Maritime Operations

New study analyzes weather at Hinchinbrook Entrance

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A recent Council-sponsored report found that wind and waves at Hinchinbrook Entrance may be under reported as observed by the Seal Rocks weather buoy.

Researchers from Tetra Tech analyzed wind and wave data to better define weather conditions at the Entrance, as well as how these conditions might affect rescue operations by the escort tugs. To do this, researchers looked at the frequency and duration of weather events when the Entrance was closed to laden tankers.

Average closure conditions

A "wind rose" graphic that shows the speed and direction of wind as recorded at Seal Rocks.
This “wind rose” graphic shows the speed and direction of wind as recorded at Seal Rocks.

Wave height alone was found to be the cause of most of the closures, occurring 10 to 26 times a year on average. Average wave height during closures was over 17 feet and the highest recorded wave was over 26 feet. Wind speed closes the Entrance one to three times annually, as do closures for both wind and waves. Winds average just over 54 miles per hour during closure and the highest recorded wind speed was over 61 miles per hour.

Closures for winds typically last less than two hours, while waves close the Entrance for an average of just over six hours.

Seal Rocks buoy’s data may not be precise

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Out-of-service buoy and winter storms raise concerns

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An out-of-service buoy and a series of recent storms have combined to raise concern at the Council about tanker transit procedures during period with the high wind speeds and wave heights in which tankers are allowed to travel through Prince William Sound.

Seal Rocks buoy out of service


From May until December of 2018, a critical buoy located near Hinchinbrook Entrance was out-of-service. This buoy, referred to as “Seal Rocks buoy,” collects wind speed and wave height data. That information is used by the U.S. Coast Guard to make decisions as to whether Hinchinbrook Entrance is open or closed to outbound laden oil tanker traffic. When this buoy is inoperable, the U.S. Coast Guard uses data from two nearby buoys, Cape Cleare and Cape Suckling, along with reports from Edison Chouest Offshore, or ECO, tug crews that are sent out to observe wind and waves to make Hinchinbrook Entrance open and closure decisions.

In November and December, several winter storms came through Prince William Sound that raised concern about these alternate methods for reporting weather conditions at the Entrance.

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Oil spill prevention and response services transition to new contractor

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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.

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Changes to oil spill contingency plans approved

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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.

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