One recurring comment related to the collision between the USS Fitzgerald and the container ship ACX Crystal was that the container ship might not have been able to see the destroyer over the containers stacked on deck. There are photographs of containers on ACX Crystal stacked five high on deck forward of the house. Exactly how far forward did the ship’s blind spot extend? Was the view of of the USS Fitzgerald obscured by the containers stowed on the 2,858 TEU container ship? Are standards for container ship visibility too lax?
No doubt the answers to these questions will be answered in the multiple ongoing investigations. The answers will depend on the specifics of the container stow plan on the ACX Crystal as well as the ship’s draft and trim.
Visibility, however, may only be part of the story. Maneuverability — the ability to stop and/or turn the ship — can be even more important.
If we do not know exactly what the visibility was on the ACX Crystal prior to the collision, we do know what it should have been. The SOLAS (Safety of Life at Sea Convention) Regulation 22 defines the minimum visibility allowed.
Specifically, “the view of the sea surface from the conning position shall not be obscured by more than two ship lengths, or 500 m, whichever is the less, forward of the bow to 10 deg; on either side under all conditions of draught, trim and deck cargo…” The visibility requirement in the Panama Canal is slightly tougher at 1.5 ship lengths.
In the case of the ACX Crystal, the SOLAS allowable blind spot is about 445 meters (1,461′) or just under a quarter nautical mile.
But, if the rules for visibility are two ship lengths, the realities of ship mass ad velocity make job of turning or stopping the ship even more challenging. At design speed, container ships are usually more constrained their ability to maneuver than by visibility.
For example, the international standard for container ships making a crash stop from design speed is 15 ship lengths, or over 7 times the allowable blind spot.
Ships generally can avoid a collision more effectively by turning rather than stopping. The minimum allowed turning radius is 5 ship lengths. The advance, the forward distance traveled in making the turn, is 4.5 ship lengths, still more than twice the allowed blind spot.
What all this means is that if the master on the bridge of a container ship waits to respond to a potential collision until the other vessel is close to his blindspot, there may not be enough time to maneuver the ship to avoid a collision.
Maneuverability is a function of a ship’s speed and the rules are all based on designed speeds. At lower speeds, particularity when traveling slowly in a harbor, visibility may a play a much larger role.
So, until the investigators finish their work we will not know the facts of the Fitzgerald/Crystal collision. Nevertheless, all else being equal, it appears that visibility from the bridge of the container ship is not likely to be a primary cause of the collision.
Thanks to Robin Denny for contributing to this post.