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Thread: Outrigger question

  1. #1
    Join Date
    Jun 2012
    Location
    Montreal, QC, Canada
    Posts
    46

    Default Outrigger question

    I am currently building a sailing rig for my canoe with includes outriggers. These are made from a small sailboard that I cut in half lengthwise and then shortened at both ends, curving up from the thin outside edge to the line where I cut it in two. These pieces are then set on edge to become outriggers (the centerline of where I cut the board becomes the top of each outrigger). I largely eliminated the front part of the sailboard with normally curved upwards and kept the flat, back end to make these. One thing though is that the sailboard had an almost flat bottom and a curved top, thickening to over 3 inches in the middle. Set on edge, this creates an outrigger with one slide flat and the other side with a curve, like an airplane wing vertically set in the water. Having seen the discussion about leeboards and "lift" (more like "side push" because of their vertical orientation) I was thinking that my outriggers would have a similar effect for the part that is under water. With that in mind, could this be a hidden benefit? An undesirable side effect? I was thinking of putting the flat side on the outside and curved on the inside, which would cause the wing effect to push towards the canoe, since the leeward side outrigger would normally be the one in the water. This would act like the leeboards, counteracting leeward side drift.

    Any thoughts on this? All ideas, discussions and theories are welcome!

  2. #2
    Join Date
    Nov 2010
    Location
    grange over sands, cumbria
    Posts
    930

    Default

    The lift from the outrigger will only happen if it has an angle of attack as it runs through the water. This will increase the drag from the outrigger, and its shallow depth will not be very efficient at creating lift. In light winds it will not be depressed enough to have any effect. Will you be using a leeboard also? This will be much better at preventing leeway and improve upwind performance. I like the idea of using the cut down sail board though. What length, width and depth is the shape that you have made? A photo would be good. How are you planning on fastening it to your beam?

  3. #3
    Join Date
    Jun 2012
    Location
    Montreal, QC, Canada
    Posts
    46

    Default

    In my mind, any angle of attack (as opposed to being parallel to the axis of the canoe) would have a steering (ie: rudder-like) effect, not "lift" in the sense of an airplane wing where the longer flow path around the curved side creates a higher flow rate and lower pressure area, causing the flow on the flat side to push or lift. All the outriggers I've seen so far appear to be symmetrical, so some steering effect could be created by modifying their angle of attack. Makes for a separate and interesting discussion too... The threads I've seen so far regarding this sometime discuss possibly adding toe-in (setting the front ends a bit closer to the canoe).

    In this question I'm talking about actual "sideways lift" created by the asymmetrical shape. This would create a pushing force closer to the center of the outrigger, as opposed to a turning force, especially if the mounting point is close to the center of the canoe. As you hinted at, I suspect that the usually shallow depth that it will sink in to will cause it to normally have minimal effect. The outriggers are very light and very bouyant. They will be about 7 feet apart. Yes, I also will be using leeboards. As for mounting, I will not have a single beam but rather two parallel beams, 19 inches apart. The front one is where the mast will be and the rear one will be at the middle of the canoe. This is a 16 foot canoe. Having two beams means that I can easily force the outriggers to be parallel or not to the canoe. I can also mount the outriggers (they are about 54 inches long) more or less aft of the center. This is where experienced people (ie: from this forum!) might have good suggestions and ideas. The beams will attach to the top of the outriggers with stainless steel bots and wing nuts.

    I should be taking some pictures in the next few days, making this discussion easier. Thanks for the reply!

  4. #4
    Join Date
    May 2007
    Location
    Deepest darkest Wales
    Posts
    3,891

    Default

    All sailing craft make leeway when going to weather - this is what provides the angle of attack for fin keels, leeboards, dagger boards, centre boards and kiribati proas alike.

    The idea of using an asymmetric hull form to provide lift and thus resist leeway - is not new either - the best selling recent example is probably Hobie Alter's "Hobie Cat" - sold by the thousand and has armies of loyal fans.

  5. #5
    Join Date
    Jun 2012
    Location
    Montreal, QC, Canada
    Posts
    46

    Default

    Well, I have finally completed my initial build of this project, and tried it out today. First of all, I know that my sail (using a sail, mast and wishbone boom from a windsurfer) are not in the best configuration. The sail is rather large (66 sq ft) and is set very high due to its design for a windsurfer. Still, I figured that in a very light wind, I would be able to try it out. I plan on getting a smaller sail, setting it much lower, etc eventually. As you can tell, the crossbeam is actually more like a truss, holding the outriggers, leeboards and mast all in one piece. It looks large but is made of aluminium and is very light. It weighs 26 lbs and I can easily pick the whole thing up with one arm. As one joker put it: "it looks like a truss off the space station". The idea with this project was to not modify anything on the canoe...everything attaches with wing nuts.


    Rudder assembly




    Leeboard mount




    Beam ready for transportation. When mounting on the canoe, the leeboards are first swung over the end, and then rotated to horizontal for launching the canoe.





    Beam mounted on the canoe






    Actual first sail earlier today, in light wind

    http://www.youtube.com/watch?v=Po8BP...ature=youtu.be

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