Mast materials and Specifications

  • 10 Sep 2017 02:07
    Reply # 5072529 on 5071264
    Paul Thompson wrote: To the best of my knowledge all single part polyurethanes are moisture cured. That is why they set out of the tube and why they eventually harden inside the tube as well once the seal has been broken.
    You are quite correct, Paul.  However, as Simsons is not a single part polyurethane glue, the comment is irrelevant!
  • 09 Sep 2017 16:41
    Reply # 5071915 on 1306051

    Thanks David.

    For the moment I will follow the simpler idea of extending the height of the mast by fibreglass sleeving the lower part of the flagpole and just fitting it into the top of the 6m pole.

    The 1m heel plug extension. The reason was, it was a matter of getting the required 11m over all, without having to use the flag pole for more of an extension than 4m, as it does seem a little slender.

    I could have used more of the flagpole and less of an extended heel plug. But the heel plug being a solid 142mm diameter where it fits into the 6m pole – thicker than the mast would be in this area if it were tapered below the partners in the usual way – I thought it was the better option.

    Option 1: 

    (a) 1.5m heel plug with 0.5m bury in the 6m pole, gives 1.0m extension at the bottom

    (b)  6m pole

    (c)  4.5m flag pole with 0.5m bury in the 6m pole, gives 4.0m extension at the top

    Total length of spar (a) + (b) + (c) = 11m


    Option 2  

    (a) 1.0m heel plug with 0.5m bury in the 6m pole, gives 0.5m extension at the bottom

    (b)  6m pole

    (c) 5.0m flagpole with 0.5m bury in the 6m pole, gives 4.5m extension at the top

     Total length of spar (a) + (b) + (c) = 11m


    The main mast section is 152mm in diameter with 5mm wall thickness.

    The flag pole is only 3mm wall thickness.

    The heel plug would be solid timber, 142mm diameter where it fits inside the 6m pole.

    The partners are 1.8m above the heel.

    Extending the solid heel plug at the bottom seemed to me a safer bet than extending the slender flagpole at the top.

    I have not explained it very well, but am I mistaken here?

    Why is Option 2 (extended heel plug reduced to 0.5m) better than Option 1?


    Last modified: 09 Sep 2017 16:50 | Anonymous member
  • 09 Sep 2017 07:54
    Reply # 5071561 on 1306051

    Graeme, I'm a little uneasy about the length of the "extended heel plug", and wonder whether it ought to be reduced in length to 0.5m.

    Both methods of adapting the flagpole topmast will work, certainly, and I think it comes down to which is easiest to do, overall. Though if I were considering  the wooden version, I'd just make the whole topmast in wood and forget the flagpole.

  • 09 Sep 2017 07:37
    Reply # 5071543 on 5071102
    Annie Hill wrote:
    David Tyler wrote:

    Just one comment: Simsons needs moisture to cure it, so don't epoxy coat the douglas fir, and dampen the inside of the top of the main tube. 


    I don't think that you're correct there, David. I have used Simpsons Marine Glue fairly extensively and don't recall reading anything about moisture curing. I can assure you that I coated Fantail's mast thoroughly with epoxy before setting it in to the tube. The mast rotated slightly in its step before I fitted the rigging screw, but there was no sign of any movement between the topmast and alloy tube.
    If you make a long joint with impervious surfaces and Simsons, it will eventually cure right through, but the process might take weeks or months rather than days. The cure must start at the ends exposed to atmospheric moisture and work its way along. As Paul says, it's just what happens when you've  broken the seal on a tube of Simsons - the cure starts at the nozzle and works its way inwards. However, where the joint is short, as with a heel plug, it's possible to coat with epoxy, so long as load is not applied too soon.
  • 09 Sep 2017 01:04
    Reply # 5071264 on 5071102
    Annie Hill wrote:
    David Tyler wrote:

    Just one comment: Simsons needs moisture to cure it, so don't epoxy coat the douglas fir, and dampen the inside of the top of the main tube. 


    I don't think that you're correct there, David. I have used Simpsons Marine Glue fairly extensively and don't recall reading anything about moisture curing. I can assure you that I coated Fantail's mast thoroughly with epoxy before setting it in to the tube. The mast rotated slightly in its step before I fitted the rigging screw, but there was no sign of any movement between the topmast and alloy tube.
    To the best of my knowledge all single part polyurethanes are moisture cured. That is why they set out of the tube and why they eventually harden inside the tube as well once the seal has been broken.
  • 08 Sep 2017 23:56
    Reply # 5071248 on 1306051

    I have another question for you David.

    As an alternative to wrapping the smaller diameter component in fibreglass (to a thickness of 1cm) - and perhaps to reduce any issues of flexibility and/or epoxy bond with alloy – what would you think about a short hollow spar component made of douglas fir – a loose fit in the standard alloy tube at one end, and a loose fit in the flag pole at the other – tapered to transition the two diameters. I could make the hollow spar component without too much difficulty, being less than 1.5 metres in length – and I think I have found a wood turner who could swing that length and shape everything nicely.


