How large can you home-build a free-standing mast?

Discussion in 'Sailboats' started by Seafarer24, Mar 6, 2008.

  1. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    In my never-ending search for "the" boat to go cruising in, I've stumbled across an interesting opportunity.

    This 1981 Cheoy Lee 43 hull (reportedly, with engine) has a fire-damaged interior. I'll be looking at it tomorrow but the person on the phone said it was pretty much gutted and has no mast or sails.
    [​IMG]

    I've determined that I really want to have free-standing masts on my next boat. I've vaguely considered purchasing this hull and rebuilding the boat as a cat-ketch...

    I doubt I can afford to have carbon-fiber masts built, but I could probably handle building my own from a wood/fiberglass (perhaps use some foam as well?) composite. Each should be able to hold a ~500 sq. ft. sail (square-top & fully battened). Most likely I'll go with wishbone booms. I would plan to run a large mizzen staysail (~600sq.ft.), with running backstays if necessary.

    Can composite masts be built large enough and strong enough
     
  2. marshmat
    Joined: Apr 2005
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    Location: Ontario

    marshmat Senior Member

    Yes, they can.
    That may be a different story.
    I'll mention two points:
    - Engineering a freestanding mast would be very different from engineering a conventional stayed mast; the loads are completely different, the support conditions are completely different, and in the case of a composite mast, you generally end up with a non-uniform cross section and non-uniform material properties (directional fibres, different thicknesses/types, etc). This is engineer's hell (or engineer's paradise, depending who's paying whom).
    - Manufacturing the thing will require excellent craftsmanship, thorough quality control and several experienced hands. I've designed and built some very sophisticated carbon semi-monocoque structures and bodies for trans-continental solar race cars, yet I wouldn't even think about touching this mast build without an experienced mast builder to guide the fabrication process. Experience is key.

    Fire damage, total rebuild? Sounds like you've got your project cut out for you. Best of luck!
     
  3. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    *Most likely* I won't go through with a project this big. However, I don't always show the best judgement. I'm pretty certain it was designed as a motor-sailor, which means it motors like a sail-boat and sails like a motor-boat. Seeing it in person tomorrow will give me a better idea of just what's in store.

    I was thinking, for a free-standing composite mast:
    Central X-section with foam filling the two sides of the X, or even two side and the front of the X, with double-diagonal wooden veneers and a light exterior layer of 'glass? It could be built slightly larger around than is typical...

    I suppose I should shoot the Gudgeon Brothers an e-mail...
     
  4. Omeron
    Joined: Feb 2007
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    Omeron Senior Member

    Just curious...
    Would a fire big enough to destroy the interior would also damage the deck and perhaps the hull as well? I mean, the structure would be there, but would the heat cause damage to the composition of the resin?
     
  5. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    It's possible, that's why I'm going to check the boat out in person today.

    Typically, when I go to look at a boat I bring along a digital camera and a notepad. I take pictures of everything and jot down notes on whatever peaks my interest. Then, I can go back through the notes later and have the pictures for reference.
     
  6. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    The biggest mast I've built was a 47' stick for a cutter, using the birdsmouth method. It was stayed, but could have been dimensioned to be free standing. The Choy Lee 43 sailed pretty well, being an over engined, fairly burdened sailing hull, providing some motorsailing possibilities.

    She came with a pilothouse and was a scaled down version of some of their larger motorsailers (the 63 most notably). She carried twin steering stations, her fat but permitted an aft stateroom and the deck structures where pretty tall. I also remember a fairly sizeable engine compartment which housed a 85 - 90 HP diesel.

    The picture above doesn't appear to be the Choy Lee 43 hull, which had more forward ports and also a few in the aft cabin.
     
  7. rob denney
    Joined: Feb 2005
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    Location: Australia

    rob denney Senior Member

    I've determined that I really want to have free-standing masts on my next boat. I've vaguely considered purchasing this hull and rebuilding the boat as a cat-ketch...

    I doubt I can afford to have carbon-fiber masts built, but I could probably handle building my own from a wood/fiberglass (perhaps use some foam as well?) composite. Each should be able to hold a ~500 sq. ft. sail (square-top & fully battened). Most likely I'll go with wishbone booms. I would plan to run a large mizzen staysail (~600sq.ft.), with running backstays if necessary.

