Splicing in a new masthead

Discussion in 'Sailboats' started by kreitz, Sep 18, 2006.

  1. kreitz
    Joined: Sep 2006
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    kreitz New Member

    Folks,

    I am currently repairing a masthead that has deteriorated around the masthead fittings. After removing the fittings and rotten wood there is not much left ('cept some epoxy from a previous repair attempt by previous owner).

    I am not sure what the forces on a masthead are -- presumably mostly downward -- so i am not sure what type of joint would work best.

    I believe the mast is douglas fir -- unavailable around these parts -- and so I must use another wood. Any Ideas...?

    Southern yellow pine and ash have similar qualities...

    cheers for replys
    Reitz
     
  2. bntii
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    bntii Senior Member

    You might try reposting this in the wooden boat forum for some really good advice. I can offer how I would proceed:

    A reasonable splice for a new masthead is formed like an old fashion clothes pin. Think of one of those old wooden clothes pins set over a dowel rod and you get the ideal. The top of the mast is tapered to a blunt(1") point with a bevel on each side. The new mast head is cut with a deep V in the base which corresponds to the tapers you have cut. Glue up w/resorcinol, varnish and away you go.
     
  3. PAR
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    PAR Yacht Designer/Builder

    If it's a solid mast then just use a 10:1 or longer scarf joint and glue in a scab to good wood. The joint should face fore and aft. Don't use epoxy on a solid mast, because the dimensions of the spar will be too big for the glue line to withstand expansion and contraction with moisture content. Yellow pine would work, ash doesn't have the rot resistance qualities necessary for marine use, without careful attention and finishing maintenance.

    A box section or other type of hollow mast will be repaired differently, though the scarf joint (8:1 or better) will serve well here too. Because of the built up nature in a hollow mast, the stave joints need to be staggered. 8 times the thickness of the mast (minimum) vertically, so that no two joints. This means a larger amount of good lumber will need to be replaced, but this is the cost of this type of repair. Home Depot and Lowe's sell Douglas fir decking stock in 1" x 6" or 5/4" x 6". Pick out the nicest, straightest tight grained, quarter sawn piece you can. You may have to go through several stacks of lumber to find a good one. You'll note some are much heavier then others, set these aside, as these will be the ones you'll be selecting from.

    Plastic resin, epoxy or resorcinol will work fine on a hollow mast.
     
  4. kreitz
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    kreitz New Member

    Thanks for the replys ...

    I posted this in teh design forum because I think there are engineering concerns involved and I am interested in the forces applied at the masthead -- this in turn will give me some insight into why a certain scarf or other method of repair is better than another...

    What are the forces acting on a masthead ... a friend suggested that the force would be mainly compression (downward) so a simple well seated mortice and tenon joint would be sufficient. I am dubious. There must also be some fore/aft and sideways bending action going on. I am not at all sure what the forces on the top 12" of a mast under sail would be ....

    here we are looking at a rather short eliptical spar (26') that appears to be cut in half longitudinally and hollowed out up to the masthead sheaves. Halyards are internal ... the masthead from the tip to the sheaves (about 8") is not hollowed out and is tapers to slightly larger than a 2x4. Unfortunately the rot extends to about an inch above the sheaves so a scarf would straddle the hollowed out section and the solid section -- complicating the woodwork.

    I rather like the idea of internal halyards for their tidyness quality but may, for simplicity's sake just scarf in a new masthead, plug the sheave holes and run the halyards outside the mast ... alas.

    Cheers,
    Kurt
     
  5. PAR
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    PAR Yacht Designer/Builder

    The loading can get a bit complicated, but it is mostly compression for your needs.

    The mast was likely built as halves and had a plug inserted at both ends (typical construction). The internal halyards can stay and the scarf can be made full length, then split, per the original arrangement. You'll cut out the sheave pockets after the scarf work and halving is completed. You may have to hollow out the back to accommodate the halyards, but that's not so tough. The sheave pocket makes the scarf a better choice then a mortise. Hard corners inside joints can make stress risers and trap moisture if the joint isn't perfect, a scarf will drain away any moisture and transfers all compression loading.
     
