Rotating wing mast

Discussion in 'Multihulls' started by john olsson, Jun 8, 2007.

  1. john olsson
    Joined: Oct 2005
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    Location: Sweden

    john olsson New Member

    By reading posts in the forum I decided to design and build my own rotating wing mast. My idea is to strip plank a half wood wing section, glass inside and outside and then join the two, put a sail track on the trailing side. The wing section I believe can be design simply by using the specifications given on the building plans for the catamaran eg. Inertia(1)*E modulus(aluminium mast)<= (less or equal) Inertia(2)*E modulus(wood).
    Is there any more I should consider?....
    Reading Rob Denney. and Eric Sponberg maybe I should go the carbon way instead? Eric suggestion is to design all the load in the carbon, and Rob showed a carbon strip planking technique.

  2. frosh
    Joined: Jan 2005
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    Location: AUSTRALIA

    frosh Senior Member

    You are not doing a compound curved shape with a wing mast. Why use stripper methods then? Also skin stiffness is not the main issue, but stiffness of the entire mast section. For this and ultimate strength, nothing will better prepreg carbon as a single skin, and vacuum or pressure mold and an autoclave. Most home builders will compromise in one or more aspects of this ideal. However your suggestion as as nearly as far as the polar opposite of the ideal. Why?? Surely even very thin marine plywood held in half section aerofoil shape, and carbon/epoxy layers hand layed up, on each side; and finally the two half sections joined would be much better than strip planking up a mast. A carbon mast track is easily incorporated into the trailing edge of the two halves at the time of joining up. Remember we are in an age of materials science hugely further advanced than the beginning of the 20th century.
  3. john olsson
    Joined: Oct 2005
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    john olsson New Member

    technicaly simple production

    As a homebuilder, strip planking is easy ant a straigt forvard method of construction. Wood is by all means very good for structural use, compared to others, but carbon fibre(CF), could be lighter at increased expenses. The design criteria that my mast has to achive is .
    Lighter than alu standard mast,(5,1 kg/m*12,5m=60kg).
    Stiffer, bigger section would also make it more stiffer.
    Cheaper, building myself.
    With these design criterias, wingmast 12.5 m 60 kg or less cheapest possible.
    Stripplank is good enough.

  4. catsketcher
    Joined: Mar 2006
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    Location: Australia

    catsketcher Senior Member

    It may be heavy

    Hello John

    I made a strip wooden wing mast for a 38ft tri once whilst I had to make a mast for my 38ft cat. The wing had lots of carbon and was made from 20x8mm cedar. It was nice enough to make but was heavier than the alloy mast by a fair bit. For us cost savings after we -
    -made a mast bench
    -made MDF stations
    -bought cedar strips
    -scarfed and glued cedar strips
    -bought reinforcing timber or glass for tangs etc
    -got custom mast hardware made
    -paid for lots of bolts to bolt track to mast along with track
    -paid for vacuum materials for vacuum bagging
    and more made the wing mast much more expensive than an aluminum one. The mast ended up heavier than it should and we bagged the whole thing.

    My advice with masts is not to make a rotating one but get a nice solid alloy kit one and spend more time and money making the boat a little longer. More payload, better ride, better resale and no problems with insurance. Rob Denney would disagree with me but it took me two days to make a 46ft alloy mast from a kit and almost two months to make the 46ft wooden one. You gotta fair it and paint it too. Lots of weight and time. In my experiment the alloy kit mast won hands down.

    Good luck for your project


    Phil Thompson

  5. waikikin
    Joined: Jan 2006
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    Location: Australia

    waikikin Senior Member

    John, Ive got a busted strip cedar carbon mast laying in my yard, it bears out what catsketcher is saying in that(I hav'nt weighed it) it feels pretty heavy & having salvaged it for a couple of fittings & the rcb track, it dont look worth repair even though this should be fairly strait forward.Retro Fitting stuff to this kind of stick isnt as easy as drilling & tapping a couple of holes either. Of course their may be a $ saving angle on the strip job & it might be fun to make too. Allthe best from Jeff:)
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