Canoemaran? CanoeTri?

Discussion in 'Multihulls' started by Owly, May 23, 2017.

  1. Owly
    Joined: Oct 2016
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    Owly Senior Member

    I've started a canoemaran project from an old fiberglass 16' canoe I've owned many years, but was damaged when loaned to friends.... basically wrecked by wind. This was a hundred dollar canoe 20 years ago!

    The project will involved cutting off the stern, which I already have done, and installing a transom with a kick up rudder.

    Two 1/4" marine plywood bulkheads will be installed to carry the loads from the akas to the hull.

    Akas will consist of two components. An oak 1x6 in the center that will extend out to about 66" more or less, and a folding outboard section attached to the amas, which will be foldable by removing one bolt for trailering. Total width will be about 10' with amas down in position.

    It will have two small side decks, between the two inboard akas, each being about 16" wide, the akas forming front and rear combings, and an additional combing along the outer edge. The decks will also be 1/4" marine plywood, fiberglassed on the bottom side and tabbed into the side of the canoe where the gunnels were, and cut out to match the existing contour. These decks will be about 7' long

    The area forward of the front aka will be "decked", with an access hatch that it more or less water tight, using a combination of plywood next to the aka where the access hatch is located, and aircraft type dope and fabric forward to the bow.

    The stern will provide seating for paddling with a kayak paddle, and be clear of the boom.

    The mast will be supported at the forward aka.

    I plan to build the amas using extremely light bulkheads except where the akas attach, using wood strip and fabric construction.......... Again aircraft fabric and dope, with the bottom fiberglassed for abrasion, and a plywood step area on top adjacent to the side deck for beaching sideways. Sit on one side deck and push the opposite ama up onto the beach. They will just kiss the water when level, so one's weight shifted to one side should easily lift the opposite ama into the air.

    I'm debating using blue foam instead of plywood, but it will need to be epoxy sealed due to solvent sensitivity.......... Anything I can do to keep weight down.

    My big concern is mast strength. I would like to put a larger amount of sail on this than would normally make sense, to allow it to sail in extremely light winds. It will be a low aspect ratio sail for obvious reasons.

    The idea with this boat is to be more than a Sunday afternoon sailor. It's all focused on being useable as a camper on some of the large local reservoirs with a tent over the boom. With the sail reefed, and the boom lifted with the topping lift, a decent interior space could be created. I'm not a weekender, as I've never had a "job", and these huge reservoirs are very quiet on week days, and some well over 100 miles long with lots of quiet coves along the shore.

    Ideas anybody? The project is moving forward all be it slowly.


    H.W.
     
  2. upchurchmr
    Joined: Feb 2011
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    upchurchmr Senior Member

    Good luck with the project.
    Here is another forum for canoe sailing, although, most here do not use ama's like you are describing.

    Current typical skin of frame boats do not use aircraft dope/ system. Its an expensive system that is not really necessary. Ordinary house paint will work just fine.
    Aircraft fabric is also expensive and light weight. A typical SOF kayak will use 8oz Dacron that is not heat set. Several sources, I buy mine from George Dyson.

    Have you ever tried to fiberglass SOF Dacron? It is done by one builder, but he covers the entire kayak hull - using the Dacron skin as a mold. I don't know how you would do only the bottom.
    Personally, I have built both SOF and strip planked kayaks, and I'd want to use strip plank for the ama's due to the higher bending stiffness and strength. They are also pretty light. For a 16' ama I'd guess less than 20#. Of course that's just imagining how I'd design the amas.

    Oak is very heavy for the fwd aka. Even older designed small trimarans use fir in a hollow configuration or even just a 2x4. These were designs with hinged outer sections as you describe.
    You really need more depth than width for an aka. A 1x will have lots of bending even though oak is very stiff. If the aka was 2x3 for the same weight the stiffness would be around 4x.

    How much flotation would you be looking for in the ama? Equal to the boat + sailor +equipment? Or just a part of that?

