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Old 01-02-2014
Brent Swain Brent Swain is online now
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Re: Pros and cons of steel sailboats

Quote:
Originally Posted by outbound View Post
Disclaimer- although I briefly went to engineering school I have no detailed knowledge of N.A. or structural engineering and unlike some admit it.
Still seem to recall all metals have thermal expansion and contraction issues. Although of greater degree in Al still operative in Fe. This is one reason framing in metal boats allowed to " float". Also seem to recall allowance for thermal effects is incorporated into design of attached framing such as at watertight bulkheads.
Seem to recall metal around welds and welds asked to handle load cycles generated by thermal effects are more likely to fail.
Also recall t or angle framing cut and welded to allow curve is much stronger than simple framing bent to curve.
Wonder how above issues impact on Brent boats.
I asked my 91 year old father, a steam engineer most of his adult life , how much a hot exhaust pipe will expand when heated . He said " At 1500 degrees , a quarter inch in 15 feet."
It is not an issue on finished boats , but weld shrinkage while building is. That is why the roughest framed boats are those in which all plating was first attached to frames before doing the long seam welding, and the fairest are those in which the longitudinals are left to float free from the frames while the long welds are done, and only attached to the frames after the welding is done. Shrinkage from chine welds will lift the plate off the frames, sometimes by over an inch, in a beautiful ,slightly compound curve, if you let it.
If the plate is first welded to the frames, it cant move ,the edges shrink anyway and you get an oil canned , hungry horse look.
Welding the plate to longitudinals before final welding of long seams has no negative effect on distortion, but helps avoid distortion.
With frameless, the plate is free to move, and welding is far more forgiving. More shrinkage simply means more beautifully fair, compound curve. I have seen an inch and a quarter of compound curve between the chine and the sheer.
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Brent Swain, Boat designer, Builder, and author of "Origami Metal Boatbuilding"