transom height question

[Duratech1]

I have a 1958 15' duratech aluminum boat with a 1970 18hp evinrude, and im considering purchasing a 1975 40hp evinrude. Right now it is 23" from the transom top edge where the motor hangs from to the center of the prop. The new motor measures 29" from the same points. My transom dips down in the center 6" in the middle where the motor hangs which is exactly what the difference in length between the two motors. Is it normal and acceptable to build a new transom straight across to make the new motor prop sit at the same height? My concerns are strength and handling. Id assume youd want to use nothing less than pressure treated plywood with the metal plates already there for all extra support? Id like the extra power to potentially do some tubing and water skiing. New motor currently has no prop and I know nothing about them, any tips on correct pitch would be appreciated.

 

[roscoe]

No Title

No it is not normal to have to build up your transom.
Your boat has a 15/16" transom.

You need to find a motor with a short leg, made for a 15" transom.

It is a lot of work to build up a transom properly.

Easiest way would be to purchase a manual jackplate.


No, you do not use pressure treated ply.
The chemicals in the wood will react with the aluminum in the hull, and cause corrosion.


Waterskiing is possible, but tubing, not likely, as the drag is enormous.