My opinion is there is nothing lost in the 53 to 63 to 63S versions. I believe as with all YS engine generations each change is for the better.

I'm not sure how much luck you will have with 63's or even 53's in a boat application. YS engines are designed to be very powerful but anyone that owns one will tell you that cooling is important with any YS engine. The pressurized fuel system can be very heat sensitive. The 63FZ was changed to the 63S because the type of model the engine was being put in. Hovering and 3D doesn't allow much cooling, and when the engine gets hot it doesn't respond as well. Moving the pressure regulator external of the engine case helps to keep the fuel cooler before it enters the engine.

I don't say this to discourage you just these engines are designed around model airplanes that fly, and when they fly the air cooling them mis pretty important.

Troy Newman
Team YS Performance