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Re: mast welding

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  • pp01138
    Are you sure the pipe you have is even the proper alloy for mast use? Aluminum is available in a bunch of alloys, all with very specific uses. A lot of pipe
    Message 1 of 19 , Apr 5, 2005
      Are you sure the pipe you have is even the proper alloy for mast use?
      Aluminum is available in a bunch of alloys, all with very specific
      uses. A lot of pipe alloys are very soft and bend easily. I am involved
      in ham radio, and you wouldn't believe how many antennas you see
      mounted at a 30 deg angle because someone found a neat section of
      aluminum pipe to use as a mast.

      I have had quite a bit of experience fabricating different things from
      aluminum, including tubing, and can say without hesitation that you
      should absolutely not weld the joint. It will be either brittle and
      break or too soft and bend. This will be true even if you weld with a
      plug inside. Aluminum has such a low melt point that annealing and
      tempering occur at surprisingly low temperatures. Drastic changes can
      occur at only a few hundred degrees. Unfortunately, to get a good weld
      penetration adn avoid a brittle joint, a pipe as large as this would
      need to be preheated into this range to weld. The only answer for
      welding is to weld (probably with a sleeve inside unless the pipe is
      very thick, and then heat treat. If you can find a flag pole or light
      pole manufacturer who can do this cheap, fine. However, sometimes the
      best thing is to just buy what you need.

      As to the sleeve method, I suspect it will work, but this is an awfully
      big pipe to join that way. If you do it, I really think fit is
      critical. If the fit is loose at all, the joint will quickly flex/wear
      itself away. Using epoxy may work, but you should be sure you
      understand the compressive loads on the ends of the plug when the mast
      is loaded. They are likely enormous. Think of a 20 foot lever working
      with a 6 inch fulcrum apacing. That's why the plug needs to be long.

      Also, not flaming, but the idea of splitting the inner tube is bad. It
      would rob the plug of a lot of its strength.

      I am and engineer by trade and have done a lot of machining in my home
      shop, so this is not totally opinion. While a lot of these types of
      ideas work on small boats and masts, when your start talking about a 40
      footer 8 inches ID, I would get a little nervous trusting my life to
      them.
      --- In bolger@yahoogroups.com, "fritzdfk" <gaffcat@h...> wrote:
      >
      > I need to join two 20' lengths of 8" schedule 40 aluminum pipe to
      make
      > a 40' mast for Double Eagle. Various people have given me suggestions
      > as to how to do this, but I don't think I have gotten the definitive
      > answer. With the chinese gaffer rig I need a smooth exterior. Most
      > agree that I need an inner sleeve and one engineer type said that an
      > inner sleeve 4' long with twice the wall thickness of the outside
      pipe
      > was needed. As any given pipe may not be perfectly round the sleeve
      and
      > the interior of the pipe would need to be machined. Does the sleeve
      > need to be 4' long? A machine shop has given me a quote for a 2'
      sleeve
      > at a cost of around $1000 just for machining. Is there another way?
      Any
      > structural engineers out there?
      >
      > fritz koschmann
    • Paul W. Esterle
      Fritz, Since none of the replies so far seem to have been based on actual, successful, repairs, please look at the following link:
      Message 2 of 19 , Apr 5, 2005
        Fritz,

        Since none of the replies so far seem to have been based on actual,
        successful, repairs, please look at the following link:

        http://www.caphorn.com/sections/dematage/capsized.htm

        It recounts the successful repair of an Alberg 30 mast with a sleeve in the
        Chatham Islands. The Alberg 30 went on to complete a successful
        circumnavigation.

        Paul Esterle
        Freelance Boating Writer
        Member, Boating Writers International
        pages.preferred.com/~pesterle/
        www.smallcraftadvisor.com
        www.captnpauley.com
      • Wayne
        ... Yes, freezing with dry ice works. Or at least it works for bronze bushings in steel plates where I am employed. The machinist turns the bushings 10 or 20
        Message 3 of 19 , Apr 5, 2005
          --- In bolger@yahoogroups.com, "Don Taylor" <nospamforme@c...> wrote:
          ...(I read somewhere that
          > one technique is to use dry ice to chill the sleeve which will reduce
          > its diameter, slide it into the mast sections and let it warm up and
          > expand. I don't know if this is a for real suggestion.)

          > Don.

          Yes, freezing with dry ice works. Or at least it works for bronze
          bushings in steel plates where I am employed.

