If I were to put a mercedes diesel in a sailboat in a saltwater enviroment I would choose a non turbo model, galvanize the oil pan, and cool it with a keel cooler. If you dont want to affect windward performance when sailing dont go with anything heavier than the origional engine ( heavier engine and you'll have to remove some ballast to get her to sit on her original lines and this will affect windward performance). Also take into account that it doestnt take much horsepower to push a 40' displacment hull. If you go too big it will be underworked and run too cool resulting in problems.

I just purchased a 83 240d with 140k for $200. The plan is to put the engine in a friends boat that we are going to turn into a sternwheeler. The engine will be keel cooled and drive a hydraulic pump for the sternwheel.

If you were talking about putting one in a trawler yacht weight wouldnt be a consideration. My 44' Trawler's engine and gear weighs 3800 lbs!, and generates 80hp @ 1600 rpm.

Too many cars, tucks, motorcycles, and boats to take the time to list.