Flexible non-steamed wood for gunnels?

Discussion in 'Materials' started by sprit, Oct 19, 2013.

  1. sprit
    Joined: Jul 2013
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    sprit Junior Member

    I would welcome information about the most flexible non-steamed wood that is commonly available and suitable for making permanent gunnels.

    The wood must bend both around the side of a bow (minimum radius is 21 feet) and up to a bow. A square cross section is therefore needed.

    Is low specific gravity a good guide?

    I plan to protect the wood with 6 oz glass in epoxy, and to paint, so the wood will be well encapsulated.

    I do not want to cut partway through one side of wood strips in order to make them more flexible.

    I do not want to use plastic or canvas-coated rubber instead.

    Of course I know that I can laminate strips.
     
  2. upchurchmr
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    upchurchmr Senior Member

    How big are you planning on?
    The Yost SOF kayaks bend 3/4 x 1 1/2 cedar thru a 13' arc with 1' of bow. Don't know how big that is in radius.
    But there is minimal if any vertical bend in those boats. I would guess it would be reasonable to put 2-3" of vertical bend at the same time, but I haven't tried it.
     
  3. SamSam
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    SamSam Senior Member

    It's a vague question so you'll get vague answers.

    What kind of boat? Do they have to supply strength also? Do you have any idea what size they are going to be? Will they be subjected to wear and tear? Is it a work boat or a pleasure boat? Can you supply a photo?
     
  4. michael pierzga
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    michael pierzga Senior Member

    Mahogany is a reasonably flexible straight grained wood. I like to use it for gunnels , toe rails and combings.

    Teak is another good choice if you can find it.

    Clear Pine is also a good choice...pine makes nice lofting battens .

    Cypress would be another wood to consider.

    If you are going to force the wood into shape be sure that the sticks of timber you choose have parallel grain...no grain run out.

    Grain Runout will split as the boat ages.

    You could laminate , but its tedious .
     
  5. El_Guero

    El_Guero Previous Member

    ... Why?
     
  6. peter radclyffe
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    peter radclyffe Senior Member

    american or canadian rock elm
     
  7. PAR
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    PAR Yacht Designer/Builder

    If these are just decorative pieces, then look at one of the several light softwoods. Most bulwarks or raised gunnels are required to hold things, which may be simply the stanchion bases, though they also may need to carry sheet tracks, snatch blocks, resist dock and mooring line strains, etc. This is why most are hardwood.

    If having trouble bending a solid piece of desired size into position, consider laminating small stock, which is usually more compilable to bending wishes.

    [​IMG]

    This is one of my designs with a raised bulwark. It stands clear of the deck so it'll shed water on the deck and the upper section is made up of 1x2's, glued and stacked in place. The whole shebang, when cured is through bolted to the sheer clamp. It can carry sheet tracks, snatch blocks and most any loads you want to impose on it. The Douglas fir 1x2's are easy to bend in place on their "flats", though someone helping twist them in place, as you apply clamps or temporary fasteners, until the goo cures is a good idea.

    I've made this style of bulwark for years and it's not hard, though a little tedious, compared to a single piece that's bent in place. I do usually scarf the individual layers within the laminate, but this isn't entirely necessary. A decorative version of this wouldn't need to be 1.5" thick, so maybe just .75" square stock, glued into a suitable height stack will work for you.
     
  8. sprit
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    sprit Junior Member

    The boat in question is a 5 x 18-foot power skiff with a springy sheer line and a nicely rounded bow. The gunnel wood would be OK at 1 x 1" square. But 1.5 x 1.5" would be better. I have previously tried 1 x 1" mahogany and found it too stiff. I was able to laminate 1 x 1/2" to a previous boat, but thought there was probably a more flexible wood for my next boat. The gunnels do help stiffen the top edge of the 1/2" marine plywood sides. Nothing will be attached to the gunnels. As noted, the gunnel wood will be protected by glass, epoxy and paint.
     
  9. alan white
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    alan white Senior Member

    Three laminations of 1/2" wood would make your 1 1/2" thickness. Ash is readily available and pretty hard, yet it bends beautifully especially when steamed (steam and clamp and when dry glue up in place).
    Depending on the rise of the sheer towards the bow, the wood may or may not bend upwards easily. If the piece has to take much edge set, you could cut curved sections wider than 1 1/2" and then assemble and sand in place after gluing, especially with an eye towards using existing curves in the grain.
    White oak would be tough and would bend/steam well, but while you could use epoxy to glue it, you should prepare the wood by wiping with acetone first before gluing (others may give better more complete advice on that preperation). White oak won't adhere as well as other woods using epoxy, though it isn't a real critical application.
    Oak while amazingly tough will check more than a soft wood. You would need to keep it well protected (maintained) to prevent checking.
    African mahogany is another very attractive choice. Little problem with checking or gluing, cheap enough to buy and hard enough to hold up.
     
  10. PAR
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    PAR Yacht Designer/Builder

    Recent tests at West Systme show 97% of peel strength (white oak) as other similar, less difficult to bond hard woods if prepped properly.

    Mahogany is notoriously difficult to bend, even if steamed. Dry bends will usually result in 50% or better breakage. This said, if you work with thinner stock, you could decrease the breakage by a bit.

    Bending wood doesn't necessarily mean a steam box. Boiling water poured over towels, that are draped over the stock works, as does a heat gun. One of my favorites is a tile cleaning steamer. I just hold it against the plank and wait. 3/4" stock steams quickly, though mahogany is still a prick to bend.
     
  11. El_Guero

    El_Guero Previous Member

    Thank you.
     
  12. Steve W
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    Steve W Senior Member

    Im curious as to why you dont want to steam, its very easy to set up, cheap , lots cleaner than laminating and this is a perfect application .

    Steve.
     
  13. Petros
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    Petros Senior Member

    clear grained western red cedar would likely take a bend like that at about 1.5" square, choose some wide grain low density material.

    The problem is that it does not have a lot of cross gain compression strength, so it is easy to dent when using it as a rub rail (the grain is easy to crush).

    Straight grain western hemlock is reasonably flexible and yet fairly strong, but it has almost no rot resistance. If you can get it and treat with preservative it will resit rotting.

    I would use alaska yellow cedar, a very different type of cedar wood, straight tight grain, dense and excellent cross gain compression strength (used often for deck planking), and rot resistant. But you would likely have to heat them to get them to bend nicely, it responds very nicely to steam bending (unlike a lot of other wood). You do not have to steam it, get a long trough or tray of water hot and put the end in it that you need to bend for about 20-30 min, and than clamp it up and force into your bend. it will not split or crush.
     
  14. PAR
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    PAR Yacht Designer/Builder

    I would go with white or live oak (preferable live) for this piece, knowing the job it'll have to do. Both bend well with heat or steam. If you wanted the softwood route, Alaskan cedar is good, if soft, but I would look at Spanish cedar too.
     

  15. sprit
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    sprit Junior Member

    I have been reticent about steaming because of inexperience, lack of equipment, because the pieces are long, and because the curves are arcs, i.e. steaming at one end won't work. I had hoped that a wood with lowish density and respectable rot-resistance (perhaps northern white cedar) might work without steaming. And I assumed that protecting the wood with 12 oz biaxial glass in epoxy would compensate for the softer wood. But many of you have encouraged hot water as a way of getting easier bending of stronger pieces with good cross sections. I'll try it, and thank you all.
     
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