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Alaska escort contract resurrects debate over winch safety

Aug 26, 2015 11:28 AM
Nanuq is a cycloidal-drive enhanced tractor tug that has served in the Prince William Sound escort fleet under the existing contract.

Courtesy Citizens’ Advisory Council

Nanuq is a cycloidal-drive enhanced tractor tug that has served in the Prince William Sound escort fleet under the existing contract.

The renewal of the contract for tugboats and recovery barges in the escort and oil-recovery program in Alaska’s Prince William Sound is seen as a chance to bring in the best available technology for towing winches, a concern of a local citizens group.

Alyeska Pipeline Service Co. issued a request for proposal (RFP) for the tugs and barges that make up the Ship Escort/Response Vessel System (SERVS), according to Mark Swanson, executive director of the Prince William Sound Regional Citizens’ Advisory Council. He said the RFP is for 11 escort and response tugs and nine oil recovery barges. The deadline for proposals was May, according to Kate Dugan, spokeswoman for Alyeska.

“Our understanding is it is a 15-year deal,” Swanson said.

Dugan said the contract starts in 2018. Alyeska Pipeline would not release further details of the proposal.

The SERVS system was created in 1989 to prevent oil spills and create an oil-response and preparedness system in the wake of the Exxon Valdez disaster.

Federal law requires that every fuel tanker traveling through Prince William Sound must be escorted by two tugs. The primary escort tugs are two enhanced tractor tugs (ETT) and three prevention and response tugs (PRT), built in 1998 and operated by Crowley Maritime. The ETT tugs are cycloidal drive; the PRT tugs are azimuthing drive. The other six are twin-screw conventional tugs.

“This relet of the Prince William Sound contract is an ideal opportunity to make sure these vessels are fit for purpose,” said Swanson. “We really think this is an opportunity to move forward. We’ve been badgering away at this. We’re not sure we’re going to get it.”

The advisory council commissioned a study by naval architect Robert Allan to determine whether the SERVS escort tugs were using the best technology available in tug design. Allan’s study, dated August 2012, found that the winches used by the escort tugs were not state-of-the-art and should be replaced. (See story, PM 166, March 2013).

“The SERVS tugs are well-equipped vessels,” Allan wrote in the study. “The towing systems, however, fail to reach today’s BAT (best available technology) definition primarily in the type of escort winches used, as that technology has changed dramatically in the past decade.”

Allan wrote that the lack of a render-recover type winch on the ETT-class vessels “is considered a fairly significant deficiency in comparison to escort-rated tugs being built in say the past five years.”

Allan in July 2015 would not comment on the new RFP.
 

Attentive is an azimuthing stern drive tug at work in the sound. A new escort contract is being negotiated, and an earlier research report called for updated winch technology on the Alaska boats.

Courtesy Citizens’ Advisory Council

Andres Morales, director of Alyeska’s SERVS, told Professional Mariner in 2013 that the current winches are up to the job and were overbuilt for what was needed. They were designed for a much higher standard than normal for the industry, he said.

Swanson said the main concern is with the escort tugs’ winches. “We would specifically like to see render-recover winches of the type that are engineered to meet any escort notation for any of the International Association of Classification Societies that have a robust escort notation,” he said.

The SERVS tugs meet the American Bureau of Shipping (ABS) class requirements for escort tugs.

“However, the trend in the industry worldwide is to look at the higher DNV (Det Norske Veritas) escort notation,” Allan wrote in the 2012 study. ABS allegedly did not have the highest standards in the industry for escort tugs at the time of the study. Since the study, DNV has become DNV GL.

Swanson would like the new contract to make sure that the escort tugs meet proper stability requirements for indirect towing, which is when the tugs go out into a position where the towline is at a 90-degree angle from the centerline.

Allan wrote that ABS requirements for an escort-class notation only require that maximum forces do not immerse the deck edge of a tug. DNV and other class societies have requirements that define the required ratio of righting movement to heeling movement that includes some margin of freeboard, according to Allan’s report.

Analyzing stability criteria is difficult because of lack of information, Swanson said.

“A major gap in the data is the absence of a known indirect steering force capability of the tugs,” wrote Allan, who advised that this should be quantified.

SERVS needs to meet state requirements, according to John Kotula, marine vessels section manager for the Alaska Department of Environmental Conservation’s Division of Spill Prevention and Response.

“Under state law, they have to be able to provide the intended service,” he said. “They have to do everything that needs to be done — take a disabled tanker and save it from the rocks and take it under tow.”

Kotula said the state would evaluate the performance of the new tugs through exercises to prove they can provide the intended service. “For us, it’s an end-of-the-line situation,” he said. “When (Alyeska) gets whatever the RFP brings them, it’s got to meet all the regulatory requirements.”

“We have been satisfied with the escort tugs. They have always been able to provide the required service,” Kotula said. “That’s not to say that, as technology improves, there are going to be ways to make improvements.”

Sep 22, 2015 12:51 am
 Posted by  bjdme

After reading your article on the Alaska escort debate over winch safety and knowing Robert Allan to be the leading authority in tug escorting, I was surprised to see the article key on the winches' lack of a constant tension (CT) system. As noted in a response to an article in PM 166 March 2013, these hydraulic winches can be backfit to accommodate this type of function. During the escort mode, also known as the emergency steering mode, the winch needs to be locked down so it will not pay out when the forces are needed to turn the tanker. DNV requires that the winch recover at the indirect bollard pull when in fact if the winch renders and is controlled by a scope limit system, then it is negated. A better solution would be to a have a double-drum winch with two lines up to the tanker. The design of a proper escort system involves the tug's performance, the winch to match that performance, foundation and brake, the tug's staple, the towline and the bitt on the tanker. If one of the components is missing, the system is in question. A CT system may be a nice option to have when tethered to the tanker or to freewheel away from its tow, but when in the indirect mode — when you are directed by the pilot to change speeds, fly from one side of the tanker to the other, the rope dives or you hit a constant scope limit — the CT system needs to be adjusted. During an emergency operation you have little time to think and only two hands to operate the tug, and the time to respond may be seconds for success or failure. The DNV rule, although well intended, is misunderstood by the industry. As stated, you are in an emergency mode with little time to adjust winch settings to accommodate a pilot's commands when the tug is jackknifed behind a tanker.

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