The Prince William Sound tanker escort system has a complex structure that provides extra security through the most dangerous areas of the Sound. Three “escort zones”, Northern Prince William Sound, Central Prince William Sound, and the Hinchinbrook Entrance have varying escort requirements.
Within the Sound, tankers are subject to various speed limits. The highest speed limit applies in central Prince William Sound. The lowest applies in Valdez Narrows. Laden tankers may not exceed a speed beyond which the escort vessels can reasonably be expected to safely bring the tanker under control.
Laden tanker speed limits in Prince William Sound
Port Valdez: 10 knots
Valdez Narrows: 6 knots
Valdez Arm: 10 knots
Buoy #9: 8 knots
During Ice Escort: safe speed
Central Sound: 12 knots
Hinchinbrook Entrance: 10 knots
Northern Prince William Sound
Through the Valdez Narrows, one of the escorts must be tethered to the tanker’s stern. At the north end of the Sound (from the Valdez Marine Terminal to the Bligh Reef light) and at the south end, where tankers enter the Gulf of Alaska via Hinchinbrook Entrance, all escorts must stay within a quarter nautical mile of the tanker.
Central Prince William Sound
In the central part of the sound (from the Bligh Reef light to the Hinchinbrook Entrance) there is more sea room and only one of the escorts is required to stay within a quarter nautical mile of the tanker. The other escort (called a “Sentinel”) may be stationed a few miles away at one of three points along the route, close enough to be able to provide a quick response.
Hinchinbrook Entrance
Two close escorts are required through Hinchinbrook Entrance. After a tanker leaves Prince William Sound, a rescue tug must stay on station near Hinchinbrook Entrance until the tanker is at least 17 miles out to sea.