    Can composite masts be built large enough and strong enough[/QUOTE]

    G'day,

    A very smart choice.

    An unstayed mast is an easy object to engineer as the loads are so well defined, compared to a stayed mast, hull or rudder. Our engineer charges $AUS1,000 for the task, including the beefing up of the hull, which is a very easy task.

    They are easy to build in a simple, cheap, easily built mould (mdf and formica). I sell plans including instructions for building them and fitting them out for another $Aus1,000. You will need a vacuum pump, but these are cheap or can be hired.

    I don't know what the righting moment on your boat is, but size is not a problem. In fact, the bigger the mast, the easier it is to work on the laminate. The boat on http://www.youtube.com/watch?v=8chR6DAFjGA has far higher righting moment than yours and similar sail area, and the mast works very well, and is about the same weight as the bare alloy tube on an equivalent stayed rig.

    Unstayed masts can be built with carbon tow which is half the price of carbon uni. Both are cheaper per unit of stiffness (which is the critical criteria for mast design) than timber. At a small increase in weight and a large decrease in cost, it is possible to use glass for the off axis material.

    Uni carbon costs about $100 per kg, tow $50. Off axis carbon about $200 (which is why we use glass at $6). Two thirds of the laminate will be uni or tow running along the mast.

    There will be about 1 kg of resin ($20) per kg of reinforcement. So, 2 kgs of tow ($100), one kg of off axis glass ($6) and 3 kgs of epoxy ($60) is $166 for 6 kgs or $28 per kg. This will probably be cheaper than a bought alloy mast, never mind all the rigging.

    A pro built mast from us is about the same price as a rigged alloy mast in Australia, as per the thread on http://www.cruisersforum.com/forums/f116/unstayed-masts-stayed-masts-12995.html

    The pro built masts will have a bit less resin per kg of reinforcement than an amatuer built one and are built in one piece. The amateur built one will be a bit heavier, but just as stiff and strong.

    The problem with pro built masts is that shipping is ridiculously expensive. For this reason, we are working on telescoping masts, which will not only reduce weight and windage aloft when reefed, but will be very cheap to ship in a container.

    Wishbone booms are great, although a little trickier to build. We use booms fixed solidly to the masts which are easier to build and less hassle to operate.

    Please let me know if you have any questions.

    regards,

    Rob
    www.harryproa.com
     

  8. Seafarer24
    Joined: May 2005
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    Seafarer24 Sunset Chaser

    It was definately a Cheoy Lee 43 MS, but they had completely cut away the cabin-top along with the side and after decks, and part of the after top-sides. The only part of the boat not "affected" by the fire was the forward stateroom, which had a lot of smoke damage. The hull itself appeared entirely sound, but the project was FAR more than I'm willing to take on.

    If they had at least gutted it, I might have been tempted.

    As it is, I've checked out an Offshore 33 and Herreshoff 31 that are both in the same price range. The interiors are decidedly un-inventive but functional. Either one would be fine, and both have their positives and negatives.

    The Offshore has a nice wide cockpit, with integrated LPG tank holders and many huge cockpit lockers. Also, the side cockpit lockers have removeable panels that let you access the sides of the engine. This particular Offshore had standard booms and fully-battened sails!

    The Herreshoff was an '85, which meant it was one of the fiberglass hulls built in Miami. However, the interior was still all hand-built from Honduran pine. This made it very beautiful, and also much easier to modifiy than the Offshore (which uses a fiberglass liner). Also, I prefer the rounded bow profile this boat uses over the raked bown of the Offshore. The entire boat has a more classic/classy look to it. The transom-hung rudder has steps built into it to aid in coming aboard if you fall off- pretty damned cool feature for a factory-built boat. This particular Herreshoff had the optional 3' shoal draft. I would probably prefer the 4' draft and better windward ability, but it's not a deal-breaker.

    Rob- thanks for the information, if I decide to build a boat of my own I will seriously consider going with your company for the masts.
     
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