Splicing two mast halves together?

Discussion in 'Multihulls' started by SpiritWolf15x, Jun 1, 2010.

  1. SpiritWolf15x
    Joined: Apr 2010
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    SpiritWolf15x Senior Member

    I've been given two halves (approx') of a 48' rotating aluminum mast section, the boat they came off was a 35' racing cat.

    I'm wondering if it would be possible to shorten the two pieces and pop-rivet them back together to make a 46' spar for my Buccaneer 33 Trimaran.

    Any and all input welcome.

    -Wolf
     
  2. Petros
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    Petros Senior Member

    It can be done if designed properly, it would add weight as well as extra thickness where the splice occurs. It might be possible to put the splice on the inside but that would require a custom extrusion I suspect. It is an engineering design issue, and I suspect not to be done without proper guidance. You have large compression loads, as well as severe bending forces, on a typical mast installation. This creates a buckling failure mode, which is not easy to reliably predict, so most buckling design methods have large safety factors.

    When you say "two halves" does that mean it was broken off there? Or is this an assembly joint?
     
  3. SpiritWolf15x
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    SpiritWolf15x Senior Member


    it snapped between the upper and lower spreaders.
     
  4. Paul B

    Paul B Previous Member

    You may not be aware, but most masts are built from aluminum extrusions of 40 feet. That is due to transportation costs from the mill to the sparbuilder. In some cases special runs can be made at up to 45 feet or so, with a higher shipping cost.

    So if you walk along a marina and have a look, practically every mast you see longer than 40 feet has a splice in it.

    Generally the sparbuilder will take a section of the same extrusion, cut out the back, and squeeze it inside the two halves that need to be joined. The splice is held together with plug wleds, screws, or rivets.

    If you use rivets be sure to use structural rivets. Monel is the preferred rivet material. Use an isolating material between any fasteners and the aluminum to ensure there is no corrosion.
     
  5. Richard Woods
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    Richard Woods Woods Designs

    You're always rather coy with your posts!!

    Was this a recent breakage, like on Saturday??

    No problem rejoining a mast, as Paul B says most are sleeved anyway. Its just a bit of a fiddle cutting a sleeve and making it fit. Usually you cut off the sail track and that reduces the size enough to push it inside. You'd need say a 1.5m min sleeve though.

    You could even use my pop rivetter to join it all together again. (I think Bob still has it)

    So you'll either have a short mast or you'll need to get a similar section to make a sleeve (maybe the Dragonfly guys can help??) You cannot get a flat piece of aluminium sheet and bend it accurately enough, unless you have access to a good workshop (Bob again?)

    Hope to see you sailing soon

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  6. SpiritWolf15x
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    SpiritWolf15x Senior Member

    Ha, hey Richard, so you've found me out eh? :D

    Yeah I figured since they are just going to throw it away anyways, I'd make myself a nice 46' mast for my tri.
     
  7. Richard Woods
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    Richard Woods Woods Designs

    Years ago I did make an external glass/epoxy sleeve to join a mast. From a distance you couldn't see the bulging join.

    So it is a possible option. You'd probably need 10mm of glass on the outside and of course ensuring the mast is straight and true is always tricky

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  8. SpiritWolf15x
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    SpiritWolf15x Senior Member

    I have some bi-axle and 18 oz. cloth I might be able to use. Could a glas sleeve be internal or would it have to be external?
     
  9. cavalier mk2
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    cavalier mk2 Senior Member

    I have heard of people using internal wood plugs. It is something of a boondocks solution compared to a aluminum plug and has to be well preserved in epoxy. The advantage is it is easy to shape, if you make it smaller in diameter you could cover it in cloth or use the same principle for a mold for a fiber internal splice section. In the tradition of auto panel beating a wood plug can also be used to form sheet aluminum. The 2 opposite edges of the sheet should be held with sheet metal screws in a slot cut in a dowel or timber so even bending/wrapping can be applied. If the dowels are made long you have handles to use while bending. Make the sheet large enough to wrap with lots of overlap for easy shaping then trim to size . You could use a circular saw with the correct blade set so it won't quite cut through then bend break and file/sand. Not being afraid to use body hammers when needed and good rivets are a must. Using a good adhesive sealant on final assembly can fill any small imperfections but be sure it can handle the heat of a metal mast in the tropics etc....You should also paint or anodize the plug when completed before final assembly.
     
  10. Richard Woods
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    Richard Woods Woods Designs

    Anything is feasible at the design stage. Making it is a different matter. Clearly it is much much easier to make an external sleeve. I don't know how you'd even begin to make one on the inside, given that it has to be a good, touching fit all round.

    And don't forget the halyards

    Richard Woods of Woods Designs

    www.sailingcatamarans.com
     
  11. SpiritWolf15x
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    SpiritWolf15x Senior Member

    I think I'm going to be going with an external sleeve, finding a donor section to cut up is proving difficult.
     
  12. Stumble
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    Stumble Senior Member

    If you get in touch with the original manufacturer of the mast with the profile number of it, they should be able to knock out a sleeve pretty easily. Likely they have some scrap laying arounf that will do the trick (though they will charge you like it is new).

    Either way I doubt it will be that expensive.
     
  13. aussiebushman
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    aussiebushman Innovator

    Yes and a sleeve works well. My 11 meter mast was constructed from two identical sections and fitted with an external alloy sleeve about 3 metres long made from a broken mast section. You would have to look carefully to even see the sleeve. Twin diamond spreaders were added and the whole rig was "bullet proof."

    I'm interested in Richard's comment about a fibreglass sleeve. Did it completely enclose the mast?

    Alan
     
  14. SpiritWolf15x
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    SpiritWolf15x Senior Member

    Anyone in the Greater Vancouver area know of a mast section supplier?
     

  15. cavalier mk2
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    cavalier mk2 Senior Member

    They charge too much for the crane down here. Since you've got to splice the mast you might want to rework the step and heel.
     

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