Posted by: oldsalt1942 | May 3, 2015

Learning Curve

I’ve decided that I should build a pontoon-type boat, doing it in four-foot segments (possibly eight-foot if I can be sure to divide that in half with a leak-proof bulkhead. These segments would be built here at the house in Boquerón and then trucked down to the marina in Pedregal where they’d be bolted and epoxied together. I have a LOT of experience with thickened epoxy as a bonding agent and I KNOW that the wood around the epoxied joint will give way before the joint will.

The pontoons will be 2-feet wide by 2-feet high, and between 24 and 28 feet long. Probably the latter. The beam of the boat will be 10-feet, with the house being 8-feet wide allowing for a nice roof overhang, or whatever that’s called in carpentry terms.

I decided on the pontoons because of the amount of flotation they offer. Here are the numbers I’ve come up with…

Each pontoon segment will be 2’X2’X4’ = 16 cubic feet

One cubic foot = 7.5 gallons (7.48)

One gallon of water weighs = 8.3453 pounds. One cubic foot = 7.48052 gallons. The weight of one cubic foot of water is 7.48052 gallons times 8.3453 pounds, which equals 62.42 pounds of water per cubic foot. OR, it would take 62.42 lbs. to completely sink a cubic foot container.

SO, 62.42 lbs X 16 cubic feet = 998.72 lbs. displacement for each 4’ pontoon. Minus the weight of the materials each pontoon will support, roughly, 900 lbs.

The sections in the bow would be made like the bow of a barge or scow, sloped up from the bottom to move through the water with less resistance. Figure that each one of those will be roughly half the volume of the regular one for a 28’ long structure overall, or roughly 11,700 lbs. flotation. Whatever kind of house structure I build on top of the pontoon segments plus all the junk that I’d bring aboard certainly isn’t going to amount to five and a half TONS!

If you look as building a raft-type structure using 55-gallon drums the figures look like this:

Now, a 55 gallon drum measures 35” X 24”. A 55 gallon drum will displace 459 lbs.

Because of the odd measurement of 35” you’d need 10 drums to make up each pontoon of a similar size to the plywood pontoons. Now you’re mucking around with non-standard size lumber or going for 10 barrels a side. The cheapest 55-gallon plastic barrels I’ve found around here cost $30/each (can’t find a source for used barrels like in the States because if they are available they’re snapped up instantly by people who use them for water storage.). That’s $600 for flotation. And how much flotation? Potentially 9,180 lbs., before deducting the weight of the materials needed to contain them. So more than a ton less flotation than the plywood pontoons.

I tried drawing these pontoon segments out on paper, but it wasn’t very successful, everything in 2-D. So I downloaded the free SketchUp design program and found out there’s a HUGE, STEEP learning curve and the frustration level was almost more than I could bear.

So, one Sunday morning last month I went into David (Dah VEED) to the store where I knew I could get 2′ X 2′ X 4′ styrofoam drop ceiling tiles, 1/2″ thick which is EXACTLY what like a pontoon segment would be like. (I’ve since decided that the bottoms of each segment should be 3/4″ thick instead of 1/2″. Using a hot-glue gun to assemble the pieces (Elmer’s School Glue took too long to dry and needed constant pressure to stick together, and contact cement INSTANTLY melts styrofoam) this is what I came up with.

IMG_0729

IMG_0730

IMG_0731

Not only did this help me to visualize the building process, I found out that certain things had to be inset from an edge to accommodate other pieces.

If there’s one character trait I possess it’s that I’m STUBBORN! I became bound and determined that I was going to learn how to use the SketchUp program at least well enough so that I could document here, and possibly later in e-book form, how to build this boat. So I watched, over and over again, various YouTube tutorials on how the program works. I had to constantly trying something, discarding it, repeat, repeat, repeat. But I persevered and, while the measurements are a bit off at least I was finally able to get something resembling a 3-D rendition of a pontoon segment…

Segment 1Segment 3

Those end pieces that stick up above the pontoons are where the 2 X 6 cross beams will attach the pontoons to form a catamaran structure. End to end each 4′ section will have a one-inch-thick attachment point. Bolted and epoxied they should be strong enough to be able to move the boat without a problem. So, diddling around some more with SketchUp, and getting better at it all the time though still having to try something, discard it and do it over again, I came up with these ideas.

28-foot pontoon 2

This is what a pontoon would look like. That square thing in the bow would be a hatch so I could use those segments to store anchor line and fenders.

Here they are with the cross braces and decking…

28-foot pontoon with cross braces28-foot pontoon with decking

So that’s what I’ve come up with so far…

 

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