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Mast Step and Partners

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  • 11 Sep 2017 01:10
    Quote
    Reply # 5073569 on 534932
    Anonymous member (Administrator)

    Thanks David - and for the benefit of anyone in New Zealand, here is a reply to my inquiry to the Hamilton agent for PMC:

    Hi Graeme,

    The hardest PMC we have in stock is PMC-780 available here:

    https://www.fibreglassshop.co.nz/products/pmc-744-urethane-rubber-for-strong-durable-molds?variant=23511667969

    Please note there is a release agent built into this product which may or may not be an issue for you. Check the information sheet for more information.

    If you’d like to get PMC-790, we make an order to Smooth-On once every 4-6 weeks, with a lead time of another 4-6 weeks. The minimum size order we can do for a product we don’t stock on our shelves is a 10.89 kg kit (or 4 x 1.36 kg kits), very roughly $300-$400.

    Probably about the same price as Spartite which I believe is available in Auckland.


    Last modified: 11 Sep 2017 01:16 | Anonymous member (Administrator)
  • 09 Sep 2017 07:28
    Quote
    Reply # 5071541 on 534932
    Anonymous member

    I've used genuine Spartite to cure the grinding noises coming from an alloy mast in an alloy step, and I can't say that it was very different from the industrial mouldmaking and prototype making pourable polyurethane that I've used for partners and filling annular gaps. In Canada, I used Smooth-on brand, TASK series, and in the UK, I used a similar product from Easy Composites. Don't get too hung up on the tech specs. We're not putting a great deal of pressure on the polyuethane, and I venture to suggest that almost any of them will do the job. Having said that, you may as well play safe and get the strongest/most rigid one. 
  • 08 Sep 2017 22:50
    Quote
    Reply # 5071124 on 534932
    Anonymous member (Administrator)

    Barry S., some years ago wrote:

    "We did not use Spartite because it is expensive, and it is also reported to be too soft for a freestanding mast.  Instead we used a harder PU rubber compound called PMC-790.

    You can read more about it on this thread from the Freedom owners forum. http://freedomyachts.org/viewtopic.php?f=9&t=47

    I did my homework....but haven't passed all the tests yet: The masts have been up for less than six months.  They haven't fallen down or leaked (We used additional bedding above and they are clamped in above and below, so there is no way the wedge could work out of the partners).  But no sailing to date (still working on sails), and no attemps to remove the masts either."


    Can Barry (or anyone else) report back on the performance of PMC-790 as an alternative to Spartite? I notice Paul T. also commented on this thread.

    I have not yet found a supplier for PMC-790 in New Zealand, but the Fibreglass Shop in Hamilton supplies PMC-744 and may possibly be a source for PMC-790 - they have not got back to me yet.

    The tech specs for Spartite are:

    Technical Specifications Spartite 2000
    Mix Ratio by weight or volume 100/25
    Mixed viscosity @ 25°C, cps 2,500
    Pot Life @ 25°C 8-14 min
    Cure @ 25°C (days before sailing) 3 days
    Color Midnight Blue
    Shore Hardness 55-60 D
    Tensile Technical Specifications, psi 4,000
    Ultimate Elongation, % 200
    Tear Strength (Graves), pli 600
    Compressive Modulus, psi 55,000
    Linear Shrinkage, in./in. .001
    Izod Impact, notched, ft. lbs./in. 9.5



    PMC-744 claims 

    Specific Gravity 1.01 g/cc
    Specific Volume 27.5 cu. in./lb.
    Pot Life 15 minutes
    Cure Time 16 hours
    Color Beige
    Shore Hardness 44 A
    Tensile Strength 300 psi
    100% Modulus 90 psi
    Elongation @ Break 400 %
    Shrinkage < .001 in. / in.
    Die C Tear Strength 90 pli


    PMC-790 (not sure yet if is is available in New Zealand) claims 

    Specific Gravity 1.07 g/cc
    Specific Volume 25.9 cu. in./lb.
    Pot Life 20 minutes
    Cure Time 48 hours
    Color Clear Amber
    Shore Hardness 90 A
    Tensile Strength >2000 psi
    100% Modulus 640 psi
    Elongation @ Break 550 %
    Shrinkage <.001 in. / in.
    Die C Tear Strength 300 pli
    Mixed Viscosity 3,000 cps

    I am not sure how to compare the above.

    Anyone with engineering knowledge who can comment on the possibility of a reasonable priced alternative to Spartite?

    I am thinking here not just about an alternative to wedges at the partners - but also suitable stuff to span annuar gaps of up to 1cm to enable joins in a composite alloy/alloy and alloy/wood spar. David T has reported successfully using pourable urethane - but I am not sure what the product name was.




