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Mast materials and Specifications

  • 03 Jan 2014 02:45
    Quote
    Reply # 1467048 on 1466863
    Anonymous member
    Robert Leask wrote:I"ve heard that excessive flexing can be a problem with fiberglass masts and he told me that with a moment of 6000 ft/lbs the masthead would deflect about 1 foot. (I'm not sure what the metric unit for that is) The ultimate failure load would be 54,000 ft/lbs with maximum deflection of 20%, which would amount to about 7 feet, more than 2 meters.

    Having never sailed with an unstayed mast I don't know how much flexing is normal, or acceptable. I'm estimating the maximum load on that mast under sail would be no more than 9000 ft/lbs which would deflect about 18 inches (500mm)
    Hi Robert,

    It's probably alright, however my experience to date with FRP masts has been that they are too flexible. That of cause does not mean they cannot be made stiffer, it's just the ones that I've experience of have been closer to fishing rods than masts.

    In general, as far as a free standing junk rig is concerned, stiffer is better (when the mast bends, all your control lines go slack, not good if you are using running LHP's etc) and also the smaller the diameter, the better as well, as the mast will then impose less drag on the unfavorable tack. That is, the tack in which the sail hangs away from the mast.

    Since your mast is only 90kg and they will do custom for you, I'd invest another 10 - 20kg in making it stiffer and possibly thiner as well.

    If your budget demands that you watch the pennies, take a look at a hybrid mast (wooden tapered top and aluminum bottom section) a tapered steel pole or even a wooden mast which in your part of the world should be very doable.
  • 02 Jan 2014 22:53
    Quote
    Reply # 1466890 on 1306051
    Deleted user
    Hi Peter in Canada.

    I'm yer Webmaster and am just posting to say 'Welcome' and that this is a good spot to post on this topic, and well done for not simply starting a new one! I took a quick look at your profile and see that you circumnavigated in a 37' gaffer and that you have now removed the 'old' rig and are going junk. Great decision, you'll love it.

    Regret I'm no expert on mast specs. and the site is a bit 'dead' at the moment, but I'm sure one of our experts will get back to you soon. My boat (left) is a Freedom 39 schooner with carbon fibre masts which don't deflect much at all. How grp would perform at the same sizes and diameters I don't know. I guess it would need a thicker layup. Another guess would be that Freedom went to carbon fiber because it was superior to glass.

    'Axial' means they wrap the glass around the mast in a spiral rather than laying it along the length of the mast. Our Freedom's masts are spiral wound. Suggest until the experts get back you take a look in Junk Information > Sails, Masts and Gear  and look at 'Masts - Figreglass - Tapered'. There are a couple of manufacturers there, plus you can download a spec. guide from Shakespeare.

    Hope that helps for now, and good luck with the conversion.
    Last modified: 02 Jan 2014 23:12 | Deleted user
  • 02 Jan 2014 22:18
    Quote
    Reply # 1466863 on 1306051
    Deleted user
    Hi all

    This is my first post here, hope I'm putting it in the right thread.

    I'm converting my 36' gaff rigger into a 3 masted junk, and I just obained a quote from a composite pole manufacturer in Colorado. My main mast will be about 35 feet (11.5m) from the deck, stepped in a tabernacle. The engineer told me their 35' pole would weigh about 200 lbs (90kg), have a top diameter of 7.1"  (180mm) and at the bottom about 11.5" (290mm). I"ve heard that excessive flexing can be a problem with fiberglass masts and he told me that with a moment of 6000 ft/lbs the masthead would deflect about 1 foot. (I'm not sure what the metric unit for that is) The ultimate failure load would be 54,000 ft/lbs with maximum deflection of 20%, which would amount to about 7 feet, more than 2 meters.

    Having never sailed with an unstayed mast I don't know how much flexing is normal, or acceptable. I'm estimating the maximum load on that mast under sail would be no more than 9000 ft/lbs which would deflect about 18 inches (500mm)

    That sounds reasonable to me, and the price is also reasonable compared with carbon fibre. They use expoxy resin in their layup and their winding process gives more longitudinal fibre than other manufacturers, I'm told. They also do custom orders and can add more axial wrapping (whatever that means) to increase the stiffness and strength.

    Does it sound viable to an experienced junk rigger?
  • 20 Oct 2013 20:46
    Quote
    Reply # 1417369 on 1417199
    Deleted user
    Peter Scandling wrote:

    Adrian doesn't mention reducing the wall thickness, and in a later email he confirmed they use 6082 t6. 

    Peter

    Sounds as if they may have given up making spun (?) tapered masts then. You might want to ask that question and if the answer is yes, ask why :-) Sounds very much like the method Atlantic Spars used for Jonathan's.
  • 20 Oct 2013 16:08
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    Reply # 1417201 on 1306051
    Anonymous member

    Having just read Jonathon's article about his OSTAR it would be interesting to find out from Atlantic spars how they construct theirs. 

