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Questions over new Valdez fleet
With construction underway of a new fleet of tugs to support oil tanker operations at the Valdez Marine Terminal and in Prince William Sound, a new report commissioned by the Prince William Sound Regional Citizens’ Advisory Council has questioned whether the tug designs adequately cater to the demanding operating conditions at the terminal and in the sound. A draft version of the report, by naval architects and marine engineers Robert Allan Ltd., says that the tug designs require more thorough evaluation, especially with respect to operating conditions in Alaska sea and climate conditions. Alyeska Pipeline Service Co., the operator of the marine terminal and the trans-Alaska oil pipeline, says it is reviewing the draft report, which has only just been released, and that it is confident that the new fleet will maintain services at current performance levels.
The fleet change comes as part of a transition from Crowley Maritime Corp. to Edison Chouest Offshore for the provision of vessel services for the Valdez terminal. Edison Chouest is contracted to take over the marine services in July 2018. The services include the provision of tug assistance for tankers docking at the terminal, and the support of oil spill prevention and response arrangements for the terminal and for the tanker operations across Prince William Sound and Port Valdez.
New tug fleet To replace Crowley’s existing tug fleet, Edison Chouest is building five new tugs for escorting oil tankers and four general purpose tugs. Construction of the new tugs has already started, with sea trials of the new escort tugs expected to begin in December 2017.
Concerned to ensure that Edison Chouest’s services meet the demanding requirements for operating in the harsh marine environment of the Valdez area, the PWSRCAC commissioned Robert Allan Ltd. to review specifications and drawings for the tugs and to comment on the suitability of the designs for the required marine services.
During a PWSRCAC board meeting on Jan. 19 Robert Allan, the company’s executive chairman, reviewed his company’s report’s contents. Edison Chouest is building the tugs using designs developed by Damen, a major international shipbuilder. Allan commented that, although his company and Damen are business competitors, the report findings result from an objective evaluation by professional engineers with knowledge of the operating conditions involved in the required marine services.
Powerful tugs The new tanker escort tugs have higher power ratings than the Crowley tugs that they will replace. Allan said that, although Damen is a company with substantial experience of designing and building tugs, these new tugs are larger than any tug that the company has previously designed. But, with a power rating of 12,336 horsepower, the new tugs will be fully powerful enough for the required operations, Allan said.
However, Allan questioned the pulling performance quoted both for the new escort tugs and for the new general purpose tugs, saying that the performance seems low in relation to the tugs’ power. A too-low performance rating runs the risk of the tug overpowering the towing equipment and impacting the stability of the boat, he warned, saying that he would like to see an explanation of how the performance rating was calculated.
Allan also questioned the apparent lack of scale model testing of the escort tug design, an omission that he viewed as very serious, given the demanding nature of the tugs’ required operations. Those operations include the tethered escorting of tankers through the Valdez Narrows; tanker escorting across the eastern end of Prince William Sound; emergency towing; and oil spill response support. Moreover, Allan said, computer modeling of the escort tug performance seemed simplistic and did not appear to have taken account of the full speed at which the tugs would be required to operate, and of the more severe sea states that can occur in Prince William Sound and the Gulf of Alaska.
Design questions In terms of the tug design, Allan questioned the high deck housing, a structure that would be impacted by strong winds, and the very large size of the “skeg,” the keel-like structure that runs the length of the vessel’s underside. Given these factors, a bow thruster would significantly improve vessel handling at slow speeds, he suggested. The vessels appear to have insufficient fendering for Prince William Sound operations, and the bow shape and height appeared inappropriate for rough sea conditions in the Gulf of Alaska. Moreover, the design of the deck towards the front of the ship seemed likely to result in the pooling of water in heavy seas, Allan commented.
Allan also said that the design of the accommodations inside both the escort and general purpose tugs appeared unsuitable for operations in the Alaska winter, with, for example, bunks placed adjacent the hull, where temperatures would be coldest and the motion of the ship would be most severe. He also commented that no information had been provided on other aspects of ship design appropriate to Alaska operations, such as the protection and heating of mooring lines, the heating of decks in exposed working areas, and the need to protect winches from freezing spray.
Allan cautioned that fixing any design issues with the new vessels would be much cheaper at the design stage than following construction.
Tug capabilities With respect to the general purpose tugs, Allan questioned the apparent lack of evidence that these tugs will have the capability to provide tethered escorting of smaller tankers, one of the tasks that the smaller tugs were listed as required to be able to conduct. He also questioned whether these tugs would be fast enough to provide untethered escort services for tankers. And, in the interests of ensuring that the tug engines do not stall when maneuvering a vessel, he recommended the use of variable pitch propellers, rather than the fixed pitch propellers that the design assumes.
Alyeska reviewing report Andres Morales from Alyeska SERVS told the PWSRCAC board that his company is taking the information in the Robert Allan report to heart and has reached out to Edison Chouest for answers to the questions raised. SERVS has only just received the report and anticipates providing feedback in due course, Morales said.
Morales said that the performance requirements for the new vessels are specified in the oil spill prevention and response contingency plans for the tanker operations. Morales also commented that the general purpose tugs would be fully tested for use in escort duties, should it be decided at some point that these tugs would be used for that purpose. And Graham Wood from the Alaska Department of Environmental Conservation said that the state’s expectation is that, following the transition to Edison Chouest, there will be no net loss of performance relative to the current arrangements in place for the protection of Prince William Sound.
Donna Schantz, executive director of the PWSRCAC, requested that missing information that has generated many of the concerns expressed in the Robert Allan report be made available.
- ALAN BAILEY
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