    Last modified: 08 Sep 2017 22:56 | Anonymous member (Administrator)
  • 26 Mar 2011 04:52
    Quote
    Reply # 553503 on 550223
    Anonymous member
    Robert Groves wrote: ...our boots were some plastic sheeting and lots of duct tape. Keeps out the water and lasts forever. If the wedges get loose a tap with the mallet, without removing the tape and plastic, works just fine. A little abrasion is taped over. The subrella kept the tape and plastic from deteriorating at all for five years on the main mast until we pulled the masts this passed fall. Disguised by the sunbrella boot the installation is functional professional looking.
    I have just bought an interesting mast boot called a Dektite, from a plumber's supplier, designed for sealing pipes where they come through the roof.  It cost $61 dollars Aus but I may not have bought it if I'd read Robert's comments first!  Nonetheless the Dektite, secured with two hose clamps, will be very easy to life to inspect the wedges.  I have also decided to use soft timber wedges and am thinking of smearing the epoxy primed steel partners with lanolin grease to protect the paint a bit as I gingerly tap them in.  Any comments about greasing timber wedges?
  • 23 Mar 2011 00:12
    Quote
    Reply # 551439 on 551247
    Anonymous member
    Annie Hill wrote: Very true, Paul, but the water may still find a way between the two flanges unless they are put down on lots of flexible gunk.  Which I assume they will be?

    Indeed my lady, you can be sure of it.
  • 22 Mar 2011 19:20
    Quote
    Reply # 551247 on 534932
    Anonymous member
    Very true, Paul, but the water may still find a way between the two flanges unless they are put down on lots of flexible gunk.  Which I assume they will be?
  • 22 Mar 2011 04:53
    Quote
    Reply # 550851 on 534932
    Anonymous member
    On Aphrodite (and also on La Chica, my own boat) I have used flanges on the mast and also on the partners and the two are just bolted together. Simple, neat and quick. Saves an awful amount of mucking around with bits of wood, duct tape et al... and guaranteed your mast will not be going anywhere it shouldn't.

    Of cause using steel masts on a steel boat also helps to simplify things somewhat :-). If you want to see what it looks like, I have put a few Aphrodite photos up. You can see them here Aphrodite Photos
  • 22 Mar 2011 00:20
    Quote
    Reply # 550718 on 550223
    Anonymous member
    Robert Groves wrote: The mast boots on Easy Go are a version of that found in PJR. They are made of sunbrella. They are placed on the mast inside out and a cinching knot pulls them tight. They are then rolled correct side out and fastened around the ring at the top of the partners. Works really well, looks great but doesn't keep all the water out. Prior to making these covers our boots were some plastic sheeting and lots of duct tape. Keeps out the water and lasts forever. If the wedges get loose a tap with the mallet, without removing the tape and plastic, works just fine. A little abrasion is taped over. The subrella kept the tape and plastic from deteriorating at all for five years on the main mast until we pulled the masts this passed fall. Disguised by the sunbrella boot the installation is functional professional looking.
    I use exactly the same on Tystie - 
    An inner coat of waterproof material, glued and sealed. Doesn't matter what it looks like as long as it's watertight.
    An outer coat of acrylic canvas to keep the UV off. Doesn't matter that it isn't watertight as long as it looks good.
  • 21 Mar 2011 22:34
    Quote
    Reply # 550648 on 534932
    Anonymous member
    Yes, David, and in a perfect world I would have done as suggested.  However, the world is imperfect and I had to work around what was available and affordable.  The tapered partners were going to cost even more.

    But I am (fortunately) an optimist and am sure that shaping, adding bits, nailing addtions and/or sticky stuff will achieve the desired end.  And if I can find some sort of cheap Spartite (still looking!) I can easily get my hand up between the mast and the partners to smear on some tallow.  Occasionally there are advantages to child-sized mitts.

    I shall take the advice of Arne and Robert and start with wedges and proceed from there.  There is enough choppy water around Tasman Bay to give things a thorough shake up early in the piece.

    At present I am playing with boom, battens and yard.

    Thanks for all the ideas and advice.  I do think, on odds, that the solid mast collar along Gary's lines is probably the simplest and most effective over all.
  • 21 Mar 2011 13:02
    Quote
    Reply # 550223 on 534932
    Deleted user
    The mast boots on Easy Go are a version of that found in PJR. They are made of sunbrella. They are placed on the mast inside out and a cinching knot pulls them tight. They are then rolled correct side out and fastened around the ring at the top of the partners. Works really well, looks great but doesn't keep all the water out. Prior to making these covers our boots were some plastic sheeting and lots of duct tape. Keeps out the water and lasts forever. If the wedges get loose a tap with the mallet, without removing the tape and plastic, works just fine. A little abrasion is taped over. The subrella kept the tape and plastic from deteriorating at all for five years on the main mast until we pulled the masts this passed fall. Disguised by the sunbrella boot the installation is functional professional looking.
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