Tree species for a big mast

Discussion in 'Sailboats' started by ShaneK, Mar 19, 2014.

  1. Mr Efficiency
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    Mr Efficiency Senior Member

    When James Cook discovered Norfolk Island in the South Pacific in the 1770's, he was struck by the impressive stands of tall Norfolk Pines, and immediately saw potential in them as masts for the fleet, alas they proved quite inadequate for the task.
     
  2. rwatson
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    rwatson Senior Member


    hahaha - love this

    Whats the term when a mispelling also hints at related actions ? :)
     
  3. Mr Efficiency
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    Mr Efficiency Senior Member

    I can't see a spelling error, though ? I say you have given a wooden explanation I saw right through. :D
     
  4. rwatson
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    rwatson Senior Member

    yeah, sorry - I explained that badly. I should have said one word that had two meanings, but both applied to the subject.

    Dont mind me - it was just a brain snap :D
     
  5. BobBill
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    BobBill Senior Member

    I get to some of this material late, but a mast that large is quite the undertaking and as noted best hollow, but unstayed seems a bit far, at least to me.

    Would like to be kept in the loop. Fascinating undertaking.
     
  6. ShaneK
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    ShaneK Junior Member

    BIG timber mast

    LoL@gggGuest.
    Thanks for all the feedback. I am well aware of the enormity of the undertaking.
    The reason for unstayed are two-fold.
    1) I want either a wingsail, or junk rig. Is small scale experiments with a unique wingsail work, then that is what I will build.
    2) I could use stays to masthead, but that adds another set of calculations, reinforcing and risk in coping with the tension of the stays in the hull.
    I have probably 12ft between keel and deck, and the 100ft stated is for the whole mast.
    I was thinking Douglas fir, which I believe is grown in Scotland, and grows to 200 - 300ft. Whether the Scottish stuff is nkot-free-enough is another matter. Slow grown timber is generally better ... maybe Scandinavian will be required. It would be constructed, hollow, prob' 10-15% wall thickness, and reinforced with composite (unidirectional). The figures I found indicate that glass/epoxy has 3x elastic stiffness, and 10x fail load ... in tension. I have only built aeroplane wings and centre spars in uni' before, where the compression member was 1.3, maybe 1.5 times the thickness of the tension one. Obviously, compression is an all round aspect of a mast.
    Ultimately, the load on the mast is only as much as the stability of the ship can return. Equal and opposite reaction and all that. I have no idea at this time what the righting moment will be after I have added internal ballast, and almost certainly added to the keel ... another serious job.

    Overall, I do have a habit of making crazy ideas work !

    Regards
    Shane
     
  7. BobBill
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    BobBill Senior Member

    Shane, I understand your penchant for adventure. I too do similar madness in a different place...so we do together in different places together.

    Now, considering the strategic view (long term) why not go with alum or carbon or a combo?

    Wingsails are only practical (to me) when they can be dropped...and there are a few designs that do that and are shown on the WWW.

    I am piddling around building an outrigger based on the Malibu Outrigger orig design and plans, using recycled Hobie 18 and 16 hulls (long story) and the plan calls for 26 foot Sitka spar...no way, so I am using combo of recycled and sleeved surfer masts and T6 AL tube at low end...crafting involved, and though smaller scale, similar to your goal...from a pragmatic view, gggguest, Par and Eric are tops, not to detract from others willing to help, so touch hands with them and take their advice to heart.

    Fun, eh...youzer.

    You must keep us posted.
     
  8. ShaneK
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    ShaneK Junior Member

    @rwatson A friend would call it a brain fart !
    I like word play too.
    I believe that the American revolution was caused as much by the English claim to ownership of all the mast-making Eastern White Pine as by the tax on tea.
    I am also an innovative engineer, though I do lack the maths, I make up for it with a general understanding of physics, and lateral thinking. Thinking outside the box .... what box ? LOL
    Ally/carbon ... basically cost, plus my boat is timber with a composite sandwich superstructure. Far too much modern materials as it is. If the concept works, I am likely to completely remove the superstructure again ... or see if I can find another one of these boats.
    My wingsail concept is variable camber for P/S tack, and fabric, so it can be reefed/lowered.
     
  9. BobBill
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    BobBill Senior Member

    Will get you thinkin' and am sure other sites lurk about also.

    I was thinking of crafting a soft wing to emulated old bi-plane winds which were simple, fabric and wood "sticks," in some cases. But gave idea up to expediency using cast off Hobie 16 main...to get the rig going this years.

    Simple is best...usually in the beginning and almost always later.

    http://forums.sailinganarchy.com/index.php?showtopic=153121
     
  10. Nick.K
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    Nick.K Senior Member

    Hello Shane
    Where are you in Ireland? I have just made a solid tree mast (11m) out of native Douglass and I am currently finishing a laminated mast (10m) out of imported Douglass. I have made and repaired quite a few timber masts, the imported Douglass is a great timber and a built-up mast allows you to select the best pieces while tree masts have inherent weaknesses, especially the tendency of knots or splits to wick water in to the centre which can rot.
    A long mast is no problem, just scarf the lengths together then prepare the halfs with the appropriate taper before gluing them up. Stagger the tapers.
    Aerodux is a good alternative to epoxy, the pot life is longer and it is more moisture and temperature tolerant although the dark glue lines can be unattractive on long scarfs.
    Nick

    Edit.
    I used Prefere 4094 not Aerodux on this mast
     
  11. ShaneK
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    ShaneK Junior Member

    I am in Ireland Balbriggan). I consider the prospect of steaming up to Scotland to collect the segmented Douglas firs. I anticipate making a cutting table, probably using a full length RSJ (welded lengths), to cut tapers, birdsmouth, channels for grp, and support the whole thing for glueing and finishing.
    I have asked Wessex Resins for their recommendations on epoxy. They can formulate a flexible epoxy to match the elasticity of the wood to reduce shear stresses between glue and wood.
     
  12. Nick.K
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    Nick.K Senior Member

    A straight table is a help but not absolutely necessary. Trestles work as well and being wide you can roll the mast over. The most useful tool is a string line which can be used to mark out long tapers or to find the centreline of curved pieces of timber.
    Is the Scottish timber knot free?
    Nick
     
  13. SukiSolo
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    SukiSolo Senior Member

    I would advise cutting out any knots in native UK Douglas Fir. I am using some stuff grown locally (South UK), a 100 foot tree, of which I had the lower part planked. Great stuff but a little wide grain spacing. The knots are incredible weak points but if you are careful and scarf clean timber together it is a great material.

    I'd also second that there are adhesives other than epoxy which can do the job. Cheaper and sometimes easier to clean up, all into the bargain.
     

  14. ShaneK
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    ShaneK Junior Member

    Trees for masts

    Knots, or their absence is largely to do with care while growing. Colder climate = slower growth = finer grain.
    Straight bench will be welded RSJs, then attach cross members shimmed for straightness.
     
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