conditions for central Prince William Sound. However,
there is inadequate sea room from the TSS lane to Naked Island for the
tug to rig its towline and begin towing. In lesser wind speed
conditions, however, there would be adequate sea room for these tugs to
begin towing before any of the three sizes of tankers reached Naked
Island. A SEA SWIFT class tug requires additional assistance from an
ERV tug to tow any of the three sizes of tankers to windward.
--There is insufficient sea room to accommodate arrival time delays of
existing tugs on standby at the Pilot Station, Naked Island or Port
Etches based on the worst-case parameters set for this study. This
result supports the current escort policy in Prince William Sound.
--The simulations for Hinchinbrook Entrance in the worst-case
climatology show the need for increasing the sea room between the
outbound track and Montague Island. For all cases with a right rudder
failure occurring in the center of the southbound separation lane, the
tanker will enter the red zone around Schooner Rock before an escorting
tug can provide effective assistance.
--However, the parametric study for Hinchinbrook Entrance identifies
some successful combinations under reduced wind conditions that result
in towing control before the disabled vessel enters the red zone.
--None of the tugs investigated in this study can tow the modeled
170,000 and 265,000 DWT vessels to windward in the worst-case
climatology identified for the Gulf of Alaska. However, both the
simulated SEA VOYAGER class tug and the salvage tug at least have the
capability to control its downwind drift direction.
--The simulations indicate that the salvage tug can tow the disabled
90,000 DWT vessel to windward in the Gulf of Alaska given the assumed
worst-case conditions.
--The parametric study of reduced wind conditions for the Gulf of
Alaska show that all three sizes of tankers can be towed to windward by
the SEA VOYAGER class tug in 30 knots of wind or less or by the salvage
tug in 50 knots of wind or less.
Dated: January 24, 1995.
Joseph J. Angelo,
Acting Chief, Office of Marine Safety, Security and Environmental
Protection.
[FR Doc. 95-2493 Filed 1-31-95; 8:45 am]
BILLING CODE 4910-14-P