    Sounds like fun. I've daydreamed about something similar for a long time, but never started. :)

    Marc
     
  3. Owly
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    Owly Senior Member

    Marc:
    I plan to have the amas fairly high displacement due to the high sail area I hope to carry. My original thought was to strip plank the amas using very thin douglas fir, kind of like a cedar strip canoe I built many years ago. As the amas will be a full 15 feet long to match the final length of the canoe, they will end up having a lot of displacement....... more than I need. The key is keeping weight down. I had in mind to have a v bottom, and the forward end fairly bulbous for more displacement forward than aft. The displacement of the amas will be sufficient I hope to "fly the main hull" and the opposite ama without submerging. I haven't yet done the displacement calculations. The amas will have at least a shallow keel.
    Aircraft dope is pretty cheap actually in the generic types. Most commercial fabric has sizing, which is a lubricant used in the manufacture, which may not be compatible with dope. You make a good point about adhesion between the resin systems used for fiberglass and aircraft dope. Dope would not be necessary with heat shrunk material, though it is very tough and makes a seal. I'm not confident of resin retaining it's integrity. Normally a dope with powdered aluminum is used as a UV barrier.

    I'm not concerned about the 1x6 flexibility for the simple reason that it is incorporated into a structure consisting of a plywood deck attached to the bottom, and a light weight combing along the outer rim. It really can't twist as a result. Good point about weight. Ordinary Douglas Fir is about half the weight, and quite strong. The decks will lock things in, as far as fore and aft bending loads. The outboard portion connected to the amas themselves will only be about 2' long or so. The reason for the 1x6 is to have a fairly high combing to shed water coming over the bow. I'm looking at using the outboard combing a gutter system with drains at the outboard corners. The lee side will probably take water in the form of spray, and the V formed by heel angle will make a natural gutter. A flap along the leading edge will prevent water from entering there.

    I just checked and Wicks Aircraft offers 1.7 ounce uncertified dacron aircraft fabric in 71" width for $7.77 per yard............ That doesn't add up very fast in price compared to fiberglass. It seems from everything I can find that Epoxy resin will adhere to doped fabric fairly well....... epoxy is expensive, about $100 per gallon shipped here, but a gallon will go a LONG way.

    I've come up with many ways to build the amas, I just have to decide on one.

    H.W.
     
  4. upchurchmr
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    upchurchmr Senior Member

    I buy 8oz Dacron fabric for about $6/ yard - about the same width as I remember.
    You don't want any dacron with sizing. Maybe you were talking about the glass.
    I also bought 50yds of 6oz glass for just over $4/yd. Nice stuff, I'm using it now on a kayak.

    Aka's don't twist much, they bend, because there are two of them separated by a good distance.
    If there was only one there would be lots of twist.

    What do you need a V-bottom on the ama for?

    SOF does not resist the bending of an ama very well, there is no shear strength due to the typical construction. When you drive the ama down in the water you are going to get lots of bending fore and aft, and between the akas.

    When building a SOF kayak, I attach the deck to a frame around the cockpit by bonding with Epoxy. It has worked well for 7 boats, never failing.
    Recently, when I recovered two boats, I needed to peel off the Epoxy joint. Really was not very difficult, it was certainly consistently stuck, but it did not take high force or heat or anything else to remove.
     
  5. Owly
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    Owly Senior Member

    Considering the fact that there will be about 7' between akas on a 15' ama, the bending loads will be fairly well supported. 8 ounce cloth is far heavier than I want, though 1.7 ounce is really too light. I can get 3 ounce from Aircraft spruce for $4.35 a yard, and that's about right. It's about what you would cover a Cub with. The heavier the fabric, the more dope or whatever it absorbs. The fabric has very little function on the sides and top, hence my idea of using glass on the bottom.

    V bottom so the ama "digs in" and resists leeway, but I've got a better idea for that, roughly based on an ama design by John Marples. It's gradually coming together in my mind at least. I may end up using lee boards, but I'd rather the amas "dug in" when it heeled. It might be interesting to make the akas in such a way that one could adjust the toe in / toe out of the amas to see what worked best.

    H.W.
     
  6. upchurchmr
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    upchurchmr Senior Member

    Looking forward to what you end up with.
    I hope you will continue with the detail and photos when appropriate.

    Marc
     
  7. Vantage475T
    Joined: Aug 2016
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    Vantage475T Vantage475T

    Hi,

    I have prevously made a heavily modified CLC Sport Tandem with their Sailrig Mk3 so broadly similar idea.

