simple amas for canoe-tri

Discussion in 'Multihulls' started by Owly, Jan 4, 2019.

  1. redreuben
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    redreuben redreuben

    Im not suggesting you build an entire Scarab, just use the float plans and pinch any other ideas that suit, like beam construction, he also has a sit in micro, all the plans are cheap $150.00 Au

    You should know by now Owly no designer has a design to exactly fit your requirements, your going to have to be adaptive and innovative by necessity Im just suggesting some feedstock for the mill.
     
  2. Owly
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    Owly Senior Member



    That's been obvious from the outset....... In any case, one of my criteria is budget. Why spend money on something I don't really need. These chined hulls are larger displacement than I need, probably built from more expensive material than the cheap 1/4" 3 ply fir marine ply I intend to use... most likely 3mm or 4mm, and more complex construction involving more panels and seams than my simple V hulls....
    I'm not sure that the chined hulls offer any concrete benefit for my application. I can achieve more displacement with a larger V... g1.25oing let's say with 12" sides, which would give me about 300 lbs displacement per ama to the gunnels. The 1/4" ply is stiff enough that I could get away with minimal internal support. With the two load bearing bulkheads being 78" apart, the sides curved in one plain, and only 12" tall, a seam along the bottom creating stiffening, and some plywood decking for a step... little if any additional support structure will be needed.... gunnels alone would probably be sufficient. At 23 pounds a sheet, and each ama taking 5/8 of a sheet plus the bulkheads and ply steps, that probably comes to close to 20 lbs of plywood. Add the fiberglass taping fillets & resin, the short beams (24" each total), a few light stringers on the fore and aft deck, the dacron cloth and dope, and paint, it should be possible to keep each ama with it's short beam well below 30 lbs. Heavier than I want, but it meets the fast and cheap criteria.
    I've also toyed with using blue XPS foam for parts of it, or even the entire amas. Blue foam with a glued on cap strip top and bottom becomes a pretty strong beam in one axis... I know of one ultralight aircraft that has a fairly long span full cantilever wing where the single spar is built this way... no glass, just foam and a wood cap strip, the foam replaced with filler blocks where needed... such as the root fittings. (Skypup)... Interestingly it has a superb safety record. I could see a 2" keel piece full length being the backbone, capped top and bottom, and additional sections added inboard and outboard, and stepped like a topo map, lightening holes cut where suitable... never know when you will get in one of those summer storms ;-).... A little fiberglass for abrasion and strength, and "rub rails" inboard and outboard that actually would serve as structural caps. Designed nicely and painted, nobody would ever know the construction material. I haven't mocked this up or calculated weight, etc. Epoxy would of course be needed to keep from dissolving it.

    H.W.
     
  3. guzzis3
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    guzzis3 Senior Member

    Well, GD's ply amas are essentially V shaped but he Vs the decks. They are slim and long and designed to immerse if necessary. He gives tremendous details on how to attach the floats to beams and beams to hull, how to mount a lee board, using secondhand windsurfer parts on and on. He's already sorted out all the stuff you will have to design as you go and the solutions are cheap. You will save more than the cost of the book.

    As for ply floats and chines you are correct. Seems to me to be a perfect case for tortured ply. The tornado plans are available free online somewhere. Scale them down. You will save on ply too potentially because you can use really thin stuff. I believe the gougeon book is available for free download and it has a section on tortured ply building.

    2c
     
  4. patzefran
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    patzefran patzefran

    If you scale down the Tornado plans to 1/2, you will halve the radius of curvature and exceed the capability oh the ply !
     
  5. patzefran
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    patzefran patzefran

    sorry , of the ply !
     
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  6. fallguy
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    fallguy Senior Member

    This is why the dierking foam is so great. Fully scalable..
     