  6. hallaquila
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    hallaquila New Member

    wooden mast repair

    bntii: I know this is an old post, but you seem to know wooden mast repair. I just discovered a problem with my composite box sita spruce mast this evening and I didn't want to wait until tomorrow to track down a wooden mast master in Annapolis. I have a tall rig--overall 47 feet, keel-stepped with lower spreaders and a upper jumper stay. I over-tensioned the backstay to correct a topmast forward cant and cracked the mast below the jumper stay shroads and below where the inner jib shroad connects forward. It is a bad crack that buldged the sailtrack. I restored a 1951 custom steel yawl which was out of the water for 20 years and rebuilt with a ships carpenter both masts using West System. There was no rot decernable six years ago. My question to you is it possible to repair a break like this? Is it cost efficient compared to a aluminum replacement? Anyway, just a shot in the dark. Thanks,
    Tom Hall
    Baltimore
    hallaquila@yahoo.com







     
  7. alan white
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    alan white Senior Member

    If the mast is a box section, forget the clothes pin repair, which is for solid masts only. PAR described the proper repair method (see the first of his comments this page).
    A good boat carpenter can reproduce the upper section a lot cheaper than the cost of an aluminum replacement, I'm sure. If the rest of the mast is sound, save it, unless you've been waiting for a reason to change to an aluminum stick anyway.
     
  8. PAR
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    PAR Yacht Designer/Builder

    Alan beat me to it. Epoxy does work on "assembled" masts (like yours). Aluminum has been coming down in price in recent months, but is still quite high. Any reasonably experienced boat carpenter can cobble together a fair repair for your stick.
     
  9. Brent Swain
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    Brent Swain Member

    I've always used a 12 to 1 scrarf. You can make a jig by nailing a couple of 2x4s to the sides of a plank wide enough to accomodate the mast, at the 12 to 1 ratio, sighting accross them to make sure they are in line. Then push your router thru a hole in a piece of 3/4 inc plywood. Then , after clampin the mast section or the add on onto this jig, you slide the plywood with the router screwed down to it ,up and down the 2x4 runners , gradually lowering the router until you have machined a smooth surface. Then do the same to the other piece and the two machined surfaces will match up perfectly. You may have to drive a nail thru them to stop them from sliding while you glue and clamp them together.
    Brent
     
  10. alan white
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    alan white Senior Member

    While a longer scarf is good practice, where epoxy's used there's a lot of latitude. Epoxy has amazing holding power on end grain, and as long as grain orientation (flat grain to flat grain, etc.) and species are similar, epoxy splice glue-ups need far less scarf length than other adhesives such as resorcinol or polyurethane. This should be considered if, for example, longer scarfs would interfere with hardware that would need to be removed. There would also be a savings on expensive sitka spruce, for example.
    PAR has more experience than me in such work, I'm sure, so I'd be interested in his opinion comparing scarf ratios with different adhesives.
     

  11. PAR
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    PAR Yacht Designer/Builder

    The scarf originally served a few functions, one was to provide more glue surface and another was to allow the hard point (glue line) to be spread over a longer distance, as to have less effect on the bending qualities of the lumber. Also the joint (the feather edge scarf) will permit moisture to drain out, rather then trap it like laps and other joints can. This is why scarfs are angled to slope away from the hull on rub rails or with the water flow on deadwood assemblies, so moisture can drain without harm. Generally, you want longer scarfs on pieces expected to receive fairly dramatic bends, Except some small boat masts, the majority of sticks don't need a 12:1 scarf in built up masts an 8:1 will do and you'll save some lumber in the process. You can't go wrong with an over length scarf, but you can if it's under length.

    I have a few different scarf jigs and there are dozens of variations of the same by others. For a few scarfs, I've found it's faster to cut them by hand then to set up a jig. A jig is nice if you have a bunch to do or your work will be finished bright.
     
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