Beefing up transom to take 150hp Outboard

[willy13]

My 24' pontoon is rated for 115hp. It currently has 40hp. I am tempted to beef up the transom with some triangulated braces that would carry the forces better to the pontoons. My target top speed is 30mph, and I do not think 115hp would do it. From reading other posts it looks like 24mph is what I would get with 115hp.

Considering the size of the boat and after seeing the massive engines that are put on fishing boats, I am convinced the coast guard hp limit is only related to the transom strength and not a safety issue from over powering a small boat.



My first thought is to install a brace between the bottom engine mount on the transom to the upper portion of the pontoon. This would keep the transom from twisting when turning the boat. I figure the transom is already secure enough when the boat is going straight. Its the forces put on the transom when turning that make me concerned. Thoughts?

My other concern is that 150hp won't be enough motor to push the boat to 30 mph. If I can't reach that speed, I do not think the extra $2000 in motor and time for fabing would be worth it. Adding a third pontoon would be great but out of my price range, especially since I would need to get a new trailer. All comments appreciated, and thanks for looking!

[Bamby]

I'm not trying to rain on your parade, but proceed with caution unless you've got lot's of capitol to work with. By the waterline appearance your pontoon is currently at it's ideal weight of the pontoons being half submerged. Another few hundred pounds right on back could not help with this situation.

A boating friend has a fun-toon that I'd swear is off the same production line. Anyway he had to re-power his just awhile back. With his old engine he could trim his engine clear up without clearance issues. Ain't so with his new engine which is a 90 hp etec. He now hast to watch very carefully that he stops it before he grates the engine cowling into the sundeck frame. He hasn't done it as yet but it's only a matter of time until he actually modifies his sundeck or buys a new engine cover or ends up doing both.

IMHO: The reality of it is you probably should be shopping for a third pontoon with an engine transom for your boat. It would allow you to move the motor back a bit for engine clearance and allow some additional and maybe needed flotation for your boat.

[willy13]

No worries on raining on my parade! I am hear for opinions.

I am planning on modifying the sundeck to clear the engine when its tilted up. Clearly this boat was design for V4 two-strokes instead of the inline 4-stroke that are mostly available today.

It is tempting to finance a new triple pontoon, but the best part of this pontoon is its hard top. The kids, and me too, have a blast jumping off the top. While I have not looked that hard, it seems to me that these are not common on new pontoons these days. And would probably add substantially to the cost.

[Bryden24shp]

Bamby>>>He now hast to watch very carefully that he stops it before he grates the engine cowling into the sundeck frame. He hasn't done it as yet but it's only a matter of time until he actually modifies his sundeck or buys a new engine cover or ends up doing both.
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All he has to do is adjust the limiter under his motor, so it will stop short of hitting his sundeck. Very simple to do. It should be in his owners manual.

Willy13, have you priced out a middle toon to mount that 150 on? May be worth doing some leg work on...

Bryan

[Bamaman]

Like was said, it looks like the weight of your motor is perfect for your boat. If you didn't have weight of the hardtop, you'd be good for a modern 115 hp motor.

My 1985 Starcraft has a Yamaha 115 hp 2 stroke, and it accelerates like a bass boat--but hits a speed wall @ about 28 mph.

To get any pontoon faster than 25 mph or so, you must either have serious horsepower or lifting strakes to get the nosecone out of the water. Strakes are seldom put on older boats and motors less than 90 hp.

You're just in a dilemma.

My new Bennington really performs well, and it's so far been a joy to own.

[jimrs]

I think that I agree that your pontoons are a bit on the small side. New motors are a lot more weight than your toon can handle.

New Merc 40-60hp 260lbs
New Merc 150hp 510lbs
New Merc 150hp 451lbs

The 510lb is Super Charged but that is a lot more weight for your small pontoons to carry in the back of your boat.
Which sits kinda low now according to the water line on your toons.

[willy13]

Well its looking like the 150hp Yamaha is going to be $3500 more than the 115hp Yamaha, so that fact may have made my decision for me. I did not expect such a price difference.