50mph Pontoon

[Egret189]

Hi, everybody.
My weird long-time fantasy boat build has been a home-made high performance pontoon boat. Recently I've decided that this is a project that I'd like to pursue. Maybe you folks can send me some wisdom or have tried to do something similar.
THE PLAN:
A) To find a ~20ft pontoon with the larger style pontoons with or without an engine. Probably mid '90s is the era I'm thinking. I've owned a few Sun Tracker "Bass Buggy" 'toons and think that it would make a good platform.
B) Find an aluminum welder to add reinforcements wherever needed. I am thinking the engine mounting bracket would be a good place to start. I would also then have him add planing strakes as are found on the newer pontoons to add some planing capabilities. (The hydrodynamics involved here may be where you can help me).
C) Mount an engine profoundly larger than that for which the boat was designed. The engine I have in mind is a 150 or 175 Johnson Fastrike (60* Block). I really like these engines for power/weight ratio.
With all of this completed, I am hoping that the end product will be a somewhat cheap pontoon boat that is capable of cruising at 30mph or so. My family loves pontoon boats for the room and comfort but the rate of travel leaves much to be desired. I know that I could buy a deck boat but that sort of ruins the novelty for me. I realize that this build would involve a decent amount of modification to the pontoon boat itself. I just want to know if I am overlooking anything crucial to the success or failure of this endeavor. Thanks for any and all input!!
Jake

 

[HotTommy]

I'll be curious to hear what others say about adding strakes to pontoons. I recall reading that it took some trial and testing by the manufacturers to get the shape and locations of the strakes right for each boat/engine combination. ... If you haven't heard of or researched the "Water Glide" give it a look. It's an add on center log that is supposed to lift the boat out of the water more for higher speeds and better MPG. ... The top speed of virtually any vehicle occurs when the thrust provided by the engine is matched by the drag on the vehicle. On a pontoon boat the major sources of drag are 1) the logs, 2) the engine/prop, the top of the boat pushing through the air. So think about the fences, furniture and the top too. Every bit of weight pushes the logs deeper into the water increasing drag. Every object catching wind increases drag.

P.S. As you mentioned doing this cheaply, let me note that the rule of thumb for outboard motor gas consumption is one gallon per hour per ten horsepower. So running your planned boat at top speed will cost you about 18 gallons per hour in fuel costs. That's not cheap in my world.

 

[Scott Danforth]

Google fast pontoon videos and you will come across a pontoon with triple 300hp mercs.

 

[Jeep Man]

You will do better with a 24' as opposed to a 20'. It will also handle the bigger motor better.

 

[BrianMc]

Jeep man is right on the length. I'd go with at least a 22',and a 3rd center transom tube. It'll be just as fast as a 20 and handle better. You might see 40-45 out of 150-175 hp if you keep the weight down. To run 50 your looking at a 225-250 hp.

Mine cruises at 30 mph real nice with a stout 150,and tops out 40-43 depending on load. It's homemade BTW. Have fun with the build.

 

[Egret189]

Tommy, for the planing strakes I'm planning to just emulate the design of one of the better known companies and hope it works. It seems that, in large part, ya'll are proponates of a larger barge. The only reason I selected the 20ft was because I was planning to base it off of the "party barge" by suntracker which is 20'6". It seemed like a very stout pontoon with logs that were larger than need be. That's the only reason I like that length. As far as having a third log, I am not sure how feasible that will be for me from a cost perspective. Really trying to keep costs low and I know that tritoons tend to demand a premium. Maybe you guys know something that I don't about this. What it comes down to is whatever I can find really cheap that will be reasonably well-suited for the build.

Brian, is there another thread where I can get some more information on your build? Did you add planing strakes? It sounds like you have achieved what I am shooting for ultimately.
Thanks for all of the input!
JAke

 

[BrianMc]

Yes, I added the stakes and the transom tube. You can pick up a transom tube several places online selling used or 2nds. Or have your fab guy add a transom to one you score. Maybe 1983 ercoa 21' will chime in here,as he just added a center tube to his.

My build thread link is below my posts in my signature .

 

[Jeep Man]

Tommy, for the planing strakes I'm planning to just emulate the design of one of the better known companies and hope it works. It seems that, in large part, ya'll are proponates of a larger barge. The only reason I selected the 20ft was because I was planning to base it off of the "party barge" by suntracker which is 20'6". It seemed like a very stout pontoon with logs that were larger than need be. That's the only reason I like that length. As far as having a third log, I am not sure how feasible that will be for me from a cost perspective. Really trying to keep costs low and I know that tritoons tend to demand a premium. Maybe you guys know something that I don't about this. What it comes down to is whatever I can find really cheap that will be reasonably well-suited for the build.

Brian, is there another thread where I can get some more information on your build? Did you add planing strakes? It sounds like you have achieved what I am shooting for ultimately.
Thanks for all of the input!
JAke

I own a 20' Party Barge. Mine is an '08 and the toons are in fact 18'. With the 2 ft. overhang on the rear, the deck is actually 20'1". Yes the toons are larger (26") but the additional length will give you more ability to plane, which is the ONLY way you'll even get close to 50mph

 

[jbcurt00]

50mph and pontoon don't fit what I think of as the whole purpose of a pontoon boat, but to each his own.

Good luck w/ your build

Post some pix when you get started

 

[HotTommy]

No Title

Jake,
Know that I am not opposed to the idea of adding strakes. I just wish I knew enough to do it myself. This picture will help illustrate my questions.