          The machinist turns the bushings 10 or 20 thousandths over size and
          freezes them overnight in dry ice. Next morning he drops the bushings
          in their holes in ROOM TEMPERATURE steel. By lunchtime they are quite
          snug. Do not heat the larger piece! The hole will expand and the forzen
          piece won't fit OR when the heated piece cools the hole will be too big.

          If you really want to weld something, weld up a tabernacle for your
          doug-fir spar. Put a doubler plate under the deck and a compression
          post (same doug-fir, we got to get some wood in this boat, eh?) to the
          keel and Bob's your uncle! No hole in your watertight deck!

          Wayne
          In the Swamp.
        • Wayne
          ... the ... Disregard, wrong boat. Wayne In the Swamp.
          Message 4 of 19 , Apr 5, 2005
            --- In bolger@yahoogroups.com, "Wayne" <wtorry@v...> wrote:


            > If you really want to weld something, weld up a tabernacle for your
            > doug-fir spar. Put a doubler plate under the deck and a compression
            > post (same doug-fir, we got to get some wood in this boat, eh?) to
            the
            > keel and Bob's your uncle! No hole in your watertight deck!

            Disregard, wrong boat.

            Wayne
            In the Swamp.
          • Bruce Hallman
            Can anybody identify the Bolger Leeboard Sharpie about 2/3rds the way down the NEW page presently on Duckworks? My guess is a Cynthia J, modified to have a
            Message 5 of 19 , Apr 5, 2005
              Can anybody identify the 'Bolger Leeboard Sharpie'
              about 2/3rds the way down the "NEW" page presently
              on Duckworks?

              My guess is a Cynthia J, modified to have a Cat Yawl rig.
            • Jamie Orr
              You might try Brion Toss website for advice on this, he has a forum called Spartalk. Brion answers many of the posts himself, and is about as knowledgeable
              Message 6 of 19 , Apr 5, 2005
                You might try Brion Toss' website for advice on this, he has a forum
                called Spartalk. Brion answers many of the posts himself, and is
                about as knowledgeable as you'll find on the web. The website is at
                http://www.briontoss.com/

                Jamie Orr

                --- In bolger@yahoogroups.com, "fritzdfk" <gaffcat@h...> wrote:
                >
                > I investigated riveting or using machine screws rather than welding
                > and was told it wasn't practicle for that size pipe. There would
                > still be an inner sleeve and the fasteners required would weaken
                the
                > structure too. You would end up chasing your tail, more fasteners
                for
                > strength but each one you add weakens the joint.
                >
                > Welding weakens the aluminum by about 50% but that is where the
                inner
                > sleeve comes in. The weld has full penetration in the outer pipe
                and
                > penetrates the inner sleeve slightly. You should end up with
                > structural integrity roughly equal to a solid piece of pipe.
                >
                > I think the fit between the outer pipe and the sleeve would have to
                > be a very close fit to work. Assembly would involve freezing the
                > sleeve and heating the pipe. There is no smaller stock size of pipe
                > that is close to fitting inside the outer pipe.
                >
                > I did fax Bolger a week ago about this and got a hurried reply
                saying
                > they would get back to me in ten day or so, they are very busy.
                There
                > were no details for this in the original plan.
                >
                > I had thought of the light poles before, I'll have to look into
                that.
                >
                > fritz koschmann
              • jhkohnen@boat-links.com
                At your work the temperature differential between the cold bushings and the room-temperature steel is sufficient for the purpose, but if it isn t, heating the
                Message 7 of 19 , Apr 6, 2005
                  At your work the temperature differential between the cold bushings and the
                  room-temperature steel is sufficient for the purpose, but if it isn't,
                  heating the steel will make the holes _larger_ as the steel expands. I know
                  this from experience, not just from common sense, from removing and
                  installing bearing races, rocker spindles, gudgeon pins and other
                  paraphernalia in car and motorcycle engines.

                  On Tue, 05 Apr 2005 20:47:22 -0000, Wayne wrote:
                  > Yes, freezing with dry ice works. Or at least it works for bronze
                  > bushings in steel plates where I am employed.
                  >
                  > The machinist turns the bushings 10 or 20 thousandths over size and
                  > freezes them overnight in dry ice. Next morning he drops the bushings
                  > in their holes in ROOM TEMPERATURE steel. By lunchtime they are quite
                  > snug. Do not heat the larger piece! The hole will expand and the forzen
                  > piece won't fit OR when the heated piece cools the hole will be too big.
                  > ...

                  --
                  John <jkohnen@...>
                  http://www.boat-links.com/
                  I Can't take a well-tanned person seriously. <Cleveland Amory>
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