Pontoon Boat Design

Have recently aquired a pair of 24feet x 36inch diameter aluminum pontoons. Can someone provide the equasion for how much weigh this configuration can safely hold.

I am looking at making a small houseboat/floathome powered by a jetski.
i hate conventional designs and am look at options. Possibly using glass, and aluminum filled with solid foam.

Looking at a way to get around how boxy the thing looks....

Thanx

 

Taylor,

Assume you weigh it down to a draft of 18". The load they can hold is:
(36" = 3 ft, right?)

(phi/4)*3'*3'*24'*Sg - "own weight of both pipes"

Sg being specific gravity of water in [kg/cu.ft]

 

a liter's to kg's is easyer Peter i too was looking at the poly or aluminum covered foam panels, see the doodle. seems there rules also...
and for the box: "a sharp rectangular shape can have its drag cut by 80% with a corner radius that is only 20% of the height of the body"

 

Thanx Guys,
The pontoons i have are nicely tappered at the bow.
Now to figure out how much they weigh...

Yipster, I quite like your design...

 

19" Dia. 110.70 LBS. per Foot
22" Dia. 150.60 LBS. per Foot
24" Dia. 180.95 LBS. per Foot
26" Dia. 213.30 LBS. per Foot
27" Dia. 229.00 LBS. per Foot
29" Dia. 267.50 LBS. per Foot
30" Dia. 282.75 LBS. per Foot
33" Dia. 345.00 LBS. per Foot
36" Dia. 407.00 LBS. per Foot
39" Dia. 492.54 LBS. per Foot
46" Dia. 690.00 LBS. per Foot

 

A bare boat with 30" dia pontoons 30' long 12' wide weighs about 1350 lbs.

 

Hi Taylor,
If you're intending to use this as a boat, I highly recommend calling up your local Canadian Coast Guard office ( http://www.ccg-gcc.gc.ca ) for a free copy of publication TP1332 (1999), "Construction Standards for Small Vessels". This includes information on loading and maximum power for most boats, as well as tips on fire prevention, flotation, wiring, etc, and also the forms for getting a capacity plate (which you need to licence or insure the boat). Definitely a worthwhile 5-minute phone call.

 

You have to subtract for the taper. How much depends on the exact shape, but it can be 20-25 percent for one end only, 40-50 percent if both ends are tapered.

 

If you end up foam filling the pontoons/sponsons I assume you add in the weight of the foam into your calculations.

The question remains (for me):
Because there is less room for air in the pontoon/sponson when using foam (as the air trapped in cells is actually providing lift/buoyancy), what factor of loss efficency is there?

Example:
If 10% is a poly-foam cell structure, then the remaining 90% trapped air is what is providing buoyancy, right?

 

No. The pontoon skin is what is providing the bouyancy. It's dimensions and what it displaces is how much bouyancy you have. The foam is just x amount of weight, cargo if you will, deadweight. If the pontoon gets a hole in it and can no longer keep the water out THEN the bouyancy of the foam comes into play . THEN the trapped air is what provides the bouyancy. Sam

 

So you are saying the pontoon/sponsons have two different bouyancy ratings, one non-punctured and one punctured?

That does not make sense, what am I missing to make sense of this?

 

Maybe I didn't understand the question. I'm saying what's inside the pontoon has nothing to do with bouyancy. If you have a 50# chunk of foam or a 50# chunk of lead inside it makes no difference as long as the pontoons are watertight. (A hole above the waterline (or even a topless pontoon) is still watertight) It will float at the same draft because of the 50#, not how big the 50# is. If the pontoon get's a hole and lets water in, the pontoon is no longer providing the bouyancy, but whatever is inside, is. If it's lead, everything sinks as the size of the lead doesn't displace enough water to float itself and the pontoon. If it's foam, everything will float as the size of the foam will displace enough water to float itself plus the (dead)weight of the pontoon. So, yes that is what I am saying, there are two different bouyancy ratings. The unpunctured one is always the same. The punctured one is less, how much so depends on what's inside. Does that help?
Sam

 

Yes, but as said above...it only counts when the skin of the pontoon is punctured. If you add the foam to the pontoon then seal it, it will increase the weight of the pontoon by about 2 lbs/sq.ft. and do absolutely nothing else...up to the time the integrity of the pontoon is compromised. Then you will get a loss of buoyancy equal to the amount of airspace that is available to the water to fill. With a closed cell foam...this will be the airspace between the interior of the skin of the pontoon and the surface of the foam, including any cells that are broken on the surface of the material. The unbroken outer skin of the plastic foam now assumes the duties of being the container. The inside structure only provides support and weight...at 2 lbs/ cu.ft. This is the extent of the loss of buoyancy...assuming that the foam is 100% waterproof. In essence, the pontoon will sink by the weight of the amount of water that can fill the space between the skin of the foam and the skin of the pontoon and come to an equilibrium...in otherwords not much.

Steve

 

No, again. It's not the trapped air in the foam that provides the bouyancy. The size of the piece of foam and the water it displaces is what provides the bouyancy. The trapped air just makes the foam itself lighter. Sam

 

Thank you for the explaination SamSam and lewisboats, it's starting to sink in.