Is it possible to hydrolock running engine?

[skenn_ie]

IMO, only if it sucks fluid in through the air intake. That is quite common with people trying to drive through flooded roads. Some vehicles, even 4x4s, have the air intake below the radiator !
The other sudden stop is a broken camchain or belt, but I suspect that you engine doesn't have an overhead camshaft.

[oceansailor203]

Does it have a decompression lever?

[Kurlie1]

I had a saildrive bearing failure due to a damaged seal (motored through stray comercial fishing junk) The resulting seisure bent the pinion and jolted the sail drive casing to such an extent that the main seal was damaged and the boat began to sink. Luckily it was a slow leak and I was able to pump enough to keep afloat as I sailed to port (only 40nm) until I docked and hauled. The whole unit needed replacing as it was full of redundant parts .... ended up in a full repower!

[Wolfgang.Schau]

I had the same problem with one of my Volvo D1-30 (I have two on my catamaran).
There was charcoal buildup the mixing elbow after the manifold. The result was that sea water always was standing there and eventually rusting through. At the end, it rusted through it and sea water could get back into the cylinder head. If water gets backwards into the cylinder, it brings it to an immediate stop because water cannot be compressed. I did not hear a big bang as others mentioned.
This engine was 6 years old by then.
As remedy, I ordered a new mixing elbow (stainless steel this time), took the cylinder head off, cleaned everything and put it back together. It runs now for another 5 years. Soon I will check the elbows to see if there is another issue looming.

Other sailors have invented a way to flush the sea water cooling loop with fresh water before the engine is shut off. This may reduce the impact of saltwater standing there. However, if freshwater is standing there, it'll still rust, but more slowly.

A Volvo technician told me an important thing: Before you turn your engine off, run it at full power for some time, this will burn away the charcoal sediments in the exhaust system. At the end of every trip, I run the engine at max rpm for 10min, maybe it helps.

[skipperguy]

Yes! Happened to me in the 1980s. MerCruiser 188 engine. Replaced manifolds and risers with Osco center exit and never had the problem again

[RaymondR]

I'd say that as a general rule, if the water inside the boat gets high enough to flood the intake engine hydrolocking the engine might be one of your lesser problems.