Mast materials and Specifications

  • 26 Apr 2017 14:22
    Reply # 4780332 on 4777534
    Graeme Kenyon wrote:

    (Sorry Scott, and David Webb, for crossing over your interesting discussion on conduits. Perhaps I should have tried to start a new thread. Haven't been on forum before.)

    No worries - I think I'm the interloper, given the time frame.

    David Webb:  Thank you - that's exactly what I'm going to do, I think.

    Last modified: 26 Apr 2017 14:22 | Anonymous member
  • 25 Apr 2017 11:06
    Reply # 4777822 on 1306051

    Thanks David I did realise that and it was going to be my next question - could a cone be built up with fibreglass tape bandaging and some fairing? I have had no experience with aluminium and don't know how well it goes with fibreglass.  Just trying at the moment to think of ways of using what I've got - not always a good way to proceed, I know.

  • 25 Apr 2017 10:53
    Reply # 4777804 on 1306051

    Graeme, remember that if there's a join anywhere above the foot of the sail, the transition has to be very smooth to permit the sail to drop readily. This means that a way of making a long conical fairing of some kind has to be found.

  • 25 Apr 2017 10:49
    Reply # 4777801 on 1306051

    Hi David (Webb) if I decide not to use my flagpole I will let you know. First I want to see if I can reinforce it or use it (or some of it) as part of a composite, because doing that might save me quite a few hundred dollars. I am still looking at options.

    Another possibly more expensive option might be to use about three metres of my flagpole to augment a 6m standard length of 6" tubing - if I could think of a way of making David Tyler's "casting polyurethane to fill the annular gap" method of joining up near the top. I think I only need about 8m total length for my mast (though not finalised yet) and doing it that way there might be enough in the flagpole to satisfy both our needs - I am guessing you won't be wanting much more than about 7m.

    If I can't get a definite answer for you by the end of May I could still keep an option open for you for when you get back in November. (I have figured out who you are now - I watched you sailing your cute little Gypsy Girl at McLeods Bay the other week.)

    PS I also have a smaller flagpole here which has been cut in half - I had intended to graft one of the halves onto a wooden base, to go into a tabernacle for an 18' Kestrel. I am not going ahead with that now. Maybe too short for your 7.5m project but I thought I would mention it as another possibility for you. You can get my contact details from the membership list and we can have a phone discussion about all this if you like.

  • 25 Apr 2017 05:18
    Reply # 4777654 on 1306051

    Hi Graeme,

    I am completing a light weight 7.5 meter drop keel junk rigged boat at the moment, and your flagpole may be ideal for her mast. I will be setting about 17 or 18 square meters of sail (175 to 200 sq ft) and she will weigh less than 1.5 tons, about half of your motor sailer. I will need to do some calculations to see if it is strong enough but it is about the size I was looking for. I live in Ruawai, Northland and could come and get it from Auckland before the end of May as I leave for Australia then and will not be back until November.

    Thanks, David. 

    Last modified: 25 Apr 2017 05:18 | Anonymous member
  • 25 Apr 2017 02:58
    Reply # 4777534 on 1306051

    (Sorry Scott, and David Webb, for crossing over your interesting discussion on conduits. Perhaps I should have tried to start a new thread. Haven't been on forum before.)

    Many thanks David Tyler for your response. Now I have some interesting alternatives to the standard alloy/wood composite idea which I was going to borrow from Fantail (and may yet still do.) I have another question, which is equally relevant to your outer sleeve suggestion and to both of the wood base ideas (ie inserting a plug, or grafting onto a wood base mast.) The question is, just eye-balling and without requesting time to be spent on calculations at this stage - how much of the upper mast do you think could be made from my flagpole section (either including the top tapered two metres, or just using a length of the parallel part of it)? I mean, in other words, how far up the deck do you think the reinforced (or replaced) section should need to go, before it could safely transition to just my aluminium flagpole with its 5" OD and its 3.6mm wall thickness?

    Whatever the answer is, I am thinking now it will probably be way too high up for the wooden plug idea to be practical - as you say, it would need to be a very loose fit and pumping epoxy unseen into unknown voids would worry me a bit. Also, by the way, if anything like 8.5" diameter is necessary at the heel for a wood base mast, then surely a 4" plug would not be strong enough anyway?

    So the question of how high up the mast one would need to go, relates mainly to the aluminium outer sleeve suggestion, or to the timber base mast suggestion - and asks: at what point up the mast would the scantlings of my light flagpole become sufficient for it to stand on its own?

    As an afterthought, I am expecting someone will tell me that a composite mast should be wood at the top, not aluminium at the top, because of the problem of yard gear chaffing into the aluminium. Am I being too pessimistic here?