    I have contacted companies like NEDAL in the Netherlands and they can produce suitable one piece tubes to any spec..... however there is a minimum order of 10 :-(

    Peter
  • 20 Oct 2013 16:05
    Quote
    Reply # 1417199 on 1306051
    Anonymous member

    Brian

     

    I had a conversation with Needlespars about a mast for Mariposa.  Below is their response:

    Hi Peter,
     
    We would make this out of 1/4 inch wall Tube with a 5” Diameter x 5m length for the bottom, a 2.5m x 4.5” Diameter tube for the middle and a 4” Diameter x 1.5m length for the top.
     
    You would then have a 2m internal sleeve fitted at deck level, 1/3 below and 2/3 above the deck point..
     
    If we were to make this complete and ready for collection/delivery it would be £1370 plus VAT
     
    If we were to cut, machine and anodise the tube ready for final gluing and pinning, it would be £1074 plus VAT.
     
    If we were to supply just the bare tubes cut to length, it would be £624 plus VAT.
     
    I hope this all makes sense.
     
    Best Regards
     
    Adrian

    Adrian doesn't mention reducing the wall thickness, and in a later email he confirmed they use 6082 t6. 

    Peter
  • 20 Oct 2013 15:04
    Quote
    Reply # 1417169 on 1306051
    Deleted user
    It's a shame no-one from Needlespar can join in these discussions, and also that those who obviously liaised with them for many years don't join in. Perhaps Needlespar could be asked to respond?

    As one who had Needlespar masts on our Sunbird 32 for 30 years, that is until we sold her, the only time I was ever concerned about them was when sailing hard to windward in rough seas or motoring in similar conditions. The bending of the foremast under sail was controllable by prudent reefing. The whipping of the foremast when powering into wind over tide conditions was disconcerting but never a problem. Maybe we sold her just in time! I seem to recall that Sunbirds increased the size of the foremast, after Sabra's foremast came down in the Atlantic - see Newsletter 26.

    I had a discussion about Needlespar masts a few days ago with a member who rarely posts, but he was wondering how their masts are/were produced, ie does the tapering somehow preserve the wall thickness towards the mast top, or is the material squeezed to produce the taper making the material thinner towards the top? And does it need to be the same wall thickness throughout? Anyone know?

    Ah, their website explains www.hawkmarineproducts.com

    Last modified: 02 Jan 2014 23:10 | Deleted user
  • 20 Oct 2013 12:50
    Quote
    Reply # 1417128 on 1306051
    Deleted user
    Rather late to this, but it is the right thread so didn't want to start a new one.

    China Girl has a 5.5" (137mm) diameter tapered aluminium mast with 6mm wall thickness, 8.5m LAP from needlespar. It appears to be sleeved with a 6mm wall tube inside for the first 1.5m or so. On a 5 ton boat with a 2.6m beam this seems woefully under specified.

    Doesn't seem to flex much in normal usage, but in returning from France this year I had a cruising chute hoisted to the mast head, and left it up a little too long - as the wind rose a little the mast was bending like a fishing rod - haven't moved so fast in a long time!

    The common factor here appears to be Needlespar. Are they under specifying aluminium sections even for coastal cruising boats?
  • 04 Jun 2013 12:13
    Quote
    Reply # 1308886 on 1306051
    Deleted user
    Welcome back to the land of the wired & connected David.

    re: sunbird boat-  I dont believe its a 3-1/2" mast, more like someone hung the sails on the VHF aerial by mistake..
    Last modified: 04 Jun 2013 12:13 | Deleted user
  • 04 Jun 2013 07:46
    Quote
    Reply # 1308823 on 1306051
    Anonymous member (Administrator)

                                                                       Stavanger, Tuesday

    David, thanks for coming ashore (..er, onboard...) again and giving us a hand here. I basically use the methods you describe to calculate the section of a mast. The challenge is to find a sensible safety factor. The additional forces caused by whipping in offshore conditions must be considered, but I am not sure how much it counts. The slimness of a mast - LAP/ diameter is worth thinking of and my hunch is that the very slim Needlespar masts are more vulnerable in rough offshore seas than tubbier ones, even if the skipper reefs the sails conservatively. In other words, offshore cruisers’ and racers’ masts must be made with a bigger safety factor over the plain static stress of heeling. Right?

    Arne

    PS: I have high hopes for my new hybrid mast for Frøken Sørensen. This building method surely has been the easiest and cheapest way to get a mast for her.

    Last modified: 04 Jun 2013 13:15 | Anonymous member (Administrator)
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