Outrigger canoe plan....

Discussion in 'Multihulls' started by BWD, Aug 2, 2006.

  1. BWD
    Joined: Aug 2006
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    BWD Senior Member

    Hi. I am a novice to boat building although I have built some kiteboards and various non-nautical objects, mostly wood and wood-epoxy composite.
    I have a plan to make a18 ft sailing outrigger canoe. As I am a windsurfer also, I want some speed from it. I have been thinking of using the cylinder molding technique to build the vaka, and want a flattish run aft. I have attached lines below, and would be grateful for any experienced cylinder molders who could advise if this shape is likely to be workable with the technique, or if there is too much flattening (there's not that much, really...). I am planning 2-layer 3mm ply construction...
    Many thanks!
     

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  2. garydierking
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    garydierking Senior Member

    Outrigger canoe

    I think for a one off hull, you'd be better off strip planking it. Then you'd get exactly what you want.

    Gary

    http://gary.dierking.net
     
  3. BWD
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    BWD Senior Member

    Thanks. Given your experience, I may be better off following your advice...

    I would just order Ulua plans, but I am enjoying learning some CAD and have some sort of drive that compels me to try to go through the design process... Hopefully I will not come up with a dog, be it plywood or strip. I will try to post here once I get a hull built, and still welcome any cylinder molding advice. I have done some vac. bagging, and think CM is an interesting technique......
     
  4. frosh
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    frosh Senior Member

    I have recently built a 22ft. outrigger canoe in cold molded plywood using 2 layers of 1.5mm marine ply. Also it has a layer of 200 g.s.m. woven carbon over the outside and one layer of tightly woven 100 g.s.m. fibreglass over that. The centre section which is an open cockpit is also sheathed in one layer of similar fibreglass.
    Stiffness and strength of the hull is more than satisfactory. What makes a huge difference are structures that bridge across the gunwhales at regular intervals, even wood seats.
    Your drawings seem somewhere between an efficient planing hull and a slippery displacement hull. I am not saying that it won't work, only that it is not the ideal shape for paddling, nor for getting up on a plane.
    My canoe is for paddling and sailing under a dinghy spinnaker off the wind.
    The hull shape of mine is double canoe ended, semicircular in the centre, and a rounded V'eed section towards each end. The centre was molded from 2 sheets of 1.5mm marine ply 8 ft. x 4ft. in a single operation with epoxy glue between the two sheets. :)
     
  5. BWD
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    BWD Senior Member

    Thanks for the feedback. The shape is pretty elliptical through middle, should paddle and sail fast enough, track ok too (There will be appendages...). No plans to race. Entry is fine, but bow is not too pointy and there is rocker, it will have to handle light chop and gentle surf. Waterline L/B >10:1, planing not an issue. Fuller/flatter in the stern to support occupant who will be a bit aft of midship, esp. when occasionally 2 up. The back end is not pointy because it's not meant to be paddled through fast surf as much as sailed through slow surf; it should surf well in light Eastern USA swell of 1 to 4 feet. Our swell here is slower than what I saw in Hawaii, California. I imagine y'all have fast swell down under also. I would build a thinner tail for that I think.
    Planning on a sole just above DWL, the structure will basically be a box girder. Thwarts and akas will further stiffen it, ends will be decked. Tempted to go with lighter wood but don't want to pay for carbon or S2, so planning 2x 3mm okoume, biax tape over keel, 4 oz glass over ext. hull, sole. (Or may follow Dierking's advice and strip it afte all). May core the sole with balsa or SAN. Saving any carbon $$$ for the akas. Thanks.
     
  6. frosh
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    frosh Senior Member

    Hi, If you are planning to support crew weight on a sole then I think that you can reduce the ply to 2 mm. It will save weight which will improve the performance in the surf and speed generally. Also bending 3mm in such a narrow hull will be difficult. You can produce a much stiffer hull using thin ply by selecting the dominant grain direction in the plywood sections very carefully.
    If the ply is 3 mm you will have to select the dominant grain direction to run at right angles to the plane of bending, which is a weaker method of construction.
    On my boat two adults walk on the inner surface of the boats actual bottom skin with no problems. There is no need for a sole, saving weight. Buoyancy comes from each end which is sealed off by a bulkhead and decked. :)
     
  7. BWD
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    BWD Senior Member

    An update and a question:
    After much thought and fiddling with hull shape in CAD and some models I went with Dierking's advice and used WRC instead of tortured ply. Construction is 1/4 WRC strips sheathed in 9oz 8HS S-2, epoxy. Maybe overkill on the FG but I plan for hard use and "analysis" showed I would never break 50# without giving up a lot of strength, plus the glass was on sale.

    Built upside down over male molds, glassed outside and flipped to find there are spots on the garboard/keel strips! (unfortunately I made these of Douglas Fir of less than prime quality -thought it was good enough :mad: ) Spots are scattered, gray, and soft to poking with needle/razor. ROT! Pics below. And I built inside my heated home! The problem, I guess besides the poor strips, is that I had it sitting with the bottom glassed for over a week before I could flip it.

