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post #1509 of Old 10-05-2013
Brent Swain
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Re: Pros and cons of steel sailboats

Take a thin piece of metal and twist it. The edges want to be longer than the middle. The middle buckles. When the weld shrinks the edges, it makes things worse. Topside plates , having a longitudinal curve in them, and minimum twist ,benefit from this shrinkage , resulting in a slight compound curve. On my 36 footers ,after final welding you can see about 1 1/4 inch of curve between the sheer and the chine from this effect.
With twisted plates, common on the bow of many hard chine designs ( like Colvins), the distortion of these plates can be difficult to deal with in heavier plate . Far more so in thinner plate. No, a wooden mold wont stop it. Best to minimize the twist in the design stage. Bringing the centreline up closer to the seam is one way to do it.
For seats and floatation, my current dingy uses longitudinal floatation chambers. This not only stiffens things up a lot , but lets me put removable seats anywhere I want them, balancing any other cargo or passengers I may have aboard. It is the best arrangement I have seen in over 40 years of cruising. For aluminium, it takes a bit more fitting , but adds a lot of stiffness, and can be done in 16 gauge, riveted to the top sides, and mostly left open on the bottom, with foam under .
On my aluminium dinghy, I had a midships seat, 16 gauge , 2-90 degree bends a foot apart on top, and 2-90s with 1 inch flanges on the bottom with foam inside, resting on a couple of tabs on the top sides. There is a photo of it on the origamiboats site.
It was nowhere as handy as the longitudinal floatation chambers, with the removable seats.

A man without a project is a man without a life.

This post is aimed at others seeking such info, not at people like Bob, who criticise me for not responding, then criticize me for doing so, when I do .

Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"

Last edited by Brent Swain; 10-05-2013 at 07:29 PM.
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