How to wear my scarf(s)

Discussion in 'Sailboats' started by lewisboats, Oct 1, 2013.

  1. lewisboats
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    lewisboats Obsessed Member

    [​IMG]

    In the above photo I have two scarfs... one each in the oval-esque shapes but should I put the boom's in the box? Instinct(?) tells me there will be less stress where they are than at the extremities but I would like to have my worried brow soothed. I know the mast is a tad (about 8 inches) short but it will have to wait until after Sail Oklahoma next week to fix. This is going on my daughter's EiderDuck to replace the sail and rig borrowed from my Scow (Thunderbird) which you can see in the background.
     
  2. lewisboats
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    lewisboats Obsessed Member

    Oh... I forgot to add that the scarfs are 12:1 epoxy glued and the spars are 1 5/16" fir closet rod. They just barely fit into the sleeves.
     
  3. DCockey
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    DCockey Senior Member

    Bending moment will be greatest where the yards cross the mast, and will go to zero at the ends of the yards.
     
  4. PAR
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    PAR Yacht Designer/Builder

    You're good to go Steve, have fun, unless it breaks, in which case I'm going to suggest it was David's fault :).
     
  5. messabout
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    messabout Senior Member

    Steve, you have been a boatbuilding madman for some time now. I figure that you know what you are doing and your 12/1 scarphs are well done and plenty adequate.

    If you want to get overtechnical, then I suspect that the scarphs will be stronger in shear than in peel mode. That simply means that the joint will arranged so that it is parallel to the sail surface. Fugedaboutit. Probably does not matter in this case.

    I suspect that the closet rod at one and fifteen sixteenth diameter is too big. A really good lateen uses spar bend to shape the sail appropriate to wind strength. If it blows hard you adjust the spar bend to flatten the sail or relax bend to get some fullness. Of course that deprends on the built in curve of the luff and foot of the sail. If your sleeve luff appears to be a straight line then don't concern yourself about the spar bend.

    The picture suggests that you may have the gooseneck excessively far aft on the boom. Here are typical locations for the worlds most famous lateen rigged boat. Of course I am referring to the Sunfish. The luff and foot are both 160". The leech is about 175 inches. The yard is typically attached to the mast head somewhere between 110 to 125 inches above the tack. The gooseneck is positioned from 17 to 20 inches aft of the tack. You could fiddle with the proportions to see where your sail falls within this regime............Or you could just say "to hell with it" and go sail the boat without worrying about all that techical stuff.
     
  6. lewisboats
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    lewisboats Obsessed Member

    Actually I don't have much say in the matter of where things fall (I kind of wish I did)... there are cutouts in the sleeves for all the important stuff. There is maybe 4-5" of leeway in the cutouts but that is it, and the mast takes up close to 3 of those inches. There is a cutout where the yard crosses the mast to hook up the halyard, another where the gooseneck (actually a ring attached to an eyehook in the boom on the original) and another for attaching the main sheet about 4.5 ft aft of the mast. The closet rod is one and five sixteenths and plenty bendy... I fear maybe a bit too much but we'll see. I plan on bringing the backup rig as... well... a backup, just in case the plan doesn't "come together".
     
  7. hoytedow
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    hoytedow Wood Butcher

    Thanks, messabout, regarding scarf/strain alignment. That is something I had not considered and it may prove useful to me to know.

    Steve, maybe some slight tapering of the closet rod will help it flex appropriately, flexing where you want it to bend, when under sail.
     
  8. hoytedow
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    hoytedow Wood Butcher

    A line of lightweight fiberglass tape along the forward edge of the rod will stiffen it, making it flex less where you want it to stay straighter. Of course, when you tack, that may be counter-productive.
     

  9. messabout
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    messabout Senior Member

    Steve; I reckon that the sleeve cutouts pretty much dictate how you can erect the rig if you choose to leave them as is. You might have to fiddle the mast location such that it will be happy with the boat and visa versa.. Lee helm...bad scene, weather helm....safer if not too much. When you splash the boat you will know which is what.

    Of course you could make use of the hot knife wherever on the sleeve that you might want to attach something. If the boom is intended to be sheeted from the clew end, you can make some cuts in the sleeve so that you can lead the sheet through a block nearer mid boom The sheet would tie to the traveler somewhere near end boom and then led forward to the mid boom block, and then down to hand. That will take some of the diagonal bend out of the boom. The yard will still bend a'plenty if you vang the boom hard enough.

    The sleeve luff is a perfectly good way to attach the sail to spars. Whacking up the sleeve is not a disaster if you consider that laced or tied on sails have grommets every ten or twelve inches and that attachment method works just fine.

    Good luck and keep on Keeping on.
     
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