Water in Engine ??
I am a new owner of a 1993 Maxum 2700 SCR which had similar problems of water in the engine, there were several problems with my engine, here is a list of what you might check..bizzarly enough, my engine was running perfectly and only noticed the water when checking the oil....I would caution you to look farther than internal engine component failure, There are several components on the engine that can corrode to the point of actual holes in the exterior casing that will allow water into the engine, including as far as freeze plugs
1) Exhaust manifolds (to really check, they must be pressure tested)
2) any holes in the oil pump/cooler case
3) anywhere that would allow oil to mix with water, oil pan gasket ??
Some of these might seem odd, but remember that oil is heavier and will always sink back to the bottom of the engine, once water has infiltrated the engine, traces of it can be found as high as the oil filler cap.
I have just had the engine removed and am performing the following work.
Heads R and R'd
New oil pump, water pump, thermostat/impeller housing, exhaust manifolds are being acid washed, double roller timing chain, new timing chain cover, oil cooler....and installing a fresh water cooling system
Salt water is NOT a boaters friend under ANY circumstances, and extreme care and maintenance will become your best friend. I am lucky to be able to remove my boat from the salt water environment occasionally and cant imagine how the boaters who cant deal with the abrasive conditions...
Hope some of this helps