Best Place To Cut/Splice Mast

Discussion in 'Boat Design' started by Boatcat65, Jul 17, 2016.

  1. Boatcat65
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    Boatcat65 New Member

    Hi! Need to transport an 80' mast and it looks like the only economical way to do it is to cut and splice with an insert/sleeve. The question is where? It's an aluminum triple spreader rig, keel stepped, masthead rig. A hydraulic backstay is used from time to time to tighten/bend the rig. We spend some time offshore but not racing or driving the boat that hard. So given the forces involved where would be the best place to make the cut? Longest piece can be 60'. TIA
     
  2. BertKu
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    BertKu Senior Member

    My gut feeling tells me to split it 58 by 22 feet. My logic, whether wrong or right, tells me that the greatest force is at the middle of the mast. That is thus the wrong place to split it. From middle to upper point the forces are also high. Thus my logic tells me to do it at 22' and their it will be thicker and stronger to make an insert/sleeve.
    I am building now a simple mast for my little converted sailing boat. And came to the conclusion that it depends whether you have a number of metal wires running from the mast to the wires from hull to top of the mast or only 2. But don't come in a year's time and tell me that I was wrong. It is just my gut feeling. Bert
    Bert
     
  3. Tiny Turnip
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    Tiny Turnip Senior Member

    Just a thought - any mileage in selling the mast where it is, buying a replacement at the destination, and saving the transport costs and the cost of the work, which might cover any price difference. No idea on whether your locations would work for this, or if the sums add up, but might be worth half an hour investigation.
     
  4. TANSL
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    TANSL Senior Member

    I do not know where the greatest force on the mast. I think that with the data we have, nobody can know. However, I doubt that the greatest load (not only force) on the mast occurs at its midpoint. Would have to know how rigging.
    We should not be guided by the "intuitions" that everyone has.
    Regardless of all this, in my opinion, you can cut where you want if then the connection is done correctly.
     
  5. gonzo
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    gonzo Senior Member

    Have you considered a train auto boxcar? They are 86 feet long.
     
  6. fcfc
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    fcfc Senior Member

    Have you looked at Gutelle Book ?

    He speaks (briefly) of mast sleeving in volume 3. According to him sleeve should be placed 25% of spreader spacing, above or under any spreader. He also give rough sizing for sleeve.
     
  7. BertKu
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    BertKu Senior Member

    Maybe Tansl is right, that I am not an expert, but all the masts I have seen broken on a boat were basically in the middle. Like I also said, it depends on the number of spreaders (sorry I forgot the name and called it wires etc.) I would not just cut it somewhere but more towards the bottom. Boatcat65, Google for all broken masts and then make your mind up. Bert
     
  8. TANSL
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    TANSL Senior Member

    BertKu, you are quite right, it depends on so many things we do not know that we can not venture anything. How are the masts, and rigging, you've seen broken ?. Are they equal the OP's mast and rigging?
     
  9. BertKu
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    BertKu Senior Member

    Tansl, I am not going to argue about it. Mainly from films, photo's and you are right, there are so many variables, I am very surprised that the real experts haven't responded. Look at the paintings of old sailing ships and also modern sailing disasters yachts. I don't think they sucked the scene out of their thumb. Bert
     
  10. BertKu
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    BertKu Senior Member

    Tansl, A bow and arrow has the same problem. Have you ever seen an bow broken at 1/3 or 1/4? Mostly in the middle where the greatest forces are. That is in my view with a mast also and the spreaders helps transfer some of the tension to the outside wires from top of the mast to the hull. Also off course where the weakest point of the mast is, lots of pop rivets holes etc, Bert
     
  11. BertKu
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    BertKu Senior Member

    Gonzo, in your lifetime, you must have inspected lots of broken masts? Your idea is a good one, provided the American railways are more careful than in the rest of the world, except if Boatcat65 travels with the mast. Bert
     
    Last edited: Jul 18, 2016
  12. TANSL
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    TANSL Senior Member

    BertKu, I am delighted to exchange views with you and, if our conversation does something to OP, then we all have won something.
    I have not seen broken masts. That is, yes I have seen but I could not analyze why are broken and why are broken by a particular site.
    Among the many variables there, as you say, they are objects riveted to the mast, for example.
    You may be totally right, all I wanted to make clear is that without analyzing the mast and its circumstances, no one should give advice. Moreover, ask for advice without explaining all the variables that can intervene in the problem, it does not seem very logical.
     
  13. gonzo
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    gonzo Senior Member

    I find that one of the places masts break is at the gooseneck. This is usually by a uncontrolled jibe. Otherwise, it is often caused by a failure of the rigging, and they break right above the highest place they are supported.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I've inspected a lot of broken masts and I've broken quite few too. They don't seem to break in the middle, but usually at a load point. Typically, spreader base locations, goosenecks, partners, stay and shroud tang locations, etc. I've seen a few that went so out of column, that they buckled in areas well away from any hard point. It also depends on how it gets broken. Running into a bridge will break a mast differently, than a huge gust with too much area on.
     

  15. BertKu
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    BertKu Senior Member

    Boatcat65, the experts have spoken and you can now make your conclusion from it. a) check possible weak points where they are located, spreaders, etc. b) After you have cut and place a sleeve, one can read between the lines of your thread, that you will travel to re-assemble the mast again. In that case take Gonzo's advice, don't cut and travel with the mast in a boxcar of 86 feet. If not possible, take the French member's advice and cut 25% away from the spreader mountings towards the bottom of the mast. c) If you don't take Gonzo's advice and have to cut, do it at 45 degrees. i.e. not 90 degrees. so that the expected forces are spread over a larger cut. and the sleeve will hold better. Here daiquiri could maybe give you good advice. d) At the end, you probable will cut it roughly where I proposed the cut i.e. between 22 and 30 feet from the bottom. But you have to check all your weak spots first. Because nobody is able without photo's and knowing the weak spot's be able to advise you. Bert
     
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