I have very little experience in relation to Ken's wide knowledge, but I would say that if the boat was being run on diesels in very heavy seas with the air intake valves open and the heave seas "swamped" the air intakes with sea water (from large waves), then the intake manifolds (and associated superchargers, etc.) would fill with sea water and probably "hydrolock" the pistons in the cylinders. This mechanical failure would bend connecting rods, bend or break crankshafts, break pistons, damage cylinder heads and/or valve gear, etc.

Yes, this would result in total wreckage of the diesel engines. You would not want to run, or try to start, diesel engines if water is pouring into the intakes.

But that's just my guess. I welcome any other discussions.