    This had been my original idea until Annie suggested the simpler idea of just building up the diameter of the flagpole with fibreglass.

    I have an idea both methods would work in practice – the wood detail seems a little more work, but I don’t mind that if it is thought to be a better detail. (It puts about an extra 6 -7 kg up there, though, compared with just overlapping the tubes and building with fibreglass.)


    Last modified: 09 Sep 2017 07:03 | Anonymous member
  • 08 Sep 2017 22:15
    Reply # 5071102 on 5069880
    David Tyler wrote:

    Just one comment: Simsons needs moisture to cure it, so don't epoxy coat the douglas fir, and dampen the inside of the top of the main tube. 


    I don't think that you're correct there, David. I have used Simsons Marine Glue fairly extensively and don't recall reading anything about moisture curing. I can assure you that I coated Fantail's mast thoroughly with epoxy before setting it in to the tube. The mast rotated slightly in its step before I fitted the rigging screw, but there was no sign of any movement between the topmast and alloy tube.
    Last modified: 10 Sep 2017 03:16 | Anonymous member
  • 08 Sep 2017 09:11
    Reply # 5069880 on 1306051

    Just one comment: Simsons needs moisture to cure it, so don't epoxy coat the douglas fir, and dampen the inside of the top of the main tube. 

  • 07 Sep 2017 09:52
    Reply # 5067036 on 1306051

    Thanks for all the advice so far.

    After much thought and some changes of plan, I think the following is the direction I will take, and I would like to run this proposal past the experts, hoping to be informed if there are any bugs I have overlooked.

    1. The mast will be 11m over all, keel stepped, 9.2m above partners.

    2. Basic mast will be a standard 6m length of alloy tube, .152mm in diamater and 5mm wall thickness. (6.251 kg/m = 37.5kg)

    3. It will be augmented at the top by 4.5m cut from a tapered aluminium flagpole which I have, the parallel part being 120mm diameter and wall thickness (as measured) 3.8mm. (Estimated 3.85 kg/m = 17.33kg.)   0.5m of the flagpole will be inserted into the standard aluminium pole, thus augmenting the length by a nett 4m.

    4. The mast will also be augmented at the base by a 1.4m length of 6" x 6" square section solid douglas fir, (estimated weight 17kg). The top .4m of this section will be shaped round and inserted into the base of the standard aluminium pole, thus adding 1 metre of length at the base.

    5. The detail of the join at the top section of the mast will be as follows: the lower part of the flagpole will be sleeved with a layer of glass-reinforced epoxy, to a thickness of about 1cm, to make it a loose fit into the standard aluminium pole. The sheathed part will be prepared with the etch primer provided by West system for bonding epoxy to aluminium. This sheath will continue sufficiently far up the flagpole to allow the necessary taper to transit the two diameters, and additional expoxy filler will be added to fair out the remaining 5mm shoulder. The flagpole with its sheathed lower end will be fitted into the standard aluminium pole and fastened with flexible adhesive (eg Simpsons.)

    6. Likewise the wooden base piece will be given a coating of  epoxy resin, then inserted into the lower part of the standard aluminium pole and fastened with Simpsons or similar.

    The result will be an 11m mast weighing just over 70 kg.

    1m wood, 6m pole, 4m tapered flagpole

    Click on diagram below for further details.


    To compare with the existing bermudan deck-stepped mast - the part of the new mast which is above the partners will be 9.2m, should weigh less than 50kg and the centre of gravity of that part should be about 4.11m above the partners.

    This compares more than favourably with the original deck-stepped 8.95m untapered bermudan mast which is estimated to weigh more than 56 kg (not counting spreaders and rigging) and whose centre of gravity is about 4.6m above the partners. (It is currently stepped on the aft cabin top, some .1m higher than where the new mast partner will be.)

    The top section seems a bit light to me, but I think I should make use of what I have.

    The biggest unknown will be, as David has pointed out, the discontinuity with respect to flexing at the reinforced part of the topmast. I can only assume that it will be not very different to the detail of timber topmast (as in Fantail) which seems to have proved itself satisfactory in practice. How well epoxy will stick to aluminium under these circumstances, and the efficacy of West Systems' aluminium etch primer will be interesting to find out too. 

    Any comments would be gratefully accepted.


    Last modified: 07 Sep 2017 21:21 | Anonymous member
  • 26 Apr 2017 14:57
    Reply # 4780441 on 4777822
    Graeme Kenyon wrote:

    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.


    This is not something that I've had to attempt, so I can't offer you anything tried and tested, as I usually aim to do. I can only say that as an unstayed mast cannot be totally rigid, so any fairing should not be totally rigid either. That's why I use a polyurethane sealant  [I can recommend Simsons, as you're in NZ] to assemble a wooden topmast into a tube, for a little bit of flexibility.
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