balsa core, endgrain or not?

Discussion in 'Materials' started by sigurd, Feb 6, 2009.

  1. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    When considering a cheap canoe hull, I am thinking of using balsa core, with longitudal hardwood and glass sheath. With the cost of all the epoxy I think pure glass will be as expensive as the hardwood veneer, for the same puncture and abrasion resistance? With the veneer I'd put 50gsm glass between it and the core, on the outside. The inside could be veneer, but light glass, 200gsm or so would probably be cheaper.

    You can get endgrain balsa or planks. If I use planks, I'd lay them in the transverse direction. If I get endgrain panels, I'd have to consider strengthening the skin in the transverse direction.

    But which one will be more impact resistant?
     
  2. TeddyDiver
    Joined: Dec 2007
    Posts: 2,587
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Endgrain..
    Just curiosity, but how thick panels you are talking about??

    MVH Teddy
     
  3. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    balsa: if planks, 4mm, endgrain is 6mm.
     
  4. TeddyDiver
    Joined: Dec 2007
    Posts: 2,587
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Have you a mold ?? You need one for endgrain sandwich. Otherwise it's easier to make stripplanked and then you get better results with spruce..
     
  5. waikikin
    Joined: Jan 2006
    Posts: 2,379
    Likes: 149, Points: 73, Legacy Rep: 871
    Location: Australia

    waikikin Senior Member

    Have a look for Michael Storer or Known here as boatmik , he did a nice longtitudinal balsa planked canoe. Regards from Jeff.
     
  6. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    Waikikin, I saw one on the net - could be the same canoe.
    Less than 6kg it was, 7mm core with 75 alternating 150 gsm glass.
    Teddy, I have been considering stripping birch, spruce or similar, as well. I think I would need a total of 3mm laminate, then. It would be much less stiff, but puncture and shock resistance should be easier to get, I think? I've never seen endgrain balsa. I'd build a mold from stringers on a frame - I assume you don't think it is necessary with a complete mold?
     
  7. robherc
    Joined: Dec 2008
    Posts: 432
    Likes: 5, Points: 0, Legacy Rep: 102
    Location: US/TX

    robherc Designer/Hobbyist

    sigurd:

    For abrasion resistance, glass is OUT...try Kevlar, or better yet (if you're prepared to do some vac-bagging) Dynel for the outermost layer(s) if you're wanting a surface that'll stand up to a good bit of bumping & grinding + dragging & scraping. The Kevlar adds strength similarly to e-glass, but is pretty expensive; the Dynel doesn't add much strength, but is the BEST for abrasion resistance.

    As far as the balsa, end-grain is a good bit stiffer & more impact resistant, but it's also harder to work with in tight curves. You'd almost be better off cutting the endgrain into strips & strip-planking with it than anything else, IMO.

    Just my $0.02(US, unfortunately), take it for what it is/isn't worth ;)
     
  8. PAR
    Joined: Nov 2003
    Posts: 19,133
    Likes: 482, Points: 93, Legacy Rep: 3967
    Location: Eustis, FL

    PAR Yacht Designer/Builder

    Dynel or for that matter Xynole (which is 2 times better then Dynel at abrasion resistance) will suck up huge amounts of resin and make for a heavy laminate. Kevlar is the fabric of choice if the ultimate in both regards is required.

    I don't think a cored structure is the cheapest way to build a light canoe. Even if the core is inexpensive, the goo and fabric cost will be higher then other material choices.

    Impact resistance is a pretty relative term in regard to a small, light weight canoe. A good light weight species plywood and a thin sheath is fairly hard to beat, pound for pound, dollar for dollar.
     
  9. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    PAR, I agree with your assessment of thin plywood, but to get the shapes I want, it would have to be cut up a lot I think. So in that case it might make more sense to me to laminate the plywood myself. But the stiffness of the balsa laminate is alluring, so i'm trying to find a cheap way to make it abrasion and impact resistant. To that end I was thinking of using ipe or another hard, strong wood as the outer 0.6mm sheath, 50gsm glass under it, and a thin glass sheath on the inside of the hull, the glass sheaths could be reinforced with carbon tow (also cost effective for me now, in small amounts). Not sure what to expect from such a laminate though, and using a much thinner and denser core like spruce or birch at least in the bottom seems the safer way but needs more supports.

    Kevlar vs hardwood as sheathing, it would be interesting to know the differences.
     
  10. TeddyDiver
    Joined: Dec 2007
    Posts: 2,587
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    Birch is too heavy and has other issues too.. Stringer mold (for endgrain) is allmost a ready strip planked body so it's excess work.. but possible. In thin cores endgrain balsa sucks relatively lot of resin and there's hardly none if any weight benefit compared to stripplanked spruce.
     
  11. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    How much resin?
     
  12. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    http://www.powerandsailmarinesurveyors.com/Serv 05 end_grain_balsa_core.htm
    That is a lot of epoxy. How much does spruce need then?
     
  13. TeddyDiver
    Joined: Dec 2007
    Posts: 2,587
    Likes: 125, Points: 73, Legacy Rep: 1650
    Location: Finland/Norway

    TeddyDiver Gollywobbler

    To make a quess maybe 1/4 compared to endgrain balsa but it greatly depends of the quality, density and humidity% of the timber (balsa and spruce or any timber) and the viscosity and ambient temperature among other things so only a test will tell.
     
  14. robherc
    Joined: Dec 2008
    Posts: 432
    Likes: 5, Points: 0, Legacy Rep: 102
    Location: US/TX

    robherc Designer/Hobbyist

    Kevlar:
    Strengthening is encapsulated in resin, and is a waterproof fiber...so as long as the Kevlar is still at all in-tact, there is no danger of rot.

    Hardwood:
    Covered in Epoxy for waterproofing, and (depending on the wood) can be water & rot resistant, though not to the degree of Kevlar. Thicker than Kevlar fabric laminate, so can last through more long-term abuse before "wearing through" and needing replaced (probably easier replacing the whole boat).

    This is by no means an exhaustive comparison, but I think it'll give you an idea of the balance here. Waterproof/rotproof vs. Longer-life, lower-cost. ;)

    (You can, however, extend the life of the Kevlar with very little weight added by using 2-3 layers of Kevlar...drawback: higher cost)
     

  15. sigurd
    Joined: Jun 2004
    Posts: 827
    Likes: 8, Points: 18, Legacy Rep: 65
    Location: norway

    sigurd Pompuous Pangolin

    Wonder if norway spruce is a good strip material?
     
Loading...
Forum posts represent the experience, opinion, and view of individual users. Boat Design Net does not necessarily endorse nor share the view of each individual post.
When making potentially dangerous or financial decisions, always employ and consult appropriate professionals. Your circumstances or experience may be different.