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Among other things, the boats’ metal frame and heavy chassis and transmission combined with the lack of reserve buoyancy means they sink quickly, and their low freeboard means passengers have little time to escape in an emergency.

Their metal frame and heavy chassis and transmission combined with the lack of reserve buoyancy mean they sink quickly.

We also reported then that the boats needed “reserve buoyancy,” such as foam or bulkheads, to help them stay afloat in adverse conditions.

The N.T.S.B. said it had pushed for the Coast Guard to require duck boats to have more watertight spaces above the waterline, known as reserve buoyancy, and to remove obstructions such as overhead canopies that could hamper an evacuation.

The recommendations included removing overhead canopies that could trap passengers as the boat sank and implementing a reserve buoyancy mechanism to keep the boats from sinking at all.