Can I build 50' free-standing masts out of composite?

Discussion in 'Fiberglass and Composite Boat Building' started by Seafarer24, Aug 15, 2011.

  1. BATAAN
    Joined: Apr 2010
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    BATAAN Senior Member

    I'm also taking a shot in the dark that few have deeply researched or spent many years sailing the CL and rely on others to tell them how it works.
     
  2. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    I've been researching the junk rig for at least 5 years. Rigging a Freedom 40 like this is not a new idea to me, but I thought I would sail around on my current boat for a while (5-10 years) before I'd ever find a F40 that I could afford.

    I've got the current owner considering an even trade for my boat, which is very close to ready-to-sail and comes with a host of gear that this F40 doesn't have: a diesel generator, fresh-water maker, mast and sails, enclosed head with shower....

    I went aboard this morning and measured the ID of the mast collars, and they are a whopping 11.375". I figure the mast is probably 11.25" with a .0625" space all the way around to be shimmed? The mainmast was 4' from step to partners and I couldn't measure the mizzen bury but am assuming it is similar. I recall hull #1 had the mizzen stepped on the forward end of the centerboard trunk and the masts were interchangeable. I completely forgot to measure the distance between the masts!

    This boat originally had aluminum masts which cracked and were replaced with carbon fiber under warranty. These were torn off when a bridge tender dropped a bridge on the boat, and for some reason the owner never replaced them. Probably because he was 80-something years old and using the boat as a trawler by that point. He had sailed the boat from California, all along the west coast and South America, through the Panama Canal and the Caribbean. He then went up the east coast at least as far as the TPI plant to get the masts replaced before returning to FL where he eventually sold it to the marine mechanic that currently owns it but is not at all interested in sailboats.

    So, due to the ID of the collar I suspect I am back to building a hollow wooden mast. I doubt that the 10" OD light poles would be strong enough after all.
     
  3. Eric Sponberg
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    Eric Sponberg Senior Member

    No, your initial assumption is correct, 10" aluminum tapered tubes were the original mast sizes, although as I said, I am unsure of the wall thickness. The partner wedges were very thick rubber collars that fit around each mast. The mizzen bury is about 6.5', and the mizzen is stepped on top of the centerboard trunk. The distance between the masts, center to center, is 20' 10". They are raked aft slightly.

    Eric
     
  4. Steve W
    Joined: Jul 2004
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    Steve W Senior Member

    The reason the owner never replaced the carbon masts was probably the between collecting a large insurance settlement for new carbon ones and still having the boat to sell sans masts he probably ended up with way more $$ than he could have sold the complete boat for.
    Steve.
     
  5. captrhoa
    Joined: Jun 2012
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    Location: florida

    captrhoa New Member

    carbon mast

    Yes, it is possible to build a carbon mast at home, but it must be done correctly. I am presently building a 60' mast with a total cost of $12,000 for a blue water race boat.
     
  6. Eric Sponberg
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    Eric Sponberg Senior Member

    Whereabouts in Florida are you located? Do you have any details of the mast design that you are building?

    Eric
     
  7. rob denney
    Joined: Feb 2005
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    rob denney Senior Member

    Home built masts are simple, and low cost.

    The mast tube on the 15m in the video (http://www.youtube.com/watch?v=8chR6DAFjGA) weighs 120 kgs: 50 kgs of carbon ($50 per kg), 18 kgs of glass ($10/kg) and 52 kgs of resin ($18/kg).
    Materials cost $3,700. About another $1,000 for the consumables, bearings and all the fittings. Less than 100 hours work for the tube, using simple moulds and a vacuum bag.
    Engineering for this mast was $233 ($700 split between 3 masts). Plans to build it cost $500.

