I know that a transom on a normal hard boat has a tilt somewhere between 10 to 15%. I'm having some pipe bent to make a motor mount on my 18 foot round raft and am being advised the curve should be 90 degrees - which will put the transom plate vertical (straight up/down).

My new motor mount frame will be attached to the main rowing frame that I'm hoping will lessen the stern's tendency to dip/drop and I'm now concerned that just putting around at idle, that the stern might not drop much at all; therefore, a vertical transom plate may not give me the rake needed for normal prop operation.

So many variables I know - just looking for suggestions on what angle I should order the curved pipe that will be used to hold the transom plate. In other words, what transom angle to shoot for when designing the motor mount? Many thanks.

P.S. - I'm using a 6 h.p. Tohatsu 4 stroke which has 5 outward tilt positions.