  7. Owly
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    Owly Senior Member

    The Tornado hulls are compound curved... far more than I feel ply should realistically be tortured. Achieving that shape is from solid ply is beyond my capability / experience grade. Scaled 50% in 3 dimensions, the resulting float hulls would be about 13" depth by 10" beam at their max, by 10' long. These numbers are not exactly accurate, as I do not have real drawings to work from. I'm pulling eyeball numbers from this page: Tornado catamaran hull shape http://forum.woodenboat.com/showthread.php?184653-Tornado-catamaran-hull-shape
    It does indeed scale well........... Here is a snip from that page (below). It is easy to visualize a 15' canoe hull (square stern) set between those two hulls, which would be 10' scaled. There is actually a downloadable set of plans in PDF here: https://cdn.instructables.com/ORIG/FBW/B03O/9SMEP282LA0/FBWB03O9SMEP282LA0.pdf

    I like the shape, but it's not realistic for a quick easy stitch and glue IMHO. The bottom and sides curved in three dimensions is not what I want for simplicity. Take that basic shape and alter it to eliminate the curves except where the bow meets the keel, and of course eliminate the complex bottom shape, curved from the gunnel to the keel, and you have something buildable in stitch and glue. If I can knock it together in cardboard on my desk easily, it will build in stitch and glue ply.

    My inclination at this point is to increase beam over all to at least 11'. I've always intended that the amas be 12' long. Perhaps the sides should be 12" or more at their max dimension (laid flat), and the displacement shifted forward as on these hulls due to sail pressure.

    I'm not ready to cut ply.... obviously........ This is the idea stage. I won't be building from anybody's plans, as I said before, but it would be foolish not to use ideas from other designs. One rather mad idea I'd like to play with is a single airfoil shaped leeway surface that is steerable, rather than conventional leeboards. A trimaran does not heel a great deal, so two leeboards seem superfluous to me. Rob Denny uses fore and aft rudders on his Harry Proa designs..... obviously because he shunts rather than tacking, however the ability to steer the "centerboard" (which would be a "side board" that can kick back or retract), seems like it would have value for helm balance as well as tacking. The problem I've seen in past projects however is that too many "innovations" spoil the broth. They add problems to resolve, and stretch out build time. This is beginning with what is essentially a "throw away" canoe, and I'd like to keep project cost down to just a few hundred dollars. It seems that as with any project, the tendency is for cost to escalate.
    H.W.

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    [​IMG]
     
  8. Owly
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    Owly Senior Member

  9. Owly
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    Owly Senior Member

    A quick question about the table of offsets above..... The upper offsets have two figures.... anybody know what's going on there? for example the upper offset for sta7 is 420.6 and 414.6....... Which one is right, or are the sides asymmetrical above the datum line? It's a little bizarre that station zero is at 305mm instead of zer0 but that's no problem really. It's pretty clear.
    H.W.
     
  10. guzzis3
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    guzzis3 Senior Member

    Have a look at the wa'apa floats and beams. Dead simple, all problems addressed and perfect for your boat. One builder used shock cords to attach the floats to beams. It would be difficult to be simpler and he even manages to make them fairly pretty. I can't believe you can get all these books free now...
     
  11. patzefran
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    patzefran patzefran

    The offsets in line with vertical bars are from the original plans, the other figures aside are newer ones derived to get slightly fuller hulls and still complying with the rules.
     
  12. Owly
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    Owly Senior Member

    You wrote: "Dead simple, all problems addressed and perfect for your boat". Clearly your vision for what my boat should end up being and mine are quite different. For one thing, I plan to have solid, permanently attached "wings", creating a platform 6'6" fore and aft by 6' width, with the canoe itself forming an opening in the middle that is 3' wide at the widest point. These wings then will be 18" at their narrowest point (the widest point of the canoe). The beams will form the forward and aft edges to these surfaces, the edge of the canoe where the gunnels originally were, the inboard edge, and a light plank on edge, the outboard edge. This will all be permanently attached, tabbed into the main canoe hull with fiberglass tape. It will provide the camping platform, as well as comfortable seating that will be dry, and will be made of 1/4" plywood. This is not a take down setup, temporarily added onto an otherwise functional canoe. This is a heavily damaged canoe that was caught by the wind, and sustained a number of impact damage points that will need repaired, and the gunnels were literally ripped off. A $200 used fiberglass canoe 25 years ago, much worse for the wear. The mission is sail camping. the Wa'apa amas are far less displacement than I want for this application. A proa is very different, and the ama is always held to the windward side ( pacific proa ). It carries no weight, and needs little flotation, as it usually flies while sailing.... the beams carry the hiking seats.