    rob
     
  8. Bendigonian
    Joined: Nov 2011
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    Bendigonian Junior Member

    Bataan noted that:
    "These loads can form a rhythm in the wrong sea conditions and make the mast whip enough to overload it and break it off at the partner if unstayed, but are usually countered by taking the halyard aft and to windward to stop the 'pumping'. I had a fully set Chinese rig disappear over the bow once (not on my present boat) due to this effect and it was most dramatic."
    I've always considered this to be a problem (minor), with CF free standing masts, and one that is exacerbated when motoring. Under sail the mast is under continuous strain and, to take a simplistic view, all the cracks that formed when it first came under load, close up, (on the compression side anyway), and all is tickety-boo. When motoring, and even by report at anchor, the mast tends to whip back and forth. Into a trough, whip forward, out of the trough whip back.
    Not much maybe, but possibly enough to increase the crack size of any initial and minor fatigue fractures, (see p78 of Eric's Design and Engineering Aspects of Free-standing Masts and Wingmasts..invaluable and unique Thank you Eric). This carries on until the Griffith crack length is reached and overboard she goes. Read the `Crack and Dislocations` chapter of J.E.Gordons 'The Science of Strong Materials" enormously erudite and humorous, and a damn good read for all neophytes in design or materials sciences. After reading Professor Gordon's books you start to wonder how any boats manage to hold together long enough to cross an ocean!
    This is all supposition and I don't have the time, or the maths, to prove it. But just go and look at the remains of Kurt Hughes' Sarabi's CF aeorig that broke at the partners while motoring. Her original builder/ owners also mentioned that she felt a bit weird and jerky when motoring. In the archives somewhere I've also got some pictures of the early Freedom CF masts that failed. They looked like pure delamination whereas Sarabi's mast is thought to be from an insufficient wall thickness. (Not Mr Hughes' doing, I must stress, but probably a manufacturing flaw. Sarabi is a beautiful design and I only wish I had the odd million or so when she came up for sale a few years ago.
    So, if you've got a CF free standing mast, then it may pay to take Bataan's advice and strap it down.
     
    Last edited: Jul 8, 2017
  9. Nick.K
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    Nick.K Senior Member

    Friends, Eamon and Becky built their boat themselves and fitted it with free standing lamp pole masts and junk rig. They lived on board for some years cruising from Ireland to Greece and back and recently set off again. So far, I don't think there have been any major issues with the rig. Wayward.jpg
     
  10. Bendigonian
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    Bendigonian Junior Member

    Yep, trees are actually designed by the Creator to whip back and forth, (don't see too many living trees snapped off at the partners), and the junk rig is designed by generations of inscrutable Chinese to depower at high wind speeds by bellying. Professor Gordon mentions this in his other book, 'Structures, or why things don't fall down', with some design thoughts on trees' cellular structure. A fascinating book, worth every cent. His first love was always wood, and he helped design the Mosquito, one of the most successful of all wooden planes, as well as emergency inflatable bomber life rafts, which gave him an increased admiration for the A-frames used on Egyptian reed boats.
    Lamp posts are probably fine on a ketch rig like your friend's junk, where the mast height can be kept down, (and damn cheap too. At least they're at sea, whereas high-tech dreamers like me are still land-locked), but if you went much higher, on a schooner rig say, you'd end up with something that wouldn't look out of place on the Victory.:)
    The problem with wood is longitudinal cracking, particularly as it ages and loses moisture content. It surprised me that a tree has only a small ring of living cells, and most of the interior is dead wood. Hence all the 'fishing' of masts and yards that abound in every Patrick O'Brian book. Fishing was the practice of binding a second spar to a first when it cracked longitudinally at sea, which used to happen routinely if the masts or spars were called upon to bend in a blow.
    What's needed is some form of cheap natural fibre structure that doesn't lose moisture content, perhaps with crack resisting stiffeners built in....And we come back to the Chinese junks with their bamboo masts.
     
  11. Nick.K
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    Nick.K Senior Member

    Steel poles not wood.
     
  12. gonzo
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    gonzo Senior Member

    Does the mast need to be carbon or aluminum? You could buy a couple of pine power line posts and plane them to the required diameter.
     

  13. Chuck Losness
    Joined: Apr 2008
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    Chuck Losness Senior Member

    It all gets back to the loads on the mast. This is the starting point. Eric has graciously shared his knowledge on the design of free standing masts. Search for all of his posts and you will be able to put it all together. You will need to create a spreadsheet to show the loads along the mast at one foot intervals. Then you can plug in different materials and sizes to see if the mast is strong enough to handle the loads. Next is the weight calc's. I found it to be a very challenging intellectual exercise. I often dream about having a 30 foot cat ketch. Then reality of my finances rears its ugly head and shatters the dream. Oh well. Maybe I will win the lotto.
     
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