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Author Topic:   13' Sourpuss transom

mgrl posted 11-26-2002 11:03 AM ET (US)
I have a 1970 13' Sourpuss that I'm in the process of repowering from a 1968 40hp Evinrude to something a little smaller/newer. It has a cut out transom of 17 inches. Looks like for newer engines that shaft choices are only 15" or 20". I'd appreciate some thoughts about how to accommodate the differences of the shaft/transom.
Tom W Clark posted 11-26-2002 11:29 AM ET (US)
mgrl.
Your boat has a 15" transom and as such requires a 15" shaft motor, though you could use a 20" shaft motor if you were to add a bracket or "jack plate" to raise it up.
Transom height and shaft length are not precise measurements and do vary slightly from product to product. The relationship between motor and hull can be varied for different performance characteristics. This is why motors typically have different mounting holes in the mounting bracket.
But the main reason why you think your transom is 17” is that you are measuring along the transom instead of measuring the vertical difference between the top of the transom and the keel. The 13’ Whaler’s transom has quite a backward lean to it and thus the distance along it (the hypotenuse of the triangle) is significantly greater that the height (altitude).
In other words, if you put a straight edge along the keel, projecting out from under the stern and measure from the top of the transom perpendicular to the straight edge I think you will find it is quite close to 15”.
mgrl posted 11-26-2002 11:43 AM ET (US)
You're right. I was measuring it the wrong way. I just went out and measured it as you suggested and it is quite close to 15". Thanks for clearing that up.

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Author	Topic: 13' Sourpuss transom
mgrl	posted 11-26-2002 11:03 AM ET (US) I have a 1970 13' Sourpuss that I'm in the process of repowering from a 1968 40hp Evinrude to something a little smaller/newer. It has a cut out transom of 17 inches. Looks like for newer engines that shaft choices are only 15" or 20". I'd appreciate some thoughts about how to accommodate the differences of the shaft/transom.
Tom W Clark	posted 11-26-2002 11:29 AM ET (US) mgrl. Your boat has a 15" transom and as such requires a 15" shaft motor, though you could use a 20" shaft motor if you were to add a bracket or "jack plate" to raise it up. Transom height and shaft length are not precise measurements and do vary slightly from product to product. The relationship between motor and hull can be varied for different performance characteristics. This is why motors typically have different mounting holes in the mounting bracket. But the main reason why you think your transom is 17” is that you are measuring along the transom instead of measuring the vertical difference between the top of the transom and the keel. The 13’ Whaler’s transom has quite a backward lean to it and thus the distance along it (the hypotenuse of the triangle) is significantly greater that the height (altitude). In other words, if you put a straight edge along the keel, projecting out from under the stern and measure from the top of the transom perpendicular to the straight edge I think you will find it is quite close to 15”.
mgrl	posted 11-26-2002 11:43 AM ET (US) You're right. I was measuring it the wrong way. I just went out and measured it as you suggested and it is quite close to 15". Thanks for clearing that up.