Mast splicing?

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

  1. Samnz
    Joined: Nov 2008
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    Samnz Senior Member

    Yep that will be fine, the rivets arent doing much, most of the load is compression and taking up by the perfect? butt join. (depending on where the break is?) I have done a successful join with a way smaller sleeve. I would use Sikaflex as the joining compound and predrill and dryfit the whole shitfight if possible. Monel coated stainless is preferable but if you already have stainless rivets you can use durelac or jut plenty of sika to keep the moisture out/off them
  2. Paul B

    Paul B Previous Member

    This is very good advice.

    Just be prepared with the tools required to pull the thing apart.
  3. gonzo
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    gonzo Senior Member

  4. Ilan Voyager
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    Ilan Voyager Senior Member

    You're almost right but unhappily the joint is on the upper part of a 3/4 multihull rotating mast where flex is maximal (this flex controls the leech and the power of the sail) so the rivets will have a great deal of work and must fit very tightly.
    The problem is not to introduce a hard point (where the metal has twice the thickness) with an abrupt change of stiffness (where there is only one thickness, the mast itself), specially in the lower part where a hole for halyard is made.
    The concentration of the stresses is this part may break the mast. And surely the bend won't be even.
    In reality is not a very difficult work but surely it must be done with the greatest care after being well designed.

    There are 2 techniques applicable in this case:
    1- create a transition of inertia, and thus minimize the hard point. In clear words to have less metal at the beginning and end, and the max of metal at the butt joint. This can be very simply done by cutting "vees" on the inside tube.
    2- get the best fit possible, at least where are the rivets. In clear the inner tube must be soft enough to be applied on the mast when riveting.
    The trick is to use a heat treatable alu, happily it's the most common alu you can find, the 6xxx series. At 98% probabilities the inner tube is made with a 6061 state 5 or 6.
    You must simply soften it temporally. It's very simple: you need a propane plumbing torch and some white soap for hand washing, the old one in small bars, found everywhere for a few pennies.
    The white soap is applied in the inner side with no contact with the flame of the torch. You heat evenly the piece of alu with the torch. When the soap blackens, you have got the right temperature 180 degrees Celsius, do not heat more and the aluminum is now at state 0, very ductile. Let it cool, it's ready.
    While riveting the aluminum will be easily deformed by the rivets and will be put in contact with the mast with a tight fit. The other advantage of importance it's you cannot deform the mast, as the inner tube is softer than the mast. SS rivets are very hard pullers and can dent the mast if the inner tube does not fit and is too hard...
    The aluminum will began to harden naturally in a few days and be be at state 3 to 4 in 10 to 15 days. It's enough to get a good strength. After aging a few months the alu will be almost as strong as before.
    Those who work aluminums 6063 and 6061 know very well these facts about heat treatable alus.
  5. oldsailor7
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    oldsailor7 Senior Member

    We used to heat treat alloy tubes by dipping in a salt bath heated to the right temp, but that is not a procedure an individual can handle.
    Using a blow torch will work, but you have to be very careful to get the heat evenly distributed over the whole area or you will end up with hard spots, or worse still, overheated areas.
  6. Ilan Voyager
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    Ilan Voyager Senior Member

    You're right, but in reality the risk is small with the spots of soap that are an excellent indicator... Light brown 120°C, brown 150°C, dark brown 180°C, black too's not for jets but just a small boat.
    It's easy to heat evenly a simple small piece of tube with the same thickness every where. (not the same in longer or complex pieces...)
  7. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    Interesting thread, seems like with a small sleeve such as this it may fit in your oven in the kitchen if momma will let you.

  8. SpiritWolf15x
    Joined: Apr 2010
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    SpiritWolf15x Senior Member

    This is all sounding too complicated and is giving me a headache... I'm going to say "screw it" and have them build me a new spar... Ultimately it'll work better than a patched together Tornado rig would anyways.
  9. killyian
    Joined: Mar 2018
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    Location: Carriacou Grenada

    killyian New Member

    Just in case like me you are interested in two pieces of mast
    This is 1980 boat with 47 ft mast joined at 40 ft

    Attached Files:

  10. bruceb
    Joined: Nov 2008
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    bruceb Senior Member

    Back in the early 80's, Hobie dealers were required to cut the last 7' or so off of every Hobie cat mast and replace it with a fiberglass non conducting replacement top section. The replacement job was usually done in the dealer's driveway, climate control was very limited :), and there was very little training.
    Slop on some resin, pop in a few rivets, wait 24 hours and give it back to the customer. Done! Most of those masts are still as tight as the ever were. Maybe not the best way, but don't overthink this either.
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