# How much can a pontoon carry

Discussion in 'Metal Boat Building' started by Wemdoug, Jun 1, 2010.

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### WemdougJunior Member

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

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### alan whiteSenior Member

Calculate the volume of the pontoon in cubic feet and multiply by 31 lbs. That puts the pontoon halfway submerged.

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### WemdougJunior Member

Thanks alan white but sorry please why multiply with 31lbs

4. ### apex1Guest

because one cubicfoot has a buoyancy of roughly 62 pounds. Half of the hull is not submerged, therefore it lifts nothing.

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### IkeSenior Member

Freshwater weighs about 62 pounds per cubic foot of water. so to find how much your pontoon (or any boat for that matter) will suppport, you calculate the volume of the submerged portion. In the case of a pontoon you only want half of it submerged. You would take that volume and multiply it by 62. But alan took the short cut. He calulated the full volume of the pontoon and multiplied by 31. the result is the same. Remember you have two or three logs here. So you you multiply by two or three depending on how many pontoons there are.

But that is the maximum weight capacity, which is far more than you should ever pout on the boat. You have to subtract engine weights and gear weight to get persons capacity in lbs. persons capacity in pounds + 32 divided by 141 is the number of people. (or you can do a rough estimate by dividing persons capacity in pounds by 165)

If you want to see the standard for it, it's on Canada's web site (it's the same in the USA) at http://www.tc.gc.ca/publications/en/tp1332/pdf/hr/tp1332e.pdf. Go to section 4.5 on page 48 of the pdf, Recommended Maximum Safety Limits for Pontoon Vessels. This is taken directly from the American Boat and Yacht Council Standard for Pontoon boats.

Last edited: Jun 1, 2010
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### WemdougJunior Member

Thanks ike your great but more sugestions cos i need to know all there is to know

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### IkeSenior Member

If I knew all there was to know I'd be a wealthy man. I'm sure there are folks on here that know a lot more about pontoon boats than I do.

8. ### Submarine TomPrevious Member

Most importantly use your total weight.

Fuel, dock lines, coffee cups, everything, and then add 20 % as a safety factor.

Don't forget the weight of your pontoons!

-Tom

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### GTS225Junior Member

FNG here. Found this thread, and thought I would clarify the process with my own numbers. Will start a seperate thread explaining what my idea is.

OK.....so if I have a single steel tank, 53" tall, 16" dia, that calculates out;
53" = 4.41'
16" =1.33'D, or .665'R
Pi*r squared= .665*.665=.442:.... .442*3.14159=1.38:.... 1.38*4.41=6.08
6.08*31=188, so one of these tanks would support 188# at half submersion.
(I didn't round up with these figures. Figured it would give a small safety margin.))
If I weld three of them together lengthwise, I get 564# of floatation, minus the weight of the tank assembly, right?
This would give me a single pontoon 13.25' in length. Add a second pontoon, I get 1128# of support, (minus weight of pontoons), that I can build a little lake (or gentle river) boat on.
I would also get compartmentalized pontoons, so that if one compartment was breached, the other two would provide support, but the platform would list.
Are my calculations and conclusions correct?

Thanks.....Roger

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### PARYacht Designer/Builder

Wemdoug, if you want someone to do the math for you, or explain the very simple mathematics involved, then you're in way over your head, as far as "designing a passenger carrying" boat. There are hundreds of calculations and computations necessary in the design of even the most simple of vessels. A vessel that carries passengers needs to adhere to very specific and required guidelines and requirements, set down by the governing bodies in your country. If you have no governing bodies in your country, then this is more reason to adopt these requirements.

We read much too often, about poorly designed and skippered vessels in countries like this, where many people die as a result of very unqualified people, attempting to do exactly what you are. The ship design and engineering skills necessary aren't going to be found asking for answers, to extremely simple mathematics questions on line. You need an education in both.

Simply put, a commercial vessel's plans can be had from any reputable designer, for not a lot of money. Sizes range from 18' (7m) and up. I have a 54 passenger semi displacement vessel, designed for 3rd world construction with limited boat building experience. It'll pass any EU or US standard you list and it's fairly cheap to build and maintain. The plans cost \$2,500, which is a steal considering what you get. You'll find stock plans from most of the designers in the world, prices ranging of course, but the hydrodynamic and engineering issues are solved (no math) and you will not drown anyone the first time out either. I strongly urge you to buy a set of plans. The cheapest plan set I sell for a commercial craft is a 24' (8 m), fishing boat, which could be easily converted to passengers for hire. The plans cost \$500 (USD) and again this is a real bargain, especially compared to drowning in mid river.

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### WemdougJunior Member

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### vaporvetteJunior Member

That won't make a good pirate boat at all.

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### IkeSenior Member

I gave you the reference for pontoon boat capacity. It can also be found on my web site at http://newboatbuilders.com/pages/pontoons.html. You will have to do the math.

Keep in mind a cylindrical pontoon should be loaded only to half it's capacity. As the waterline moves upward, capacity increases. But once it reaches midway the capacity starts to increase less rapidly. you need some reserve buoyancy, so load it only to the middle of the cylinder. In other words only half it's actual load capacity.

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### gonzoSenior Member

Wemdoug: Par went about it by spending many years studying, working with experienced people, building and repairing boats. A few responses on the forum are not enough. If it is true that you don't give up so easily, then congratulations. You may end up joining a group of people that have spent many years of effort, and often making little money out of it, to gain expertise.

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### PARYacht Designer/Builder

Wemdoug, don't give up, but understand this, you'll need to have a a very solid understanding of structural engineering and yacht design, which are two different disciplines. You can take an on line course such as WestLawn, which will greatly help your efforts, in this and other boat design projects, but it'll cost a lot more then just buying a set of plans. I think a basic WestLawn course will cost about \$2,500 (USD). You should be able to get stock plans much cheaper then this. It's your choice, but judging by the type of questions you're asking, you'll need at least freshmen collage level mathematics understanding, which you currently don't have (not even close in fact), so some preparatory courses may be necessary, just to "tune up" for the yacht design courses. I say go for it, because your country needs many more skilled yacht designers.

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