    I have trampolines on the beams so my wife can sit out and keep it flat along with an RS200 jib to get better balance. Tramps have been great as otherwise with both of us in the middle the leeward float buries and with simple vertical brackets it digs in and really slows us and skews us round. I will fair in the brackets also to improve this further.

    Some pics and vids here:
    Small Trimaran Projects In The UK - Kaymaran Skiffmaran Anythingmaran http://www.smalltrimaran.co.uk

    and just the vids on youtube:
    Kay Maran https://www.youtube.com/channel/UC3evMZcrGGGCWwonCBHOuHQ

    Various differences as it is nearly 22ft long, 11ft long low volume floats and 11ft wide and the main hull is a kayak not a canoe.

    The biggest problem is the slow tacking due to length and light weight - the leeboard position took quite a while to get it right. If you have skegs in the outriggers I think it will tack very slowly compared to having leeboards. You need to get this right as otherwise might be frustrating for you.

    I am also just rebuildig my leeboards to make them bigger and mount them both sides - ripped the last leeboard off as forces are gettign quite high so going to integrate them into the trampoline frames.

    The rudder needs some more beefing up as well.

    The mast is very flexible and I have put some oose stays to keep the shape better and it goes much faster across wind ranges - leaving the mast completely freestanding was not great with the sail losing shape horribly.

    I would be interested to see some pics as it develops.
     
  8. Owly
    Joined: Oct 2016
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    Owly Senior Member

    I've see photos of this boat before............ very nice work!! I'm planning much larger displacement floats, as they will be the full length of the main hull. The season here is short, and it's cold water country, hence the solid side decks with the beams and an outboard combing between them providing significant protection. About 7' between the beams (akas), and over 5 and a half feet from outboard combing to outboard combing, part of the idea is that I want to be able to camp aboard on some of the huge reservoirs we have in the area that are lightly used on week days, and virtually unused before memorial day and after labor day except on weekends.
    A friend suggested two sets of lee boards, one forward of the other for trim reasons........ a good idea I think. My plan was to have them fold up under the side decks. The other interesting possibility I'd like to play with is a single forward set of lee boards, and two kick up "trim rudders", one on each outrigger (ama). They would be designed such that they were mostly out of the water until the boat began to heel, would be airfoil shaped, and would be adjustable both for angle and depth with the idea that they should be able to be finally set for optimal performance and left alone. One one tack, one would be well into the water, and the other pretty much lifted clear.
    I'd love to have a yawl type mizzen aft of the transom. The rig I want to use is more or less similar to the rig on the small trimaran shown here: Little Tri Sporting a Split Junk Rig | Small Trimarans http://smalltrimarans.com/blog/little-tri-sporting-a-split-junk-rig/ But will be built along the lines of the aerojunk, where the battens are not part of the sail, but a cage surrounding it. Here is a photo of the system on a larger rig: The Junk Rig Association - Illustrations http://www.junkrigassociation.org/Tech-Forum-Illustrations/48020129 I won't go into the details of why I want to use this rig, but this boat will be a test bed for a much larger boat.

    I've been toying with ideas for outrigger shape, and have been thinking of an outrigger shape that when heeled over will have "bite", sort of related to the concept of the chine runner. Here is a blog with some drawings and discussion of chine runners. The idea being that in a flat attitude, they will not be providing any "bite", but heeled over, they will resist leeway. I'm also playing with ideas for construction methods and materials that will keep the weight down and cost under control, yet make construction easy.

    H.W.
     
  9. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    It may be a problem with my browser settings but I am not seeing a link referred to by Marc about a forum or Owly about a blog.

    You have obviously put a lot of thought into this project, I don't know if you saw this discussion in the small trimaran under 20' thread starting at post 149 Small trimarans under 20' https://www.boatdesign.net/threads/small-trimarans-under-20.43650/page-10 in this case an all SOF trimaran but may be relevant.
    Regarding the chine runners, with the float 5' from the centre, the change in the angle of heel of the float may not be sufficient to create the effect.
     
  10. upchurchmr
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    upchurchmr Senior Member

  11. Tiny Turnip
    Joined: Mar 2008
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    Tiny Turnip Senior Member

    Hi Owly.
    Two more sources for you.

    The Open Canoe Sailing Group:
    and their facebook page:

    and Solway Dory, a UK company who make sailing canoes, and the accessories and equipment needed to convert conventional canoes into sailing canoes.

