24" dia x 36" long pontoon design help pls

Question? I am going to face my pontoons with the 36" length facing the forward movement of the boat in lieu of the norm 24". I get about 200lbs lift with each 24" x 36" pontoon at half down. There will 6 on both sides and a total of 13 on this 24' x 7' fishing pontoon boat. I am doing this for better water flow beneath the pontoon and stability "I Think" . The back section will have 3 pontoons with the middle 36" and the 2 sides 24" The middle pontoon will create a tunnel effect on the motor. " I think". What do you see? Thanks

 

This is not a clear enough description for my feeble mind to grasp. Are you suggesting that you will use six 24 inch by 36 inch tubes on each side? And the 13th one will be somewhere in the middle? I cannot reconcile the arithmetic with a 24 foot boat.

If that is what you are doing then leave the middle tube out altogether.

At 12 inches immersion you are going to have about 1750 pounds of displacement for each 18 foot side or a total for both sides of 3500 pounds at half immersion. You do not want half immersion of the pontoons. Less is better, eight inches maybe, then you will have some good reserve. At 8 inches you will have about 1150 pounds per side or 2300 all up. But if the pontoons are 24 feet long the numbers will increase by a factor of 1.33 Which is it?

Describe what you are after...Are you looking for speed? For stability? for fuel economy? How much power will you put on the boat? What will be the all up weight of everything...... boat, motor, passengers, gear, fuel, water, etc when in cruise mode?

More details please.

 

Front View of the boat, I would see the 36" rounded side of the pontoon. Side View, the 24" dia.
Mainly I am asking, How will the boat perform when taking off and getting on top of the water with the pontoon turned side ways (36" round side facing the forward movement). Will the more rounded side of the pontoon get the boat on plane faster or run faster.

 

If I understand what you're describing, the maximum speed you could ever get out of this thing would be less than 3 mph. While the 12" radius may seem like a friendly shape to push into the water, the 12 inch radius on the backside will hold water against it and no lift will be generated. Regardless of horsepower, this thing couldn't plane.
Gerald

 

So you can't use several short pontoons spaced apart?

 

My thought was longer pontoons sometimes are overkill. 90% of the time you don't have 15 people on your boat. I like the length but it seems like a waste aluminum. How long should a pontoon be to have good performance?

 

Post a photo of your boat or a drawing of what you're thinking, as I'm still a bit confused about your ideas. At first glance, it appears you don't have a lot of hydrodynamic understanding, as pontoon lengths aren't "reserve" just in case you have 15 people aboard. Also as mentioned, pontoon shapes aren't well suited to high speeds.

 

My late night foggy brain take from the description is, the pontoons will be assembled believe it or not with the axis of each 24"dia. X 36"lenght pontoon section transverse to the fore and aft run. Visually this would be like assemblying 45gal. fuel drums side by side and not end to end forming the lenght of each of the pontoons. The thinking as stated, there would be low resistance to movement presented by the rounded section of each drum as it is being propelled forward with it's axis transverse to the direction of travel. Ok--time to go to bed as this is mind boggling --I have visions of Englands WW2 spinning dam buster bombs. -----

 

That's the way I understood it when I responded above.

 

Okay, I have a better idea, transversely arranged drums, the length desired. Yep, all kinds of drag there, with a bump every 24". You'd be hard pressed to get 1.35 S/L ratio without a few hundred horse power. 5 to 6 MPH would be the very best you could hope for (1.0 - 1.13 S/L), with 4 - 5 MPH (.85 - 1.0 S/L) being more realistic with the associated drag of the lumpy bottom. Assuming it doesn't weigh all that much, you should get this speed with a 20 HP outboard.

Lastly, why 7' of beam? 8' would offer more deck space and is within trailering width limitations.

 

This is a pontoon boat i just finished. Look to the rear the "blue" 36" x 24" pontoon with styrofoam I processed inside. These blue pontoons are hard as a rock and will not sink even if cut in half. I can force both into the water for max lift and stability while in my slip. I don't know what to expect while running? A video will show the results.

This is a very low cost pontoon but how do you design it for performance? Most people could afford this larger boat and it is very very safe.

Par, is that the direction you where talking about? Would a flat 24" channel on the bottom connecting the pontoons together do the trick? ears up or down?

 

What makes it so "very very safe"?

 

I am talking about a fishing boat using all blue pontoons. If it turns over just get inside. It will not sink.

 

By using the word performance, I will assume that you mean that it should go fast without using collossal horsepower. Design for performance by forgetting the round pontoons and making them with fairly wide flat bottoms and sides.

And by all means, put the notion of sideways cylinders in the verifiably counterproductive idea file.

 

Yep, the drums aren't going to be related to any level of preformance, by the normal means of describing it. Pontoons are fairly easy to build and again forget about the cylindrical shapes. Most of the design clues should come from, well, preformance power craft. There's a number of ways to go: flat bottom, slab sided, long, lean boxes which will be efficient and require the least amount of power, to asymmetric V'd shapes to milk the last ounce of ability out of the twin hull configuration.