My 1st pontoon. Need 3rd log advice

Marley marl

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Jun 28, 2015
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I purchased a 24ft Harris. It has 24' x 20" logs. I did a total restore. I made my own seating which I know added to the weight. It came with a 70hp Yamaha but I traded it for a 1989 mercury 150 black max with 17p ss prop. While reading posts in this forum, I may have too much motor for the boat. It actually doesn't move through the water as fast as I would like. When my rpm gets higher, it's seems like it loses its bite and doesn't continue to pull. I can slow down some and it seems to catch and push the boat. I have an opportunity to purchase 3 u-shaped logs.....23'L x 21"W x 22"H. Would it be better for me to get these logs and make it a tri toon while having the center log with the transom conversion or should I just scrap the idea all together? I'm wanting to pull a tube, maybe a skier if need be and have a better ride.
 

ron nh

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Sep 19, 2014
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yea, 20" tubes on that size boat with that size motor is just to much weight. are you sure there 20"? if thats the case I would buy new logs.
 

Marley marl

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I was thinking along those lines. Would the three I mentioned in my initial post work or should I find larger dual diameter logs? If so, how large?
 

ahicks

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If I were going to the trouble of replacing the logs, they would have lifting strakes, especially if I were using that kind of power.
 

ron nh

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I agree, get 25" logs with strakes and underskin it while your down there if its not already done. with a 150 strakes and skin you'll love the ride. and of course three logs if you can swing it, you'll have a 40mph tri-toon. or pretty damn close. I don't know much about the u-shape and boyancy for there size, but, I'm sure it would be a huge improvement over current tubes.
 
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ahicks

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Thinking about this a bit, a 25" 3rd log with lift strakes combined with your existing 20" might make for an interesting boat.
 

Marley marl

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I was looking at the u shaped toons. They are in great shape and wants $2250 for all three. Didn't know if they were worth it with the motor I have. Although they are 21"W x 22"H, it's still smaller and has less buoyancy than 25" dia tube. I know there will be extra weight along with the 3rd toon but with their size, would it work for me?
 

1983 ercoa 21'

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Jan 12, 2014
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If there is nothing wrong with the tubes you have just find a center toon if the diameter is a little bigger that's fine because you normally want center log about 5" lower. Mine is 8". It's all in the money you want to spend. Most u shaped toons are foam filled and if they have or get wet on the inside it makes for alot of work if the foam absorbs the water.
 

Grandad

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I traded it for a 1989 mercury 150 black max with 17p ss prop. While reading posts in this forum, I may have too much motor for the boat. It actually doesn't move through the water as fast as I would like. When my rpm gets higher, it's seems like it loses its bite and doesn't continue to pull. I can slow down some and it seems to catch and push the boat.
This kind of performance is what I would expect from a "spun" prop hub. May be worth investigating before getting too much invested in other solutions. - Grandad
 

HotTommy

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Marley Marl,
What follows is mostly theory that may not translate precisely to real life operations, but it might help you decide what to do.
1. All floating boats sink down into the water until the weight of the water displaced by the hull equals the weight of the boat. If a pontoon boat has its weight evenly distributed on two symmetrical pontoons, the depth of each pontoon will indicate the weight of the boat. The depth will also reflect the shape of the toon. A fatter, longer toon won't have to sink as deeply to displace enough water to support the boat.
2. Unless it has some lifting mechanism (i.e., strakes or flat bottom toons), it pushes its way through the water when underway. The more of the toons that is beneath the surface of the water, the more water is has to push, so the more power it takes to go at any given speed. A good indicator of how much power it will take is the cross sectional area of the part of the toons that are below the surface of the water.
3. If you add a third toon just like the other two you will add weight and more lifting volume. The added weight means you will need to displace more water total, but as the total weight is being supported by three toons rather than two, each will sit higher in the water than before. But as the engine is pushing more weight that is displacing more water, it will likely be slower.
4. The bottom halves of the new logs you are considering are effectively round, and I assume your boat will not be heavy enough to push them more than half way into the water most of the time. So we can compare then with your current logs as follows. A 21" log has a cross section that is about 10% larger than a 20" log. A 23' long log has about 4% less volume than an identical 24' log. So each of your new logs displaces roughly 5% more water than your current logs. If you replaced two for two, I doubt you'd notice the difference. Replacing two with three will cause your boat to sit slightly higher, but not likely run any faster.

Bottom line: I suggest you do as was suggested above. Focus on the engine/prop problem first. Then, if you want to go faster, get logs that will lift your boat when it is underway. Just changing from two logs to three likely won't help.
 

1983 ercoa 21'

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I agree with the slipping prop there is a way to test to see take the prop off make a mark from center hub to outer hub and put it back on and run it till it acts up then remove it and see if it's still in line if it's not then you need to replace prop hub. As to the two log or three log . I don't regret going to three log yes it will slow you down a little bit but the advantages for out weight the losing a few mph . Your transom isn't built to handle a 150 if you choose to stay with just two logs then buy a transom that is rated for 150 and I also suggest you add a couple more cross members to the transom area.
 
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