Best Place To Cut/Splice Mast

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

  1. PAR
    Joined: Nov 2003
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    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Don't cut the mast at an angle, make the cut as square as practical, preferably with a metal cutting band saw, that can insure a perfectly true cut. Sleeves can be relatively inexpensive or very costly, depending on the extrusion section used. Sometimes (again, depending on section) you can cut out the car or internal track bosses, just above and below where the sleeve will live. Cut the mast above the lower spreader, where the bending loads will be modest. The sleeve should be a minimum of 4 times the widest dimension of the mast and fishmouth or elliptical cut on the ends of the sleeve wouldn't hurt, though most often it's simply a straight cut. Lightly ease all cuts, especially at the track joint and assemble, typically with sheet metal screws initially, which sucks it together. After you're satisfied with the fit, replace the screws with countersunk rivets. This type of repair is pretty common, though now, many are also using epoxy, to insure things stay put, which is a good idea. With any luck it's the DM-800 extrusion, which is pretty easy to work on.
     
  2. tom28571
    Joined: Dec 2001
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    Location: Oriental, NC

    tom28571 Senior Member

    Many, maybe most typical masts are supported by a common stay system consisting of upper side stays and lowers rigged both fore and aft of the mast location. Failure of one upper side stay is a common cause of mast failure. This means that the lowers still support the bottom section of the mast and THIS is the most likely reason most tend to break near or just above the middle height location.

    Splices are common in masts, even new ones and are no cause for concern if done right.

    This mast is much more complicated than that and, while a properly executed the cut can be made almost anywhere, the services of a NA or competent rigger is good practice.
     
  3. BertKu
    Joined: May 2009
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    Location: South Africa Little Brak River

    BertKu Senior Member

    I am delighted that the experts have spoken. Not at an angle but 90 degrees. I was under the impression that it would be the same as gluing a drive belt as a temporary measure until the new belt has arrived. One is never too old to learn. Boatcat65, you can't go wrong anymore, you should now have all the answers for yourself from PAR, TOM and Gonzo. Bert
     

  4. Boatcat65
    Joined: Jul 2016
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    Location: Seattle

    Boatcat65 New Member

    Thanks all. Seems 25-30% of the distance from the bottom spreader to the middle spreader is the sweet spot. I was leaning towards cutting at the bottom spreader... keep the weight of the splice as low as possible while beefing up a critical load area but can see how it might be best to spread out the stressed areas.

    Shipping as a single piece is certainly possible but involves not just the main trip but also taking it to and picking up from the depots. For the record 75' is the practical upper limit for over the road permits etc.
     
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