Study shows purpose-driven design can improve performance

When a ship is disabled at sea, an appropriate rescue vessel must respond quickly to prevent an accident. Towing can be dangerous, especially in rough weather, because the rescue tug must get close to connect a towline.

Challenging environment in Alaska

Map showing the tanker traffic lane. The tankers must pass through a relatively narrow area between Hinchinbrook and Montague Islands when entering or leaving Prince William Sound to or from the Gulf of Alaska. A rescue tug with the right features has the best chance of preventing a spill.
Alaska requires a tug stationed in the vicinity of Hinchinbrook Entrance, the narrow waterway which connects Prince William Sound to the Gulf of Alaska. The tug remains on standby to assist or escort tankers through the entrance and out into the Gulf of Alaska.

Hinchinbrook Entrance is a narrow waterway that connects Prince William Sound to the Gulf of Alaska. The weather and sailing conditions in the gulf can change rapidly and are often severe.

Tankers carrying millions of gallons of oil regularly pass through the Entrance. Alyeska’s Ship Escort/Response Vessel System must have a tug stationed at the Entrance when laden tankers travel through Prince William Sound.

What is the right tug for this role?

The Council recently asked the experts at Glosten, naval architecture and marine engineering firm, to help answer this question.

Glosten began by reviewing designs and technologies for existing tugs. They summarized the ideal tug design, describing the dimensions, power, propulsor (propeller) types, shape, ability to withstand rough seas, machinery, and towing gear, among other features and equipment.

Glosten then compiled a database of around 4,000 tugs in use around the world. Using the ideal summary as a guide, they narrowed the list to tugs:

  • Built in 2005 or later
  • Between 130 and 260 feet long
  • Able to exert between 130 and 200 tons of pulling or towing power
  • Capable of speeds of 18 miles per hour
  • Within a reasonable cost to design, build, and operate

Fewer than 400 were left.

Tasks the tug must perform

Glosten then outlined the demands placed on the Hinchinbrook tug at each stage of response. Based on these demands, Glosten concluded a state-of-the-art design for the Hinchinbrook tug must provide exceptional performance in three categories. The ideal tug must be able to maintain these in a broad range of sea states:

  • A high free-running speed
  • A high degree of maneuverability and agility
  • High bollard pull (towing ability) and towing efficiency

After ranking the 400 tugs according to all these features and abilities, they were down to the 17 top scoring tugs.

Finding the right balance

After balancing performance with costs, Glosten determined that the existing vessel most closely matching the needs for an ideal Hinchinbrook tug was the Luz de Mar: a tug operated by Spain’s Maritime Safety and Rescue Society.

The creators of the Luz de Mar designed it for offshore ship rescue and response. This means the Luz de Mar is maneuverable and agile due to a powerful propulsion system, has adequate bollard pull, can aid a disabled tanker in a variety of ways, and is still fast enough for a quick response.

How does the current tug compare?

Glosten studied the differences between the Luz de Mar and the current tug serving Hinchinbrook Entrance, the Ross Chouest.

Their study showed that a tug designed specifically for that role would improve safety and efficiency, improve response times, and reduce the chance of an oil spill.

Conclusion: Purpose-built tugs work better

The researchers noted that many believe the largest and most powerful tugs are ideal for rescue operations. In fact, the design of these larger vessels does not prioritize the features most important to a successful emergency response.

They concluded that a tug designed with this purpose in mind offers significant advantages, especially when a rescue tug works close to shore.

More details

A recent issue of International Tug and Salvage has a more detailed article by Peter Soles of Glosten and Alan Sorum of the Council, available on the magazine’s website: Defining the best technology for emergency rescue tugs

Glosten’s full report:

Hinchinbrook Emergency Towing Vessel (ETV) Best Available Technology (BAT) Assessment (20.4 MB)

NEW VIDEO! Study of line-throwing technology demonstrates importance of the Council’s independent research

Photo shows Coast Guard officer firing a messenger shot line from one Coast Guard vessel to another. This is one method of connecting tow lines between a tug and a tanker.
In this 2016 photo, a U.S. Coast Guard officer fires a messenger line from one military vessel to another. This is one method of connecting tow lines between a tug and a tanker. Photo by Pasquale Sena, U.S. Coast Guard.