    The closest analog of what I intend to end up with is the Strike 16 illustrated above. The wings, beams, and floats all come very close to where I intend to end up. Look back on the previous page. My wings will not be as deep, but the overall area will be wider, but the total beam of the boat will be less, the amas will not displace as much, the whole boat will be far lighter, and will lack the forward shelter, though a dodger would be a nice addition. Since the canoe bellies out considerably in the center to a full 36", I'm thinking that I may lap the wing decks inboard about 6", which would allow for two people to sleep, one on each deck with 24" of flat surface. Two 6.5' by 2' side decks... not generous, but sufficient.

    The challenge of course is to keep the weight down, and maintain sensible proportions. 15' is not very much boat to work with.

    H.W.
     
  13. Owly
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    Owly Senior Member

    Thanks... that makes sense........
     
  14. Owly
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    Owly Senior Member

    I've been building scale models of floats from linerboard (about the same as shoebox material). The design I like best so far has it's maximum section 24" aft of the bow, which is curved. At that point the side section is 12" laid flat. It slopes gently in a straight line toward the gunnel which is straight from bow to stern. At the stern it would measure 8", but about 12" forward of the transom, it begins an upward slope of 3" to avoid any transom turbulence by raising the transom by 3" so it should always be out of the water... or nearly always.

    In making these linerboard models, I simply score the linerboard deeply with a box cutter along the keel line, and fold the sides up, then tape the bow to hold the curved surfaces together. I'm thinking of doing something very similar on the real thing, and will do a test on some scrap 1/4" plywood to see if it works. The procedure will be to lay the hull sides would be laid atop one another and simply taped with fiberglass tape using something like West Systems G Flex or Total Boat FlexEpox,, or one of the other flexible epoxy resins. The hulls would then be opened out propped at the desired spread, filleted and taped, and bulkheads cut to fit. The sides being straight in one axis, it should not be difficult to make bulkheads to fit. The keel of course would receive several layers of cloth for abrasion and strength on the outside.
    The desktop model looks very nice. Spreading it produces an attractive sheer line. These amas should give me a bit over 200 lbs displacement if they were flat decked. They will not be flat decked. 200 lbs displacement means I can step on an ama without submerging it. The next question is where the step decks on the amas should be. Logically right next to a beam, but where there is flotation..... However as they will be used for boarding and debarking, perhaps they would best be aft...perhaps from the rear beam to the transom. This will be the shallowest draft area. I envision beaching and boarding from the stern, and the aft corners make sense.


    H.W.
     

  15. Owly
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    Owly Senior Member

    Was doing some weight calcs, foam versus 1/4 ply, including a layer of cloth and resin on each side, the foam being 1" XPS insulation foam.... The weight savings is stunning! I plan to use ply for the hulls still, but the side decks , each of which will be at least 6' by 2' , and partially overlap the gunnels of the canoe, can be foam and glass, as can many other components such as bulkheads. The beams can be foam core with wood cap strips top and bottom, as per Skypup wing spars. Foam is cheap... and more important light. Glass and epoxy add up..... but weight is a huge issue.

    My ama design is vaguely similar to the Tornado ama in the drawings above, but mostly straight rather than curved along the bottom, and max displacement is further forward. This will take two sheets of plywood. I'm tempted to go with the 4mm Okume for weight reduction.... which would add another Cnote to the cost 13 lbs per sheet versus 23 lbs. The 1/4 will give more strength, which means less internal structure (weight).... the difference not counting the internal structure would be 15 lbs per ama.. that's significant, but half or more of that savings could easily be gobbled up by internal structure....... I like simplicity, but I also like light weight. This boat will not be "light" when done, and I'm not getting any younger.

    H.W.
     
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