Rebuilding pontoon into a tri-toon

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MCarter81

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I got an 18ft Lowe Pontoon boat from a friend that let it sit and rot. I have stripped everything down and am currently waiting on a guy to finish welding up a center toon with a built-in transom that he says will be rated for up to 300HP. I plan to rebuild it as a center console fishing machine that would also be able to pull tubes when desired. My question: On a smaller/shorter tri-toon what would be a reasonable size motor to install? I am thinking 200-225HP but don't know how much is too much.
 

jhande

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I'm certainly no expert but I would think that total weight would need to be part of the equation not just length alone.
 

Scott Danforth

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here is some light reading.


keep in mind, unless properly designed, you may not be any faster with 200hp than you would be with 50hp on a pontoon. you need to get a displacement hull up on plane. that means lifting strakes, etc.
 

ahicks

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here is some light reading.


keep in mind, unless properly designed, you may not be any faster with 200hp than you would be with 50hp on a pontoon. you need to get a displacement hull up on plane. that means lifting strakes, etc.
+1

There's a lot too this, including the weight of the motor. That said, you don't want to pull a tuber over something in the low 20's anyway (too easy to get hurt coming off!), so it doesn't need to go THAT fast.
 

MCarter81

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Thanks for that article. That was helpful. I should have included the size of the pontoons. 20.5x22in U-shaped and they do have lifting strakes. I was unable to find any original rating information on the railing I still have. Based on that article and with some math, something in the 150HP range sounds more appropriate. I appreciate the input.
 

ahicks

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I'd be tempted to go with the biggest 4 cylinder motor I could get my hands on - to avoid the extra weight of the 6 cylinder engines.

Are you thinking new or used motor? 2 stroke, or 4?
 

MCarter81

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Definitely thinking used. And a 4-stroke would be nice as they are quieter, but if I'm not mistaken they are generally more expensive and weigh more also.
 

Scott Danforth

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Thanks for that article. That was helpful. I should have included the size of the pontoons. 20.5x22in U-shaped and they do have lifting strakes. I was unable to find any original rating information on the railing I still have. Based on that article and with some math, something in the 150HP range sounds more appropriate. I appreciate the input.
remember, you have a displacement hull. plenty of pontoon threads on here where someone pulls a 50hp off to install a 90hp and the speed is the same, however the fuel consumption and noise are increased. if you are planning on getting the pontoon to go up to 40mph, it probably wont.
 

ahicks

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remember, you have a displacement hull. plenty of pontoon threads on here where someone pulls a 50hp off to install a 90hp and the speed is the same, however the fuel consumption and noise are increased. if you are planning on getting the pontoon to go up to 40mph, it probably wont.
And then again, there are those of us that replace a 40 with a 90, and are able to pull a tube pretty easily! Lightly loaded the boat is good for 25mph (per GPS). 24'boat w/90 Honda

I do acknowledge the fact that to get that kind of performance with a 'toon, you need to keep it light. It's not going to do that loaded down with heavy home made furniture and 9 people on it.....
 

emilime75

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One thing to consider is that if you boat on any public bodies of water, the coast guard or whatever entity patrols said body of water could have an issue with your boat not having the ratings and capacities sticker, or an engine that surpasses it, regardless of you adding the 3rd toon.

Beyond that, how fast do you want to go? The consensus that I've come up with while researching pontoons is that for a tritoon of about 22-24' in length, you'd want at least a 150 to see speeds of around 30 - water conditions and load dependent. For an 18', a 150 would be in the mid 30s, roughly. A 115 around 30-35, likely. Obviously, these are very rough numbers and there are a ton of factors that come into play, especially on pon/tritoons. For instance, just having your bimini up and open will slow you down significantly, as will growth on the toons if you intend to leave the boat docked in the water.
 

Gardog66

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It always seems like there’s always someone on every forum that wants to make a pontoon a speed boat. I have a 1990 Grumman 20 foot pontoon and with a 40hp Johnson 2 stroke on 23 inch logs will do 24 mph with 4 people. If I put a larger engine on it I know I won’t gain anything but a higher fuel cost. I can boat most of the day on 12 gallons of fuel. And that’s great.
 
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