A friend of mine has a 20 year old Crusader with 900 hours. Last week his piston broke off and the rod punched a hole through the cylinder wall. The mechanic said it happened because he was low on oil. Would being 2-4 quarts low on oil contribute to this engine failure?

Sure, its possible that the motor ran out of oil in the pan faster then the oil could drain back down to the pan causing serious engine damage...

900 hrs? I would bet that that pistions just said enough is enough I'm out of here! I am sure the "low" oil help him pack his bags.

a motor with 900 hours has given its all, it was probably pretty tired, but how did he let the oil get so low i check mine everytime i go out.

Although 900 hours is a lot for a boat, the low oil would be the culprit for a major engine meltdown like that.

Was the rod intact?

Heck, I check it everytime I turn the motors off or park somewhere.

Did the rod break at the piston pin or did the piston come apart? That is the way it sounds when I read your post, if so I doubt the oil had anything to do with it. If the rod broke near the rod journal (close to the crank) then I would be more likely to suspect a low oil/ oil pressure problem, especially if the rod journal was black and burnt looking which would have been the result of a spun bearing.