cedar and fir composite mast

Discussion in 'Boat Design' started by Collin, May 22, 2012.

  1. Collin
    Joined: Nov 2011
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    Collin Senior Member

    I have some air dried red cedar and fir that would be perfect for a mast. Of course, you hear that cedar is too brittle for a mast. But I was wondering, if I put the fir on the outer 2 sides (this is a hollow box beam) we could get away with using the cedar on the portion of the mast that has less stress.

    Or would I just end up with a snapped mast?
     
  2. gonzo
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    gonzo Senior Member

    Just about any wood can be used for a mast. Red cedar will need bigger dimensions than fir. I had a 40' sprit of cedar that gave me good service and never broke.
     
  3. PAR
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    PAR Yacht Designer/Builder

    The two dramatically dissimilar material densities will undoubtedly cause issues, even well stayed. Fir is going to be 50% more dense than cedar. I'd elect to have the fore and aft planes use the denser stock, though it wouldn't be something I'd willingly do, letting the shrouds carry the side loads as best as they could. Red cedar isn't my first choice to hold fasteners either.
     
  4. Petros
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    Petros Senior Member

    I have done similar things by mixing both cedar (low density) and doug fir (high strength) with good results. The loading on a stayed mast is a complex condition, likely highest loading occurs where the boom attaches. A cantilevered mast has highest stress at the deck of course.

    You might just use the doug fir, and make it hollow. both dough fir and wrc had similar strength to weight ratios. So you can get the same overall weight of mast with either material, you just use thinner sections out of DF. Put a solid block at the point where the stays and boom attache to it (drill a hole the length of the block so it will not trap water inside).

    Cedar has low cross grain compression strength, and lower fastener hold power than doug fir.

    Good luck
     
  5. Submarine Tom

    Submarine Tom Previous Member

    Yellow cedar, fantastic.
    Red cedar... Not so much.
    Fir, terrific!
     
  6. Collin
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    Collin Senior Member

    Hmmm this is not looking like a great idea.

    I got the idea from Gary Dierking making crossbeams from solid wood and widewalls of plywood

    [​IMG]

    If someone can make crossbeams out of the worst material possible, why not a mast :D
     
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  7. Submarine Tom

    Submarine Tom Previous Member

    Hey, don't let me hold you back.
     
  8. Collin
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    Collin Senior Member

    But one snapped mast is too many :D
     
  9. PAR
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    PAR Yacht Designer/Builder

    Masts need to be light, strong, stiff and accept fasteners well. Plywood will have 1/2 it's veneers running the wrong way, so you're just carrying them along for laughs (and lots of extra weight). There's no place on a mast where plywood is acceptable. Cross beams are a wholly different beasts than a mast. A mast is a column and this is treated quite differently then a beam.
     
  10. Collin
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    Collin Senior Member

    That makes sense.
     
  11. Collin
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    Collin Senior Member

    I've been trying to find some more wood to make the mast and the wood quality around here as gone way down hill. My reliable source of clear studs for $1.69 seems all dried up.
     
  12. PAR
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    PAR Yacht Designer/Builder

    Most places don't know good wood from bad. You can go through a stack of flat sawn stock and find quarter sawn and they'll charge the same thing. You can also select flat sawn stock, rip it down the middle and get quarter sawn, depending on where in the tree the piece came from, so you are the best guide for getting stock, not the supplier. With same quantities, you should be able to pick out each stick, checking end grain orientation, defects, etc. Every Tuesday morning, the local Lowe's folks know I'll be going through their newest shipment, just for this reason. In a stack of 150 sixteen foot 2x12's I'll find about a dozen dead perfect, straight grained, knot free pieces and it doesn't make sense to let this stock go into someone condo roof.
     
  13. mydauphin
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    mydauphin Senior Member

    Find a lumberyard that can buy what you want straight from the Mill. They can get you whatever you want, and they will cut it for you. The only issue is cost, but you only have to do it once.
     
  14. Petros
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    Petros Senior Member

    Aah! So that is where all the good lumber from the stack has been going. Obviously I need to get there before you!

    Seriously however, the wood in the costly specialty boat store comes from the same place as Lowe's and Home Depo get it, from a tree. the difference is one is hand selected from the stack. No reason you can not do that yourself. I regularly find excellent wood at the big box stores, but it is rather random, and you have to stop by regularly and take your time accumulating the good lumber for your project well before you intend to start building.

    I have also bought fair large size lumber, and than remilled it into stringers. All clear straight grained stringers go into one pile, the other pile gets used as spacers, temp bracing or firewood. The wood is so inexpensive from the big box store you will save a lot of money even if 2/3 of it is never used.
     

  15. Collin
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    Collin Senior Member

    I love skimming the good wood out of Home Depot and Lowes. But lately I can look through their entire selection and come up with maybe a couple decent boards after having picked through 100+ boards with terrible knots and terrible grain.

    I think I've found the solution for small boat masts....windsurfing masts! I know I'm taking another idea from Mr. Dierking. They're cheap, plentiful and unbreakable.
     
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