Need help with load calculation

Hi all
I am trying to figure out my load capacity for an old pontoon boat I am refurbishing, The boat is a 1970 Kayot 22 foot. The pontoons are steel and measure 19" diameter with 20' of round tube and 3' of cone. I can do the calculations for the buoyancy but what I don't know is the weight of the tubes.
Thanks for the help.

 

Welcome to the forum.
If the pontoon is afloat, take the drafts fore, aft, and in the middle, which will allow you to know the total weight at this time. Perhaps starting from that figure it will be more comfortable for you to deduct the weights to be eliminated and add the weights to add.

 

Hi Paul - are you sure that your pontoon boat is built with steel, rather than aluminium?

If she is indeed steel, and she was built in 1970, I would be a bit worried about the shell thickness of the pontoons.
Is there any rust visible anywhere?

If she is aluminium, is she similar to this one?
2002 Harris Kayot CLASSIC 220 in Rapid City, MI https://www.smartmarineguide.com/L51194030

Re calculating the weight of the tubes, you can get a rough estimate by 'unrolling' the tube to create a flat surface.
For a 19" diameter tube, the circumference will be 3.142 x 19 = 60" / 5'.
The surface area of the plate in the 20' section of tube will be (5 x 20) = 100 square feet.
Multiply this by the thickness of the steel plate to get the volume of the material.
And then multiply by the density of the material to get the weight of the 20' length of tube.

 

@ TANSL The boat is out of the water and came to me with a deck only, which I have removed.
@ bajansailor The tubes are definitely steel and in really good shape. No rust on outside and the inside looked good as far as my scope would go.

 

I am intrigued by how your 50 year old steel pontoons are in such good condition, even on the inside - do you know what sort of paint coating has been applied to them? And is there any paint on the shell inside the pontoons?

 

The inside may have had oil in them at one time as I am still getting a little residue out. The outside looks to have at least three distinguishable coats of paint and the bottom of the tubes are coated in coal tar.

 

Are there float marks on the pontoons?
You may have no choice but to use a crane to weigh it.

 

The load capacity for pontoon boats is based on the 1/2 the volume of the pontoons. see this page for how to calculate the weight capacity. It's fairly simple, no high level math involved. Boat Building Standards | Pontoon Boats | Capacity Horsepower Flotation https://newboatbuilders.com/pages/pontoons.html

I realize it's in metric, but after you find the weight in Kilograms just multiply by 2.2
(1 Kilogram = 2.2 lb)

 

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