Aluminum mast

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  • 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


    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 | Anonymous member
  • 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

    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?

  • 30 Apr 2019 05:07
    Reply # 7310853 on 7309942

    Hi John,

    if you Google flag pole manufacturers and look at their hurricane rated poles these will serve well as a mast. Most of the manufacturers are in the east  and south of the USA so transport is the big cost. There are also manufacturers in China that can be accessed through Alibaba, they will build a custom section to your specs and their prices are very competitive, however transport effectively doubles the cost here in New Zealand, it may be less in Canada, possibly worth a bit of investigation. 

    My previous boat, Arcadian, had fiberglass masts that were not tapered and these performed well although they did not look as elegant as tapered masts. The layup thickness reduced from about an inch at the partners to about a quarter of an inch at the top, so there was a slight amount of taper on a ten inch internal diameter mast. The mast I have built for my present boat, Gypsy Rose, is a six inch diameter aluminium section with a tapered solid wood topmast. This was relatively easy to make and looks reasonably elegant, so is, I think, a good compromise.

    All the best, David.

  • 30 Apr 2019 03:55
    Reply # 7310649 on 7309942

    The top part doesn't need to be wood either, smaller diameter alloy tube gives a kind of taper. Here is a "tapered" mast made in three over-lapping parts, from scraps: part of a 5" flagpole, a 4" diameter yard off another rig, and ending with part of a dinghy mast about 2.5" - and a lump of pine with a turned (round) stub which fits up inside the base to make a heel - and a drain hole.


    The short transition taper between sections (the white bits) was just done with epoxy and glass fibre bandage. It was very quick and easy to do, and seems OK. 

    Last modified: 30 Apr 2019 04:09 | Anonymous member
  • 30 Apr 2019 01:59
    Reply # 7310486 on 7309942
    Anonymous wrote:

    what does everyone think of a mast without taper? I can get aluminium in the 7” x 3/8 6061 t-6 but I can’t get it in tapered (flagpole)


    I have a friend with a 25ft Top Hat (2.5 tons) that has an untapered mast.  He has no shrouds but has a forestay on which he sets a small jib.  The boat has sailed a lot of coastal miles.  Taper is obviously better if you can get it.  3/8th inch wall thickness is very heavy.  5-6mm is more than enough.  With an untapered mast I think you will put more load on the step and partners but it can be engineered strong enough.  Also looks less elegant, but I cannot see that it would be unacceptable.  You could consider a 6m lower alloy section and add an epoxy-sheathed, tapered, timber top section, and epoxy sheath it up to and over the joint.
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