A new study evaluating methods of establishing tow lines between an escort tug and a tanker in distress is a prime example of why the Council’s studies are vital.

The Council often hires experts to review equipment technology used in the Prince William Sound oil transportation industry. Sometimes these studies fill a hole or gap where independent research is lacking.

“Very little has been previously written on this topic,” said Alan Sorum, who managed this project and other similar technology reviews for the Council. “In a literature review it conducted, the Council’s contractor, Glosten, found that there is a general lack of published material on this subject and in particular, little guidance on best use practices or what is the most appropriate device to use for a given situation.”

Watch the new video released in 2022

The study looked at a specific piece of equipment called a “messenger line.” Passing a messenger line is the first step in setting up a tow line between a tug and a tanker in distress. The lighter weight messenger line helps responders connect the heavy tow lines.

Retrieving a messenger line can be difficult and dangerous in the rough weather often encountered in Prince William Sound. Depending on the vessel and the technology on board, they may be passed by hand, heaved or thrown aboard, projected by mechanical means, or picked out of the water.

Tough equipment required for Alaska’s harsh climate

Alaska has a state law that requires tankers to carry specially designed towing equipment when traveling through Prince William Sound. This equipment includes a towing wire, floating line and buoy, and a heavy-duty shackle.

These components are all specifically sized to match the weight of the vessel and be able to handle the high winds and seas often encountered in Prince William Sound.

Having this specialized equipment on hand allows rescue tugs to quickly and safely help move a stricken tanker to a safer location.

Conducting the study

Researchers reviewed what devices are commercially available for deploying messenger lines. Next, they developed criteria to evaluate the equipment according to: effectiveness, feasibility, transferability, compatibility, age and condition, availability, environmental impacts, and cost.

These eight criteria were based on another Alaska law, which requires industry to use “best available technology.” This requirement is intended to ensure that equipment meets and is maintained to a high standard.

The equipment options were each assessed and scored.

How will the Council use this information on tow lines?

The Council’s influence depends on quality, accurate research. The Council uses reports like this to help make sure advice given to industry and government officials is well-informed and supported by the best science available. The findings of this latest research effort are being shared with equipment manufacturers, the oil transportation and shipping industries, and regulators.

Read more about the researcher’s recommendations:

Tanker Towline Deployment BAT Review (10.3 MB)

New video demos lessons learned during on-water tests

The Council joined Glosten and others in Puget Sound in 2021 to test the results of this study. 

Trouble viewing the video? View directly on our Youtube channel.

Full report on 2021 trials:

PWSRCAC Emergency Towline Deployment Practical Trial Summary Report (1.7 MB)


Oil spill prevention and response services transition to new contractor

Link to more photos of new equipment
More photos of new equipment.

Prince William Sound was a hive of activity this summer. On July 1, Alyeska’s marine services contractor transitioned from Crowley Maritime Corporation to Edison Chouest Offshore.

This transition means all of the escort tugs and much of the spill prevention and response equipment in Prince William Sound are brand new, or new to the Sound.

Demonstrations of the new equipment

The Alaska Department of Environmental Conservation required that each vessel and crew member demonstrate their capabilities before beginning service. Each tug, as well as each tug’s captain, had to perform a set of maneuvers which differed according to the vessel and its purpose.

Read more

Changes to oil spill contingency plans approved

Extensive amendments due to transition

Photo of oil spill contingency plans with the caption: What is a contingency plan? A contingency plan, or “c-plan,” outlines steps to be taken before, during, and after an emergency. An oil spill contingency plan contains detailed information on how to prevent an oil spill, as well as response activities in the event a spill occurs. Preventing an oil spill from occurring in the first place is the most effective way to protect human health and the environment. If an oil spill occurs, however, a systematic and well-organized approach is necessary to quickly contain and control a spill. Responding efficiently and effectively to a spill requires advanced planning and preparedness.
What is a contingency plan?

The Alaska Department of Environmental Conservation recently approved major amendments to oil spill contingency plans for both the Valdez Marine Terminal and for the tankers that transport oil through Prince William Sound. Both approvals came with conditions.

Neither the tanker plan, nor the terminal plan was due for a renewal. However, Edison Chouest Offshore is bringing so much new equipment and personnel to their new role as Alyeska’s marine services contractor that major changes were needed to both plans. Major amendments require a public comment period.

Read more

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