On this boat you can see that the boat is heavier in the back so the water line is not parallel with the deck. My boat had a water line angle similar to this my first season on the lake. I then put a much larger engine and new engine pod on it. It now sits even lower in the back and the angle is more pronounced.

Any permanently mounted strakes will also change the angle that they hit the water depending on the water line angle. It seems to me that would make the boat rise (plane) differently depending how your boat sat in the water. I also wonder how far down the logs to put the strakes. Put too far down they would try to act like water foils. Put too high they would not lift the boat enough to make much difference.

As you see, i have far more questions than answers. If you discover the answers through research or personal trial and error. Please post them. Thanks.

 

[1983 ercoa 21']

Well my build isn't as fancy as Brianmc but I done mine on a low budget and adding more and changing as time and money allows. I'm unable to upload pictures here for some reason but id be more than happy to help with any questions you might have Brianmc was very helpful in my build. My build started life as a 21' ercoa with hex toons I was unable too locate a matching third toon with in reason. I ended up using a blem from a Lowe toon the transom and strakes was already on I picked it up for 400.00 my outer toons are 20'6" the center one is 23.6 I mounted it so the fronts were about even and the rear sticks out the amount of the transom. I was running a v4 115 Johnson crank rated with a 13p it would run 30 ish depending on the load. I'm finishing up installing a strong 150 XP evinrude crank rated right now and adding hydraulic steering.

 

[Egret189]

Tommy,
I too have noticed a real lack of practical information on the subject of locating/fabbing and installing planing strakes on an old pontoon. Whenever this build does come to fruition, I will try my best to document information and hopefully assemble a comprehensive method of getting from point A (No Strakes) to point B (Strakes). As far as angle with relation to waterline is concerned, I do not know. My guess is that even though a boat may sit stern-heavy from the weight of the larger engine, at speed, the planing strakes would manipulate the boat to ride flat(ter).

1983, Thanks for chiming in. Definitely would be very interested in seeing your build. While Brian's build is a truly awesome feat of craftsmanship, I, like you, will be building a much more budgeted rig. Do you guys recon that the job can be done without a center tube? This, of course, would mean beefing my current mounting bracket to handle the extra power. I think that i can compensate, to some degree, for the absence of a centertube with larger lifting strakes. Maybe my logic is flawed. Also, did you fab your own strakes or buy them from a manufacturer?

 

[1983 ercoa 21']

Ok let me clarify the benefits of the center log.
my center log was already rated for 175 for what I spent for my log in not sure I could have bought or built a transom to with stand that.
the benefits of the center log in my case and how I see it are
better flotation
better handling a center log sits lower therefore providing a turn that leans to the inside rather than a lean to the outside pontoon turn. Which wouldn't be much fun at the speeds your wanting to travel.
I feel like when on plan my center log is what I'm riding on the outer logs are just barely in the water which I feel is reduced drag. I'm not sure how to explain the ride other than floating on air it's so smooth even in big wakes.

 

[1983 ercoa 21']

Brian is very helpful he will explain were and how to mount the straks . In my build my outtertoons are hexagon therefore already having the flat surface for planning my center toon already had strakes on it when I bought it .

 

[1983 ercoa 21']

Btw the last pan I seen rated for 150 they were asking like 800.00 for. What area are you from? I might be able to assist you with locating material needed.

 

[BrianMc]

Building an old toon to go fast might be as simple as hanging a big motor on it,but it won't take the abuse very long. Especially one with only two logs. Think about the forces at play here.

My XR6 has so much torque that it started to cave in the transom plate on my center tube. At speed it's carrying 2/3 of the toon out of the water. That's a lot of torque being transferred out. Where does it all go?

Think of it this way. Imagine hooking a long pry bar between your motor mount and transom. Place enough pull on it to lift half your toon off the trailer. Now bounce it up and down with the bar. Starting to sound like a lot of stress now,but that's what we're needing to overcome. And we're not done yet.

Now we have to consider the pounding it's going to take crossing waves at twice the speed it was designed for. The "racking" from angling waves is the worst. All that energy gets transfered through the little deck screws in the plywood that's trying to hold your frame square while the tubes are smacking waves at different times.

Ok, now let's look at the difference between a tritoon and a double. On a triple the center transom tube is the main hull. The deck is resting on top,and along for the ride. The outer tubes become more like outriggers stabilizing the deck. The frame is mostly carrying the outer tubes. The transom tube takes most of the abuse. A cylinder is a strong structure,especially when reinforced lengthwise.

On a twin tube all the torque from the motor gets transferred from the pod through the few crossmembers it bolts too. Not too big a deal with 90 hp that doesn't have the power to carry the bow when trimmed out. So, even after building the pod strong enough for the 150 you still need to at least double the number of crossmembers it bolts too. It's not just the weight of the heavier motor your carrying,at 40+ mph your also lifting the front half out of the water.

After contiplating that for awhile I can give you my take on strakes.

As far as the cost and time goes for the project. Figure everything then double it. Lol

 

[1983 ercoa 21']

Very well stated Brian.

 

[Silver Eagle]

You don't need a pontoon boat, you need a deck boat. Sort of like a pontoon boat but made out of fiber glass. Get one that is an I/O Some go as high as 300 hp. Easier to steer ,they have power steering..

 

[1983 ercoa 21']

Just going and buying another boat don't satisfy a mans need of building something and making it his own.

 

[HotTommy]

As far as the cost and time goes for the project. Figure everything then double it. Lol

My rule of thumb based on several projects is to do the best budget you can. Then double the cost and triple the time.