I know on a full size boat raising the motor to get the cavatation plate up higher will increase the performance of a boat but on an RC how do you determine at what height to set the plate or is it by trial and error?

I'm not sure what you mean, but from what i understand, i would keep the boat's prop submerged and keep the shaft as parrelel to the bottom of the boat's hull as possible. If you're talking about where to place the engine (lower, higher) then i'm stuck.

I hope that helped.

full size differ from RC.
it depend on what kind of boat you have.
Most rc boats are either sub drive or surface. a Sub drive is usually under the water but can some times be off the transom ( like full size boat)
and then the other is surface drive which there is no cav plate.


that is a surface drive. with no cav plate.

here is a model of a #6 dry sump. which is on many real boats including mine. this you can trim just like a real boat.

this is a submergs drive. which is just like ones on a ski boat.
you can not change very much on this but the angle of the rudder to lift the bow out or lower the bow