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PostPosted: Mon May 22, 2017 2:17 pm 
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Joined: Tue Oct 22, 2013 10:38 am
Posts: 25
When I first assembled my Aleut, I was disappointed to find that, after inflating the sponsons, there were wrinkles along the gunwale in the canvas fabric at the bow and stern. I noticed (from web photos) that newer models did not seem to exhibit this tendency. Older models however, seemed to be plagued with bow and stern wrinkles, some more than others.

The sponsons that I had were the older (clear vinyl?) type. I ordered two new sponsons (the urethane coated nylon? type). When I pressurized the new sponsons, they did, indeed remove some of the wrinkles, but they wouldn’t hold the pressure more than a few hours. There was no air leaking around the tubing or valves. The fabric itself was porous. When inflated and held submerged for a day or so, small bubbles could be seen forming on the exterior of the fabric.

I bought some Inflatable Boat Sealant from West Marine, a very thin latex sealant that you put inside inflatable boat tubes and slosh around. Not cheap, about $65 for a bottle. I put a coat inside the new sponsons, let it dry, and voila, the sponsons would hold pressure for a month or more. I had enough sealant left over to do about 3 more sets of sponsons. Want some?

The new sponsons solved some of the wrinkle problem, but some of the wrinkles were still there, especially at the bow and stern. They bugged me.

I decided to try fitting some pipe insulating sleeves over the ¾ inch aluminum tubing along the gunwales. First I tried some polyethylene foam. These worked okay at first, but took on a compression set after a while. I replaced them with a rubber foam by Frost King, which retained its’ shape much better, but still showed compression set. I removed all of the insulating sleeves.

I believe that the problem with the wrinkles is due to the type of sponson (vinyl vs. nylon) and position of the sponson pocket along the gunwale. This seems to have been addressed by Folbot in later models, as the position of the sponson pocket appears to have been moved up, and photos of the newer models don’t show any wrinkles. When the sponson pocket is more or less centered over the gunwale tubing, the tubing divides the sponson in half, and each half inflates to lift the hull fabric off of the tubing, thereby tightening the hull and removing the wrinkles. The sponson pockets on my hull are stitched with the seam just inboard of the gunwale tubing. I didn’t want to move the sponson pockets.

Then one day it kinda hit me; don’t know why it took so long. If the sponsons are just hanging below the tubing, which they were, there is nothing for them to press against as they are inflated, so they really couldn’t push the wrinkles out effectively. I cut some pieces of 1/8” luan plywood (exterior glue) and temporarily taped them to the side frames on the bow, between the tubing and the skin. When I fully inflated the sponsons, my wrinkles almost entirely disappeared.

I then made my plywood panels for the bow and stern. The grain runs vertical. They sit flush with the outside of the tubing and have wooden strips that prevent them from shifting up and down on the tubing. They are taped to the tubing with two layers of glass-reinforced Pro 182 tape that is rated to 200 degrees F, 100 lbs. tensile strength. The panels were given one coat of West epoxy, sanded, then painted. The panels are 21” long. A set of 4 weighs about 10 ounces.

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