how to calculate adding pontoons to a 12FT aluminum V bottom boat

If you are doing outriggers, then do not plane the boat. At those speeds, catching a pontoon on an outrigger can either rip it off, or twist the boat hard enough that occupants go flying.

If you want to keep the boat stable, then the pontoons have to be IN the water, not above the surface. They don't have to be submerged, but should be reasonably close to their maximum cross section.

There used to be a brand of canoes that had 4" foam floats just under the gunwale. Useless of course, and they didn't give any floation until the gunwale was 4 inches from the water. (Worse than useless: They moved the shaft of the paddle 4 inches further from the centerline, decreasing paddling efficiency nd increasing the torque turning the canoe)

A v-bottom hull tends to have low primary stability, but great secondary stability. A flat bottom hull the opposite.

It's easy to tip the boat some, but as you tip it, the part in the water becomes less like a log and more like a plank, so stability increases.

Good canoes are shallow v bottoms. It makes it easy to lean the canoe to get higher performance turns. Also makes the bottom more rigid with less material making the canoe lighter.

The problem with v-hulls is why triple v hulls are popular.

Edit added after question revision.

Caveat: I have zero experience with Starcraft. We have a lot of Lund aluminum boats that sound similar. They strap nicely on the support struts of a Cessna 180 (a.k.a. Far North Pickup Truck) The most common size is 12 feet long by around 4.5 feet wide. Everyone uses them with 9.9 hp Evinrudes. (You don't need a license for a boat under 10 h.p.)

My experience with these boats is that they are virtually un-tipable. I've certainly seen many people standing in them casting. In fly in fish camps,the usual use is 1 guide, and two fishermen. I have never seen one with pontoons.

Ok. You want pontoons. I would suggest that you build the pontoons as a frame that is then attached to the boat. There are several options for storing the pontoons.

A: The pontoons telescope out. The main frame is a pair of tubes, the pontoons are on tubes that slide inside. I think this would be reasonable to do with schedule 80 2.5" PVC pipe. When not in use, the pontoons hug the gunwale.

If the pontoons on both sides share the same tube, the maximum extension is about half the width of the boat. Note however my earlier comments about them needing to be in the water. This makes the tubes run at a slant. The interior ends of these tubes are going to be a PITA.

B: The pontoons are hinged, and lock vertically when not in use. Not sure how to best make a locking hinge.

In this position they will catch the wind, but probably not a big deal. They will make getting in and out of the boat sideways on a dock difficult.

C: Like B the pontoons are hinged, but flip all the way over and rest on the opposite gunwale when not in use. This makes the pontoons in use a very wide platform.

posted over 6 years ago

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Sherwood Botsford‭

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