cedar and fir composite mast

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

  1. Submarine Tom

    Submarine Tom Previous Member


    Now you're talking.

    Of course, "If God had meant for boats to be made out of fiber glas, he/she would have made fg trees."

    Collin, don't get me wrong, I use fg all the time.
     
  2. PAR
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    PAR Yacht Designer/Builder

    Wind surfer masts are generally way to bendy to use in a boat. And they do break, often easily, if used in a boat, typically from point loading by installing it over a stub.
     
  3. Collin
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    Collin Senior Member

    I think it's worth a shot because:

    1. windsurfing masts have been adapted before with success. (see Gary Dierking's boats)

    2. a timber mast presents a good amount of construction time, especially if hollow....It's already June!!!
     
  4. Collin
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    Collin Senior Member

    :D thanks
     
  5. PAR
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    Collin, Gary Dierking's use of windsurfer rigs places them in a similar environment, which is to say they they're free to flex at will and not restrained, except by a sheet. Try anything else with a windsurfer rig and you'll quickly find out what I mean. I've done it, also thinking it would be an easy way to get a rig, but multiple failures makes for a simple alternative solution, more viable. I'm not the only one that's made this discovery.
     
  6. kerosene
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    kerosene Senior Member

    would a tree be too heavy? As in a whole top trunk of a small fir?

    That is how we do flag poles and I was planning on using one on my dinghy.

    Seems light enough. I hung it vertical in a tall barn to dry so it would stay straight.
     
  7. Collin
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    Collin Senior Member

    No, a tree will work just fine and save you a lot of building time.
     
  8. Collin
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    Collin Senior Member

    What happened to the masts? Did they break?
     
  9. PAR
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    PAR Yacht Designer/Builder

    Yep, they break, pretty easy too. Unless they're free to flex all they want, they snap like twigs. They're just not designed to be "restricted" in movement. On a windsurfer the heel is captured, but the rest of the stick if free to do what it wants.

    A tree is a lousy mast folks. On a big yacht, where you can afford the weight penalty, not as big a deal, but on small craft a real sailing ability killer.

    Collin, what boat is this mast going on? Make, model, year, etc.? Lowe's/Depot sell a stud called "white wood" which typically is white pine or some sort of spruce. Because it's crap stud stock, it's full of knots and defects, but you can get it cheap and because it's a fairly light wood, good for mast stock. You do have to eat a lot of these studs to produce enough for a mast (50% waste wouldn't be unreasonable), but considering what good mast stock (Sitka) costs, worth the bother.

    A box section mast, is about as easy a thing to make as you could ask, at a fraction of the weight of a solid tree. Birdsmouth is a light weight method for a round mast, which looks much better to most eyes.
     
  10. Collin
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    Collin Senior Member

    The mast is going on a shortened (15') skin on frame version of Dierking's Ulua design. I'm going to try spreading 60 square feet, which happens to be about the most the boat can handle. I originally made it for paddling, but I built it with a mast step and discovered how much fun sailing an outrigger canoe is and the hull is only 30 pounds.

    I have enough fir to build a box mast, but I'd need to cut scarfs, calculate stave thicknesses, glue it together, finish it. The end result would be good, but I'd rather just pick up a ready built mast and sail and get on the water.
     
  11. PAR
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    PAR Yacht Designer/Builder

    On a boat like that, you'll want as light a mast and rig as you can possible install. A ready built mast is an aluminum tube (T-6) of appropriate dimensions and wall thickness.
     
  12. Collin
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    Collin Senior Member

    Where do you find that sort of thing?

    I just want to say for people new to boat building, I've made a few box masts and I've been really happy with them. You always hear of either solid or birdsmouth, but a box mast gives you the best of both worlds in terms of lightness and ease of building.
     

  13. PAR
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    PAR Yacht Designer/Builder

    Aluminum comes in several alloys. Accept only 6061 (T-6) aluminum for masts, especially if free standing. It has to be sized properly so it doesn't buckle under load too.

    Most can get a local welding shop to order 6061 aluminum tubing. Don't be confused with aluminum pipe, which is generally not as strong. Also tubing is usually listed as OD, but pipe ID, so a 2" pipe will permit a 2" ball to roll inside it's length, but not in a tube.

    A 1.5" tube with a .058" wall will likely be sufficient for 60 sq. ft. and will weight about 3.75 pounds. Of course I've made a number of assumptions, so the mast scantlings should be "scaled" appropriately for it's role.
     
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