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Dan McCosh
05-09-2003, 03:33 PM
I'm scarfing a section of a mast, and plan to use a "clothespin scarf" joint. The cross section is rectangular, with the deep part fore and aft. Question is which way is best for the scarf to run? Laying it out so the "V"is visible from the side seems the best--easier to cut and seems the strongest. Any opinions?

Ian McColgin
05-09-2003, 03:51 PM
I was eyeballing and I'm not sure there's a lot of difference in glued surface area either way. I suspect it would be easier to get a great fit if the V were visible from the sides as that way through most of the structure you're actually matching normal surfaces, but aesthetically it's nicer to have the V on the fore and aft parts so it's not so visible.

G'luck

Dan McCosh
05-09-2003, 04:16 PM
I think the gluing area is the same, but the length is longer when the "v" is on the side--this seem to me to add something to the overall strength, as much as I can figure out the stresses on a mast. (The joint is just above the deck.)

Bayboat
05-10-2003, 12:25 AM
Dan, you and Ian are right about the positioning of the scarf. Maybe a forumite with an engineering bent can corroborate my intuitive persuasion that having the long, down-pointing parts of the scarf on the fore and after sides of the mast is stronger. Anyway, that's the way the "Old-timers" did it. Since the scarf is near the deck I assume that it will be in a solid section. You can scarf the planks and lay a solid piece inside, extending down through the partners to the heel and a foot or so from the top end of the scarf. There is a fancy four-part scarf for masts that was developed by Phil Rhodes to distribute the stresses gradually, but I don't think you have to do that since the scarf will be down near the partners. At least 1:12, more if you have plenty of wood. I would use resorcinol or Weldwood if it's varnished; epoxy is OK if it's painted.

Nicholas Carey
05-10-2003, 01:32 AM
Originally posted by Bayboat:
Maybe a forumite with an engineering bent can corroborate my intuitive persuasion that having the long, down-pointing parts of the scarf on the fore and after sides of the mast is stronger.The scarf orientation shouldn't be an issue. For starters, the glue join should be stronger than the wood itself.

Second—assuming that it's a stayed mast—the mast is a pure compression member. So sayeth the riggin gods anyway.

George Roberts
05-10-2003, 11:41 AM
according to the APA:

8:1 (or more) scarf joints will carry 100% of the allowable stress in tension or flexure.

5:1 scarf joints will carry 75% of the allowable stress in tension or flexure.