Mast splicing?

Discussion in 'Multihulls' started by SpiritWolf15x, Mar 5, 2013.

  1. SpiritWolf15x
    Joined: Apr 2010
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    SpiritWolf15x Senior Member

    Hey everyone, I was wondering if anyone had any advice on what the "optimum" pop rivet pattern is when splicing a mast section back together where the sleeve is inside the mast. I was thinking a 5 point pattern with a square of four rivets with an extra in the middle on both sides of the mast with a line of rivets running down the front. Will this work? It's a tornado mast section so it'll have to be able to take those kinds of loads.

    Thanks,

    Wolf.
     
  2. Petros
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    Petros Senior Member

    Not sure I understand your pattern description. But lets see if we can work one out; the sleeve will take the bending and compression loads at the splice, it is the function of the rivets to transfer the loads from the mast to the sleeve and than back to the other part of mast. These kind of rivets slightly deform the metal outward around the hole that puts the surrounding metal in compression.

    Seems to me a kind of a diamond pattern would evenly stress the material. Straight lines of fasteners should be avoided.

    I would also add some sealant to the shank of each rivet before I installed it to seal out moisture.
     
  3. SpiritWolf15x
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    SpiritWolf15x Senior Member

    So make a diamond pattern on each side of the mast with rivets?
     
  4. Petros
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    Petros Senior Member

    yes, that is what I would do. Space them evenly.
     
  5. CutOnce

    CutOnce Previous Member

    SpiritWolf:

    Seeing as you are on the salty kind of water, I'd choose Monel rivets (stronger than aluminium) and use Duralac as a sealer/barrier between the mast & rivets. You need the sealer to mitigate the Galvanic corrosion of the dissimilar metals. Aluminium rivets just sheer off too easy.

    --
    CutOnce
     
  6. Petros
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    Petros Senior Member

    I would also put sealant between the sleeve and the mast to prevent trapped moisture at the the contact surfaces. It will be a messy installation, but worth the trouble I think. Adhesive sealant will also help distribute the loads from the mast to the sleeve. Smear it on the parts and slowly slide and twist them together, than wipe off the excess once it is assembled.
     
  7. Richard Woods
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    Richard Woods Woods Designs

    How long is your internal sleeve?

    Richard Woods
     
  8. oldsailor7
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    oldsailor7 Senior Member

    It is not sufficient to just coat the sleeve with epoxy before pushing it up and down into the mast sections.
    The inside of the mast has to be cleaned with cloth on a stick using acetone.
    Make sure the acetone has completely evaporated and then coat the inside of the sections with epoxy using a foam brush on a stick. Coat the sleeve with epoxy and then assemble the whole lot making sure the assembly is correctly aligned before leaving the epoxy to cure.
    Then, and only then, locate and drill holes for the rivets in a staggered pattern, as mentioned, and coat the rivet shanks with epoxy as you install them.
    I have successfully used this sequence so I know it works.
    The length of the sleeve has to be at least 5 X dia of the mast, with the two parts of the mast butting accurately together. This butting is most important as it prevents the rivets being loaded up in shear. The top and bottom edges of the insert should be filed off to a slight taper also before fitting so as not to provide a stress concentration point in the mast.
     
  9. Paul B

    Paul B Previous Member

    Professional sparbuilders would disagree with this.

    When the adhesive (epoxy is not the best) is applied and the sleeve is inserted into the spar, you want to use your fasteners to pull the sleeve up tight against the inner wall of the mast section.

    If you use the correct adhesive and technique the fasteners are really not doing any work after the cure. They could be removed, but are most often left in as it is less costly and acts as a redundent system.
     
  10. catsketcher
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    catsketcher Senior Member

    What's the best adhesive Paul? I have a mast to splice too

    cheers

    Phil
     
  11. Paul B

    Paul B Previous Member

    You should call your local 3M rep. Tell them your application and they will suggest the correct adhesive.

    Remember, if your spar bends the adhesive is not only in tension but also in shear. A rotating multi spar may not bend fore/aft like a mono rig, but it probably bends sideways a bit. So when discussing options with the guys at 3M you might want to mention this.
     
  12. oldsailor7
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    oldsailor7 Senior Member

    I don't agree at all.
    Unless the sleeve is a very tight fit in the mast sections, (and most won't be), there will be a gap,---however small.

    When riveting is initiated at one side, while the epoxy is still liquid, the gap will be closed---doubling the gap on the other side. This will affect the forming of the rivets on the other side, exposing them to malformation, which in turn makes them weaker in shear. Also drilling the holes for the rivets while the epoxy is still liquid exposes the area to metal swarf and fragments clogging the area. If the rivet holes are made once the epoxy is cured these possibilities don't exist, and the rivets can take up their design intention of helping the mast resist bending forces by acting in shear. Epoxy, although it is strong in compression, does not have sufficient adhesive properties to handle the shear forces produced by the mast bending. This is why the rivets are needed.
    Other adhesives are even worse.

    I would like to hear from a professional spar builder on this subject.
     
  13. Paul B

    Paul B Previous Member

    Nice to hear you know better than the people who do it for a living.

    I am amused by some of your assumptions about the methodology.
     
  14. SpiritWolf15x
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    SpiritWolf15x Senior Member

    About 3feet, I took the pieces to ProTech in North Van and they did some measures and said about 1.5feet in each end should be plenty.

    The guys at ProTech said on assembly to use some 5200 silicone, coat the inside where the insert is and to use SS rivets. I've epoxy out the wazoo so i could easily switch from Silicone to that if it'd work better.

    I bought 20 3/16 x 3/8 long SS rivets, will these work?
     

  15. oldsailor7
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    oldsailor7 Senior Member

    Lol Paul. I am happy I could amuse you. :rolleyes:
     
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