    Now the question. How to fix it? I have thought of:
    1. Carve out and replace the strips. It's just the keel, no big deal. :( Might be doable because there is 18oz of s-2 glass over the middle 6" of the bottom.

    2. Carve out and fill the rotty spots, pretend it did not happen.

    3. 2. plus some kind of anti-rot treatment before glassing inside.

    4. Cut him down the middle, replace keel, put it back together. Sounds absurd, but would at least make it easy to glass the inside of this narrow, deep canoe.

    Thanks to all who care to help an amateur!
     

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  8. nero
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    nero Senior Member

    Considering that it is a prototype with relatively little cost in material, perhaps the best path is to saturate the rotted areas and then glass it. The boat will last several years that way.

    Also, if you find that the hull doesn't perform as you imagine; you will have gained more time and experience for your next attempt.

    If the boat is to be stored out of the water, then there will never be enough moisture in the wood for the mold to continue to grow.

    Like the design. Maybe you could build 2 of the hulls and make a cool catamaran.
     
  9. tighkey
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    tighkey Junior Member

  10. BWD
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    BWD Senior Member

    Thanks, tighkey. I saw your thread -looks good.
    I would love to look at any files you care to send me, I usually
    work in delftship, have a trial version of rhino. FBM, DXF, PDF are my favorite file types.... I will PM you my email address.

    My vaka is a little fatter/longer and is being made to work with sail, motor, paddle, 2 adults or 3 children.
    Jack of all trades, master of none, I am sure.

    The little rotten spots have been carved out, treated and filled. Glassed in and out, inwales on. Working now on beam chocks, bulkheads and decks, someday it will be done...

    Some pics of progress below. Thanks again to all who gave advice.

    BTW the EG/Borate solution poisoned S3 epoxy so it won't cure. Had to dig it out of keel fillet and redo in a couple of areas where too much EG remained in keel joint. If doing rot tx again I would go for PEG and not much of it.

    Will post some more in later stages of build, rigging, launch. May take a while.
     

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  11. tighkey
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    tighkey Junior Member

    PLS find the attatched FBM for our V1

     

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  12. frosh
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    frosh Senior Member

    Hi, looking at your photo on the left of the woodstrips (Douglas Fir?), although I am not familiar with this timber it does appear slightly decomposed. If using premium resin and glue it makes sense to me to use premium timbers as well.
    In OZ Western Red Cedar is imported and costs a large amount compared to other softwoods. However I wouldnt use anything else for its strength to weight, straight grain usually, and resistance to rot. Not to mention how easy it is to work this timber. My main thought on building a boat, particularly if self designed, is to be really proud and happy with the finished product. The cost is forgotton on the day you launch your boat for the first time. :)
     
  13. BWD
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    BWD Senior Member

    It is douglas fir in the 2 strips with spots, WRC elsewhere.
    A warm spell hit after I flipped the hull.... The strips in the picture were fair quality to start, but apparently I ought to have precoated them.... live and learn....
    WRC definitely easier to shape, cut!
    Will keep the DF in my repertoire though, as some good, strong stock is available in my area. Check it out:
     

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  14. BWD
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    BWD Senior Member

    Thought I would revive this document, maybe a spur to completion.
    Many hiatuses, but...
    Softly, softly, building continues,
     

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    Last edited: May 5, 2008

  15. BWD
    Joined: Aug 2006
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    BWD Senior Member

    Hi all.
    Need some advice on the vaka, specifically on crossbeam fixation:
    Not wild about lashings.

    The crossbeams are to be 6 foot x 3" OD 6061 tube, 0.125 wall, which seems ok by my beamboy/seat of pants estimation, given the following:

    Typical crew weight 180lbs, positioned at most 4 feet out from vaka, and max. of around 350lbs if two are aboard.
    Vaka +rig weight ~140lbs.
    Lightweight Ama (hopefully under 30lbs, foam/glass)
    Ama displacement limited around 200lbs.
    Rig will be a 8-10m unarig (e.g. Hansen's "turbo" laser rig or similar).

    I've been thinking sliding the beams through tubular brackets across the deck, with a through-bolt at each gunwale for rigging speed and strength.
    Thinking of making up composite tubes of biax carbon and/or e-glass sleeving and bonding them to the main deck beams. I envision wrapping the Al beam in plastic for release and to give a few thou clearance, PVA, laying up a sleeve over it, mobilizing it, bonding on filler blocks of mahogany or fir, and then layingup a bigger sleeve over all to give a flat bottomed section to attach to the main deck beams. Or maybe I will just use cloth? Either way I think I could manage to build this way and still slide the result off the beam.

    I think the outer ends of the tube need the strength, while the inner 50% of it mainly needs to be strong enough to keep the beam from cracking it while being slid through during rigging. My guesstimate is 3-4mm of carbon in the outer 4-5 inches, around the gunwales, 1-2mm in the amidships part. i think this is likely excessive, but I have never made parts like this before....

    Advice on laminate design would be greatly appreciated, if anyone here has built something similar and wants to share.

    I posted first on SA, and was of course referred here.
    I know, I should read Boat Strength, hire an engineer, etc.
    But maybe I am jsut too stoopid.
     

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