Sunday, February 11, 2007

Inwales a.k.a. Sheer Clamps

In the Jimmy Skiff ™ building instruction book which accompanied the plans, the solid wood strips that run along the inside of the top of both sides of the boat hull are referred to as 'sheer clamps'. Since the side of the hull is the 'sheer', and the wood strips serve to help hold the shape of the sheer, I can see how this term would be descriptive, especially when a deck is attached to the top of the sheer clamp. More frequently, I have seen these parts referred to as 'inwales', when discussing an open hull. According to a wikipedia article, "The gunwale, pronounced 'gunnel' to rhyme with 'tunnel', is a nautical term describing the top edge of the side of a boat." The gunwale typically consists of the inwale on the inside, and the outwale or rub rail on the outside of the hull.

Since the temperature climbed up out of the single digits to about 30° here yesterday, I decided that it was time to once again crank up my tiny portable electric space heater and resume work on the Jimmy Skiff ™ project. My workshop is insulated pretty well, so I just use the portable unit. It will hold the temperature in the shop at about 70°, even when it is very cold outside, but when it is less than 25°, the heater has to run constantly to maintain the shop temperature at a level warm enough for curing the epoxy. Since my shop has been unheated for a couple of weeks, it took all day for the temperature to rise to 70°. Not only does the air need to be heated, it is even more important that the wood and epoxy are warm before attempting to glue or saturate with epoxy.

After the scarf joints on the inwale pieces have cured, the next thing to do is to cut the inwales to length. Since there will be a deck over the bow which will hide the miter joint where the two sides meet at the stem, I started by cutting the stern end so that I would get as near perfect fit as possible where it would show. This is a compound angle cut because the sheers and stern are angled out toward the top. I left the inwale slightly proud of the hull, and I will trim it flush after the epoxy cures. When using 'c'clamps, it is a good idea to protect the wood with a small piece of scrap material.

After I fit the stern ends, I marked and mitered the ends where they meet at the stem. Again, these where compound miter cuts due to the flare of the sheers. Since the deck will have a bit of camber, leaving the inwales slightly raised will allow me to trim them with an angle that will match the underside of the deck for a nice tight fit.

Since I needed a clamp about every six inches, I used every clamp I had in the shop, except for the long bar and pipe clamps.

I didn't have quite enough clamps, and I am going to be adding rub rails or outwales later, so I used 1" drywall screws to temporarily hold things snug in a few spots. I drilled pilot holes before driving the screws. I will remove these screws at the same time as I remove the clamps.

Next I will add the bulkheads and seats. I will leave the top off the rear seat until after I turn the hull over again to add the skeg. This is because the skeg is screwed on from the inside and the rear seat top would be in the way.

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