How Boat and Ship Collisions Are Reconstructed

Every collision case starts with two stories, and they rarely match. One watch officer swears the other vessel turned into him. The other swears he held his course. Both may believe it. Memory under stress is a poor instrument.

Reconstruction is how you get past the stories. It is slow, detailed work, and it follows the same basic order every time.

Step one: collect every source of time and position

Modern vessels leave a trail. The main sources are:

• AIS (Automatic Identification System): position, course, speed, and heading broadcast by most commercial vessels, received by shore stations, satellites, and other ships.
• The voyage data recorder on vessels required to carry one: bridge audio, radar images, positions, engine and rudder orders, and more.
• Radar and ECDIS records, where the equipment saved them.
• VHF recordings, from the vessels, the Coast Guard, or a vessel traffic service.
• Logs: deck log, bell book, engine data.
• Witness statements, taken as early as possible.

None of these is perfect. AIS reports come at intervals that vary with speed and can drop out in busy areas. Time stamps differ between systems. A ship's AIS antenna is rarely at the bridge, so the reported position is not quite where the conning officer was standing. Part of the expert's job is reconciling these sources rather than picking the one that helps.

Step two: build a single timeline

I line every source up on one clock and build a timeline, usually minute by minute in the final approach and second by second in the last few minutes. Then I plot it. A chart showing both vessels' tracks, with time marks, does more for a jury than an hour of testimony.

The timeline shows when each vessel could first have seen the other, when risk of collision existed, when each one acted, and how much those actions changed things.

Step three: identify the situation under the rules

The rules of the road divide encounters into situations, and each carries its own duties.

• Head-on (Rule 14): both vessels alter to starboard.
• Crossing (Rule 15): the vessel with the other on her starboard side keeps out of the way.
• Overtaking (Rule 13): the overtaking vessel keeps clear, for as long as she is overtaking.

On top of those sit duties that apply to everyone. A proper lookout by sight and hearing and all available means (Rule 5). A safe speed for the conditions (Rule 6). Using every available means to decide whether risk of collision exists (Rule 7). Action to avoid collision that is taken early, is large enough to be obvious, and is made with good seamanship (Rule 8). In restricted visibility, Rule 19 changes the picture again.

Getting the situation right matters. Many cases turn on whether it was a crossing or an overtaking, because that decides who had the duty to keep clear.

Step four: measure each vessel against the standard

With the timeline and the rules in hand, the question becomes concrete. At this minute, what did a prudent mariner on this vessel know, or have the means to know? What should he have done? What did he do?

That analysis covers more than rudder and engine orders. It covers who was on the bridge, whether the lookout was actually looking, whether the radar was set up for the range that mattered, whether the vessels talked on the radio and whether that conversation helped or confused things.

Step five: deal with both vessels honestly

Admiralty courts allocate fault by percentage. Since United States v. Reliable Transfer Co. (1975), damages are divided according to each party's degree of fault rather than split down the middle. That means the expert has to look at both vessels, not just the one he was hired to criticize. An opinion that finds the other side 100 percent at fault, when the record shows mistakes on both bridges, will not survive cross-examination.

Where the human factors come in

The tracks show what happened. They do not show why. Fatigue, distraction, a bridge team that did not speak up, an officer who misread a radar picture, a pilot and master who never agreed on the plan. Those are the questions that usually explain a collision, and they come from logs, training records, rest-hour records, and testimony, not from AIS.

A note on my background

I navigated tankers through open ocean and some of the busiest harbors in the country, and I served on the Navigation Safety Advisory Council, which advises the Coast Guard on the rules of the road. When I reconstruct a collision, I am asking what I would have expected of an officer on my own bridge.

About the author

Captain Mitchell S. Stoller is a Master Mariner Unlimited, former Exxon tanker master, and former Los Angeles Harbor pilot. About Captain Stoller