Aluminum mast

  • 06 Sep 2019 09:41
    Reply # 7866623 on 7309942

    John,

    Hollow vs solid mast: that's a question of stiffness to weight ratio, mainly. As with an aluminium mast being stiffer for the same weight if you go for a larger diameter and thinner wall, so a hollow wooden mast will be larger in diameter than a solid mast, but stiffer, weight for weight. But, pragmatism should rule. Many people find that the hybrid is easiest to achieve, but if you have access to good grown poles, then go for it.

    You're right, the "boom" is really just another batten. The only reason to make it a bit heavier is that the sheet doesn't hold it down as well as it does the higher battens. That's more about a tidy look than about efficiency, and luff tension is the same, if the sail is flat. With a cambered sail, though, a scalloped luff tends to detract from our efforts to achieve a good shape, so some downwards pull is good - either heavy-ish battens, or downhauls or a lower LHP will help. It won't move the CE forward, though. The whole sail can be moved forward to do that.

  • 06 Sep 2019 00:51
    Reply # 7866246 on 7309942
    Deleted user

    Thanks all of you who responded. Please take no offence to my preference for one mast material. It really is just a ocd thing.

  • 06 Sep 2019 00:49
    Reply # 7866242 on 7309942
    Deleted user

    After much searching I can’t seem to find a aluminum flagpole to match the spec that I was given by the naval architect.  I have read a reread the various ways all of you have made masts and although the hybrid mast works just fine I can’t swallow it. It simply rubs me wrong in the way certain noises bother some people (irrational) lol.

       I’m a accomplished carpenter and I would have no problem making a hollow mast and dry Douglas fir is plentiful here. But I’m leaning towards a solid timber as I can get a hydro pole pre wood preservative. I would build my partners to a large enough size to accommodate a hollow mast just in case. Can anyone explain just how different my boat will sail with a hollow verses solid mast?

      On another note, I’m having a hard time wrapping my head around the idea of such a heavy boom when all the battens are small. I understand the yard being big but when the wind is up now I’m reefed and relying solely on the battens. And also what about luff tension? Is it needed?  When beating will I want to move my ce forward like I do with my Cunningham on my Marconi rig?

  • 01 May 2019 22:01
    Reply # 7315124 on 7314997
    Anonymous member (Administrator)
    Anonymous wrote:

    Whether welding will reduce the strength of the mast, or not, depends of what temper you start with. With a 6063-T6 tube, the strongest alloy, you will probably lose a lot strengt when welding, just where strength is needed.


    Arne


    Guessing that you meant 6061 T6.

    Phil


    You are right, Phil.

    6063-alloy is also strong, and many have used it, but 6061-t6 is even stronger.

    I don't have access to 6061-t6 here, but use 6082-t6 for masts, which is supposed to have a yield strength of 250MPa.

    Arne

    Last modified: 01 May 2019 22:03 | Anonymous member (Administrator)
  • 01 May 2019 21:11
    Reply # 7314997 on 7313596

    Whether welding will reduce the strength of the mast, or not, depends of what temper you start with. With a 6063-T6 tube, the strongest alloy, you will probably lose a lot strengt when welding, just where strength is needed.


    Arne


    Guessing that you meant 6061 T6.

    Phil

    Last modified: 01 May 2019 21:13 | Anonymous member
  • 01 May 2019 08:19
    Reply # 7313596 on 7309942
    Anonymous member (Administrator)

    John,

    this subject has been discussed several times, for instance here:

    https://junkrigassociation.org/technical_forum/5070195?mlpg=10,6

    (copy - paste link...)

    Jami Jokinen in Finland ended up making and sailing away with a 2-section aluminium mast.
    Graeme did a gluing test on aluminium, and the conclusion of that was that the aluminium surface should be sanded and then coated with epoxy resin right afterwards. This gave very strong bonding.

    Whether welding will reduce the strength of the mast, or not, depends of what temper you start with. With a 6063-T6 tube, the strongest alloy, you will probably lose a lot strengt when welding, just where strength is needed.


    Arne


    Last modified: 01 May 2019 08:21 | Anonymous member (Administrator)
  • 30 Apr 2019 22:55
    Reply # 7312851 on 7309942
    Deleted user


    I wonder how much effect the welding has? Any engineering anyone knows of? The flagpole The sleeve inside with proper bury would take the load in theory. 

      My worry about the flagpole is strength of course. I talked with a couple who converted their boat (same boat I have. Same designer) and they said there’s works great with the flagpole but I want take my boat offshore. They sail out of San Francisco Bay.

      Oh I should say my boat is a rawson 30. Also I should mention I’m a carpenter and I can make anything out of wood. I simply don’t want the maintenance of wood and aluminum potentially is lighter. 

    Last modified: 30 Apr 2019 23:09 | Deleted user
  • 30 Apr 2019 21:36
    Reply # 7312722 on 7309942

    John, there is a fairly lengthy thread called "Mast materials and specifications" with some discussions you might look at, some of it speculative. No-one recommends welding. 

    To bridge the gap between diameters inside the joint, if the difference is small, two epoxy and glass bandages will do. For a larger gap, thin strips of wood can be epoxy glued to the inner tube, faired and fitted so as to maintain alignment. 

    The overlapping sections need sufficient "bury".

    The choice of glue for joining the sections has been a subject for discussion. I have found that epoxy glue sticks well to aluminium if you prepare it properly. There is another school of thought which suggests a more flexible glue is preferable (polyurethane rubber type) as a rigid glue, in theory, creates a hard spot.

    My own speculation is that the outer bandage and fairing cone is probably sufficient to hold two well-fitted sections, with just a minimum of glue inside the joint, and I am putting this to the test on the small mast shown in the last post. One way or another, the joint together with the lip created by the fairing cone must withstand downward pressure (from halyards etc) - and twisting.

    I don't think there has been any report of a mast failure at the join of a composite mast, so far. If there has been, I hope someone will chime in and provide a reference.

    Last modified: 30 Apr 2019 22:28 | Anonymous member
  • 30 Apr 2019 07:34
    Reply # 7311019 on 7309942

    hi john

    John Evans wrote:

    …I like the idea of sleeping smaller sections into each other enough for alignment and welding them…

    i would rather glue than weld the sections. the thermal stress while welding modifies the internal structure of the alloy and weakens the mast.

    ueli

  • 30 Apr 2019 05:41
    Reply # 7310928 on 7309942
    Deleted user

    The designer doesn’t like what I can get for flagpoles which is unfortunate. I like the idea of sleeping smaller sections into each other enough for alignment and welding them and fiberglassing the taper is a great idea.

      I need 38’ above deck if memory serves me correct. So 7” then 6 1/4 (if I can get that size) then 5.5 and etc perhaps the thickness should change near the top.  

      Any ideas how this would work?

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