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Discussion Starter · #1 ·
How would someone go about strengthening the transom of there boat to accept a higher HP motor? Im not talking much more. Only on a 12' Aluminum with a rating of 10hp. I would like to go up to a 15hp or possibly 20hp.
How would it be done to strengthen the transom?
Thanks
 

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Add plywood to the transom! But if you are going from a 10HP to a 15Hp I don't think you would necassarily need to unless your transom is in need of repair.
 

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Discussion Starter · #3 ·
Thanks, yeah probably wont need to do anything but a peice of plywood sounds like a start.
And then what? Glue it to the boat?
 

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To really beef it up, cut a piece of 3/4" plywood down to shape, coat it in an epoxy resin coat (makes the wood last substantially longer in the water) then bolt it to the original transom. 4 bolts should do just fine. If you added that I would think that a 20hp wouldn't have any issues.
 

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Look at the top corners , that's were the issue will be.... :beerchug:
 

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Transom strength is not the only factor of why boats are rated for a certain horsepower. You may be building a monster. I saw a 12' fill with water when a fellow tried a 20hp on it. He turned sharply and gave it some gas. Back corner on the inside of the turn dropped low enough to let the lake in. There just wasn't enough boat for the motor. Not saying this is your case but give it a thought.
 

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The power may not be the problem,,the extra weight of the larger engine may be too much for the gunwale(side) depth...
A lot of 10 hp motors can be easily tweeked to 15 hp without adding any extra weight..
Justa bigger carb ......
I know my older 12' harbor craft wouldn't have liked the 120 lbs of a 15 hp 4 stroke hanging off the back end in addition to my less than Twiggy sized body sitting in the rear seat... :-\
Taking the plunge under the waves when out on the water can ruin a good day of fishing fast...
 

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Discussion Starter · #8 ·
Ok let me beak it down for everyone. I am thinking that this strengthening transom idea may not be necessary. I am looking to purchase a 04 15hp Yamaha. This particular year the 9.9's & 15's weigh the same. So I dont think I will have any problems. If I were to simply throw any 15 or 20 on the boat then all the points above would be right.
I think I will be ok putting that Yamaha on my boat. What do you guys think?
 

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Sometimes a few gussets is a good idea if you are worried about a problem, more power can stress the boat.
I have done transom upgrades and always add gussets at the back corners.
 

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The whole boat is tied together and needs to take the extra omph so the gussets are the best plan and they should be in the corners to tie the transome to the side and from the transom to the floor as well. This should also be done in such a way to control the hull flex. Most Hp ratings (especially on US built boats) are based on the amount of floatation in the hull. What brand and model boat do you have? No mods may be neccessary to go to 15 Hp.
 

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Cascademarine is exactly right....Infact this is what I did to my 16fter to beaf it up for tubing and
water skiing. I also added a bridge about one foot up and straight across from side to side. This stiffened
her right up and still allowed the front end to flex freely...... :beerchug:......Marko
 
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