    A few things I would note. Most OCSG members use relatively short amas, and aim to keep them clear of the water when possible; they are used principally to prevent capsize in a gust.

    They almost all use single leeboards, and the leeboards and rudders are high aspect ratio foils. When tacking, the boats swing round the 'pivot' of the leeboard easily.

    I would be concerned that with amas as long as the main hull and no leeboard, tacking might be problematic.

    My own boat is a special, a purpose built trimaran that is not stable without the amas, so mine are larger and longer than the norm. the main hull is 16 ft and the amas are 10ft, with a rounded cross section and a fair amount of rocker. (as does the main hull) They each provide 200 litres of buoyancy, which gives considerable righting moment to counteract the forces on the rig. The lack of keel effect from the amas is no problem because the foils are high performance.

    Because the Solway Dory rigs are unstayed and the sails unbattened, they reef easily by unclipping the boom and spinning the mast.
    Many of the boats including my own, use ketch rigs, which allow them to carry more sail lower down, on the unstayed masts.
    Best of luck and energy with the project.
     
  12. Owly
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    Owly Senior Member

    Tangent of 15 degrees is .2679 tangent of 10 degrees is .176 Multiply that by 60 inches and you get a vertical movement at 15 degrees 16" from level to heeled 15 degrees, and a vertical movement at 10 degrees of 10.5" from level to heeled 10 degrees. At 5 degrees of heel this is 5.25" of vertical motion 5 feet out from center.
    Assuming the amas just kiss the water at rest, that would seem to be plenty of vertical change in the heel ranges of normal sailing to get some "bite". Famed trimaran designer Dick Newick once had an experimental ama design with the outboard surface a concave "half moon" shape. It was said to work, but at the expense of displacement.
    What I'm proposing to do is build my amas on a central 1/4" marine plywood backbone canted about 20 deg off the vertical. This backbone would have formers attached to both sides with longitudinal wood strips over the formers. On the outboard face, these formers would begin several inches above the bottom edge, leaving a "runner" which would quickly submerge and have bite. The face of this "runner" will never reach vertical, and will create a V along with the surface above it, that should produce a good "bite" when heeled.
    I can see this in my "mind's eye", but I don't describe things very well verbally. Start with your ama as nothing but a piece of plywood canted 20 degrees. Then flesh it out with flotation, leaving a portion unfleshed. Am I making any sense at all ;-(

    H.W.
     
  13. latestarter
    Joined: Jul 2010
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    latestarter Senior Member

    This was the only aspect I did not see at once, the rest of your descriptions are clear.
    I am with you now, I was visualizing a chine runner as on some microcruisers that need a large heel angle to be effective.
    Yours is "pre-heeled" so offering a vertical surface as soon as it submerges.
    Just for clarity, is the bottom of the ama canted towards or away from the main hull?
     
  14. Owly
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    Owly Senior Member

    The piece of plywood is more or less a vertical backbone that extends from the bottom of the ama to the top, and it is tilted with the top 20 degrees or so toward the boat, and bottom outward. The bottom of the ama is of course also tilted outward as is often seen on trimaran floats. The inboard and outboard sides of the ama are obviously not identical........ a very asymmetric structure...... function rules here rather than form, and the functions are first to provide flotation and stability, and second to resist side draft (leeway).
    I'm terribly tempted to build the entire ama from blue extruded polystyrene foam, except for the central backbone of plywood. It could be glued up in layers like a topographical map using epoxy, hollow on the inside, and faired on the outside....... then glassed on the bottom and epoxy coated and painted on the rest.
    I'm a ways off from actually building the amas, so I can toy with all kinds of ideas...........

    H.W.
     

  15. upchurchmr
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    upchurchmr Senior Member

    If you want ama shape to contribute to resisting leeway, the flat side needs to be on the outside, the rounded faired side should be on the inside.
    You should go look at a Hobie catamaran - those boats basically invented the shape and 10's of thousands of boats produced proved it.
    Blue styrofoam is c**p for properties, and plywood does not resist bending well on edge.
    Of course you can make anything thick enough and add enough glass/epoxy skins to hold it together.
    But it will be heavier than you need.

    20 degrees is way too much also.
    Do a layout of your boat an see what the angle of heel is when the ama is immersed. That's all the angle (dihedrial) you need
     
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