  • 25 Apr 2017 02:27
    Reply # 4777505 on 1306051

    Hi Scott,

    I just used ordinary three quarter inch PVC electrical conduit. Once you fix the top and start to compress the conduit it will automatically pres itself against the wall of the mast and form a spiral. The more you compress the more spiral develops, I found that one spiral in the length of the mast was enough to hold it in place. At the bottom of the mast I installed a junction box just above the mast step, with a hole through the mast wall for the cables. Once the conduit was compressed I bolted the box to the mast wall. It was still working fine when we sold Arcadian last year. The cables were no problem to get through I just attached a small bundle of cloth to a fishing line which a blew through the conduit with a blast of air from the compressor, and then used the fishing line to pull the cables. I hope that it works for you as well as it did for me.


  • 24 Apr 2017 14:27
    Reply # 4771986 on 1530450
    David Webb wrote:I have never heard of anyone else using my method but it seems to work. In my masts I fixed the top of the conduit to the masthead, then compressed and twisted the conduit so that it was pressed against the outside wall of the mast in a spiral, then fixed it at the base. After two years of use no slapping or rattling of the conduits or wires, no additional weight either.

    David Webb posted this three years ago, but I'm only now getting to it.

    What type of conduit did you use, how strongly did you twist it, and what keeps it from untwisting back? Just the compression and capping at the ends? Seems like such a straightforward solution.

  • 24 Apr 2017 09:38
    Reply # 4771753 on 1306051

    You're right, Graeme, the flagpole is too light as it stands. But not much too light, and the upper half is about the right size. PJR gives a diameter of 8.5in/215mm for the sail area and LAP that you're planning for, and it does seem that making a wooden lower portion to mate with the aluminium at the point where a PJR-sized mast has decreased in diameter to 125mm would be one way to go. Another way would be to find an aluminium tube that would sleeve over the bottom portion of your flagpole. Easier said than done, but there are masts with such sleeves, at 5.5in outside diameter. I think you'd find it easier to buy a 6in tube, wedge your flagpole centrally within it, block off the lower end with modelling clay or other fluid-proofing substance, set it upright and pour in casting polyurethane to fill the annular gap. I used this method on a larger mast, as a way of increasing the length, and it turned out successfully.

    Of your other suggestions, I think the internal wooden plug would work. The split sleeve is hard to do under home workshop conditions, and likely to stick half-in. The wooden plug would have to be a very slack fit, or again it will get stuck half-in, so I would drill a small hole to inject more resin under pressure, after insertion.

    Last modified: 24 Apr 2017 09:47 | Anonymous member
  • 24 Apr 2017 04:00
    Reply # 4771436 on 1306051

    (First time on the technical forum and I have just spent half a day trying to find the most suitable thread for this question - like a dog on a ramble, so many irresistible other thread titles to explore....)

    I am planning the conversion of a small (8m) motorsailer, approximately 3 ton, looking at making a rig of something around 300 square feet, mast probably about 8m above deck.

    It so happens that I have in my possession a 12 metre flagpole - from the exit box upwards there is 10.5 m of usable length. I did not acquire this pole for this project (my intention was to cut it in half and use it on a much smaller boat.) It is mostly parallel with about 125mm (5") OD, wall thickness about 3.6mm - and the last couple of metres tapered to about 75mm (3").

    (Having trouble getting the exact wall thickness - it could be as much as 4mm, but for the sake of this discussion let us assume 3.6mm)

    I am not particularly wedded to trying to use this flagpole, but wondered if it was worth considering some way of reinforcing the lower portion if that would make it usable - or perhaps using part of it to make a composite mast.

    * Firstly, does anyone think it might be strong enough as-is? (Not ocean cruising, just coastal waters. Stepped in a tabernacle, 8m from heel to top including about 1m bury) 

    * If too light (as I think it probably is) could the lower portion of the mast be reinforced with heavy layers of glass fibre? Or, could a wooden plug be inserted into the bottom,say, 2 or 3 metres - greased with epoxy resin? Is it a practical proposition (in a home workshop) to slit the unused part and force it into the base as an inner sleeve?

    * Could part of it be grafted on to wood to make a composite mast? 

    While on the subject of composite masts, I have noted with interest the composite masts made from stock aluminium tubing, with the top part made from wood - and wondered if anyone has thought of doing it the other way round - that is, making the base mast with solid timber and the top part with much lighter aluminium. This question is slightly off the topic, but if I were to use any part of my flagpole for a composite mast then, being somewhat light, I would think my aluminium section would be better at the top than the bottom, and I thought the wooden base could then start from a square section which would fit rather more happily into a wooden tabernacle.)

    I hope these questions will come to the attention of some of the well-qualified and lateral-thinking people I see posting on these fora.

    Finally, if it is considered that my flagpole is too light to be of very much use on a boat this size, then let it be known to anyone near to Auckland, New Zealand, who might be considering converting a smaller vessel, that I paid $300 for it some time ago and would be open to seeing it used for such another, smaller vessel conversion.

       " ...there is nothing - absolutely nothing - half so much worth doing as simply messing about in junk-rigged boats" 
                                                               - the Chinese Water Rat

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