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  1972 SPORT 13: Mounting Outboard to Transom

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Author Topic:   1972 SPORT 13: Mounting Outboard to Transom
okish posted 08-22-2015 02:01 PM ET (US)   Profile for okish   Send Email to okish  
Hi. [I] have a 1972 SPORT 13 with the 15-inch transom and the sink-style splash well. The transom on this hull has not been drilled and is in great shape. The motor that [I] have is a c.1990 Tohatsu 30-HP that has a set of clamps, and only two mounting holes that are slightly below the clamps and are 8-inch apart. The mounting holes are at a proprietary location compared to the standard mounting pattern.

Should I drill [holes in the boat's] vintage transom? Or, find another engine? Or just run the clamps? I feel that I should drill and clamp. Here are the URL's to some pictures of the boat and the motor

Un-drilled transom
Side view of boat hull showing sink splash well

You can see the bolt holes right above the tilt pin
Wide shot of entire engine

jimh posted 08-22-2015 02:27 PM ET (US)     Profile for jimh  Send Email to jimh     
Use of the 1990 Tohatsu outboard engine should be based on its shaft length. Is that engine a 15-inch-shaft model?

People used outboard engines with clamp mounting for decades. You can add a wear plate to spread the load of the clamps over a wider area and stop compressing the transom.

contender posted 08-22-2015 02:46 PM ET (US)     Profile for contender  Send Email to contender     
Jim is correct, I would use some type of plate to spread the load/connection of the clamps. Either a thick rubber gasket or I have seen leather used as well. Using the clamps only you need to check them all the time, they come loose, I use to tie mine together so that they can not unscrew. I also had a safety chain to the inside lifting eye to the engine....good luck
okish posted 08-22-2015 02:57 PM ET (US)     Profile for okish  Send Email to okish     
Yes, it's a 15" shaft. I bent up a 1/4" thick aluminum plate to match the curvature of the inside of the transom so that the clamps will spread the load better. I was planning on using 3m 4200 to seal the plate to the inside of the transom and tightening the clamps to that. If you guys think that the clamps are enough , i will refrain from drilling the transom. Would you guys recommend using any type of shims to compensate for the curve of the transom or just let the brackets sit slightly crooked?
jimh posted 08-22-2015 05:05 PM ET (US)     Profile for jimh  Send Email to jimh     

boatdryver posted 08-23-2015 01:18 PM ET (US)     Profile for boatdryver  Send Email to boatdryver     
Our sailing club used the "Transadapter" (see link below) in order to mount a 20 inch Etec to a vintage 13 ft Whaler with the notched transom.

This approach has worked well for 2 years now.


okish posted 08-23-2015 01:41 PM ET (US)     Profile for okish  Send Email to okish     
Thanks Jim, but i have a 15" motor.
contender posted 08-23-2015 06:36 PM ET (US)     Profile for contender  Send Email to contender     
okish using an alum. plate (3/16) for the bracket is slippery, you are putting metal to metal and it will move some. You need to put something under the clamp, or mount the engine and see where the marks are made on the plate, remove the engine and plate and have a machine shop take 1/16 off the area of the clamp (fly cut I think its called), Now the clamp has no were to move and will stay inside the area...And yes I would glue the plate to the transom but I would use 5200, the only thing is it will cover your hull number unless you do a cut out in the plate for the number...

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