How much can a pontoon carry

[Poida]

I noticed noone mentioned balance. I do not think, in my basic brain, that adding up all of the weights and calculating the displacement by calculating the volume of the pontoons is enough.

You may have to much weight, ie the engine at the stern and if weight distribution is not taken into consideration, the pontoon could float on a 45deg angle.

[Ike]

You are right, but I think a stability calculation is a bit beyond what you you have learned so far. At this point just try to keep it balanced so it floats level fore and aft and side to side. Adding up all the weights can assist with that. When you add them up, note where they are. You should have as much weight on the port side as on the starboard, and weight should be evenly distributed fore and aft. Pay particular attention to where the weights are vertically. Try to keep weight as low as possible. Avoid weights up high.

[Wemdoug]

nice. thought of that so i decided to introduce four ballast tanks in strategic points to level out any tilt.

[PAR]

Yea, that's the way to handle it . . .

[koolly]

Hi everyone,
Learned a lot just reading this post and website. I have a 33' houseboat I bought and wanted to renovate it some but like to know what the max weight would be. On the ownership it has a registered tonnage of 5.44, not sure if that weight it can carry, weight of the boat or even just a guess the boat maker made.
Here is the specs and pictures of boat if anyone can help that would be great.
Registered tonnage; 5.44 tons
Boat size: 33' x 10' ( 33.5 x 11.5 with pontoons)
Steel Pontoons 33.5' ( 24'' W x 22'' H )

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[Ike]

The maximum weight capacity of a pontoon boat is 1/2 the volume of the pontoons times 62.4 lbs/cubic foot. To determine the maximum weight capacity measure one pontoon and calculate the volume of the pontoon (I'm talking in feet and cubic feet). Multiply that by 62.4 lbs/cubic foot, which is the weight of fresh water per cubic foot.

Take your boat to a truck scale and weigh the whole thing. Subtract the weight of the trailer. That gives you the boat weight. Subtract that weight from the weight in the calculation above. That's how much weight you can carry. I would use a safety factor and divide that by two. Divide that by 165 (actually the Coast Guard is now using 180 for commercial passenger vessels, but not for recreational boats) to get the number of people. There is no specific USCG formula for number of passengers on a recreational boat this size.

There are more sophisticated ways to measure this but the above should put you in the ball park.

[PAR]

Poida, getting a boat to "trim" properly on her DWL is the reason you preform the weight calculations. It's all very simple math, though tedious if preformed by hand. With the weights study in hand you can calculate where she'll sit, relative to her DWL and make adjustments to her MT1 to get the fore and aft relationship correct. Without the weight study, you are correct and you'll have no idea where she'll float, let alone what her trim might be (bow up or down, etc.). In fact, these simple calculations are one of the very first things you preform in the design process. Nothing looks worse then a freshly designed yacht, getting splashed for the first time and she's several inches down at the bow or stern, maybe even the boot stripe completely under the water. Every launch I've attended, this is what I sweat over. Did I miss something, did I get all the centers right, did the builder move something, can some trimming ballast fix it. With some luck, she'll float a little high and level or nearly so. This way you can just move a fuel tank a foot or maybe shift some trimming ballast a tad and she's right where she's supposed to be. The only way to know how much to move or add or subtract is with the MT1 number in hand.

[TANSL]

Originally Posted by Wemdoug

Hello Everyone
Please can any one help tell me how to calculate how much load a pontoon can carry. Cos i am designing a simple passenger carrier and i intend to place the deck directly on two pontoons.
Thanks
wemdoug

In addition to calculating barge draft you need to achieve the desired displacement and carry the total load you want, it is very important to find out if the main deck will have sufficient strength to withstand these loads. Another important issue is the torsional moment at which the subject will be covered.
You are dealing with a structure, two pontoons and a deck, with some connection problems to be studied carefully.