A question that has been asked before

[radtech]

however since I am new to this forum I will go ahead and ask this question again. I bought a 20' pontoon and tore it down to the pontoons and rebuilt it. The pontoons are 19" in diameter and I would like for it to be more bouyant than it is. I am running a 70 horse 1973 model evinrude and it does run real good. It is 5hp before max for the boat. I can get 8 people on the boat before the pontoons in the back are just under and if we are loaded with coolers or just somemore poeple the front rides low in the water. I have seen other boats in the same predicament. Is there anything I can do to make my pontoons more bouyant? Anyone's help would be greatly apprecatied.

[alan white]

Here is a case where not much can practically be done, and here's the reason: A pontoon boat, unlike a normal boat, has the same bouyancy fore and aft. The engine sits on the end, and no doubt most weight aboard is sitting a ways back from the bows.
Short of going to a smaller, lighter engine, or relocating the engine further forward, trim can only be shifted by putting more cargo and people forward.
Batteries like to be near the starter, but bigger cables would allow that weight to be brought forward.
My quick answer would be to sell the boat and get a bigger one if this weight-carrying is important to you. Maybe someone else can suggest another course of action, but I think any big modifications would be a waste of time. You might look into a 24 ft boat. Otherwise, make do and save your money and energy.
I assume this boat has strakes of some sort, angled to provide lift. I don't know if something could be done in that area---- wait and see who pops in to address that question.

Alan

[Trevlyns]

You cannot increase buoyancy of a fixed object (pontoon) without increasing its volume. Filling it with compressed gas, helium etc will do nothing… It’s physical size has to increase. I’d go for additional (or larger) pontoons.

I saw a pontoon boat in a recent issue of Soundings "Trade Only" that had three pontoons instead of the normal two. I would have thought there would be a lot of drag with such an arrangement but apparently it works. I think the bottoms are modified to be hard chines ,though. I've tossed the issue so I can't help much more than to say that I think the concept was developed by somebody like Morrelli and Melvin- good multihull designers. Might be worth some research.
I haven't been able to find the manufacturer of the boat I saw but here is a site with some info:
JC Pontoon - Manufacturer of Evolution, TriToon, SunToon, NepToon Pontoon boats.
Address:http://www.jcpontoon.com/hull.html Changed:9:00 PM on Thursday, June 7, 2007

[marshmat]

radtech,
Firstly, welcome aboard boatdesign.net - I'm sure you'll find this place both entertaining and useful
Now as to your pontoon rig. I see three possible solutions to your dilemma.
(1) Limit your total crew/cargo weight to what the boat can actually carry in its current configuration;
(2) Sell this boat and buy one with longer, wider pontoons;
(3) Add a third, central pontoon to the current boat.
The first option is the cheapest- learn to live with it. The second is the easiest way to increase your payload capacity. The third lets you keep the same boat but is an iffy endeavour and requires that you be able to find a pontoon of the same length, diameter and shape as the current ones, and that the boat has appropriate structure for mounting it.

[alan white]

A thought occurred, and it's just an idea, but if the aft ends of the two pontoons were legthened by cutting the caps off and inserting (heliarc welding) two 18" by 3 or 4 ft sections, the boat would gain some added buoyancy. This would also put your engine and general load farther forward.
While this might be a next winter project, it is not an expensive job if you do all the basic work yourself. It might even increase your top speed.
Others might weigh in on this idea, since I'm no navel architect. I might be missing some factor that would come into play.