Outrigger location - affect on sailing

Discussion in 'Boat Design' started by Eciton, May 10, 2017.

  1. Eciton
    Joined: May 2017
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    Location: Virginia

    Eciton Junior Member

    16' canoe, 8' outriggers. how does putting all three centers inline compare with having the three bows inline?

    this would be flat water lake, some larger river/bay sailing.

    outriggers would be flown or just barely touching water

    thanks! outriggerlocation.jpg
     
  2. rwatson
    Joined: Aug 2007
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    rwatson Senior Member

    The positioning has a HUGE effect. Your picture of having the amas out of the water all the time is a fantasy. When you tack or get an unexpected gust, even on 'flat'water, the placing of the pods has a big effect, either slewing you around into the wind or forcing a nose dive depending on conditions. When you are just sailing the leeward pod will be forced into the water and affect the steering of the main hull, and change the fore/aft centre of effort. I would recomend you look into some proven designs to start with.
     
  3. messabout
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    messabout Senior Member

    It is also a matter of concern that the wakes from one hull to the other of the three are of some concern. All that is a matter of the speed of the hulls but it is worthy of some consideration.

    The section shape of the amas is a determinant of how much influence the ama will have on the centers of lateral resistance of the entire three hull assembly. In short, your question leads to more complex questions involving the center of effort of the sail and the wind direction and a whole mess of other things. Not to make this a federal case, but you need to provide more detailed information about the general configuration of your boat.
     
  4. Eciton
    Joined: May 2017
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    Eciton Junior Member

    appreciate the replies. i have seen production boats with either configuration hence my question.

    sailing canoe with approx 35-40sqft of main sail mast is approx 30'' aft of the bow.

    primarily i'm concerned about stability because my two sons are smaller and I dont want to flip the canoe. its is not a high performance boat and we will not be breaking any speed records. initially i had thought to use much smaller flown outriggers like on the solway dory canoes but figured perhaps bigger might be better if I can rig up a trampoline system ala the hobie island kayak my boys can goof around with a bit more room.
     
  5. messabout
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    messabout Senior Member

    Give some thought to the position of the cross beams. The beams will intrude into the interior space of the main hull. Probably a more rigid set of cross beam to hull connections would be with centrally located amas. That is only because the canoe is wider at the attachment points. The amas are merely stabilizers and they will work in either configuration as long as the whole assembly is fairly secure.

    The position of the sail with respect to the rest of the boat is a matter of importance. Imagine that you have the boat and the amas all assembled and have it afloat. Now tie a small rope to the side of the boat and pull it sideways. You would need to pull sideways at some point that would have the whole assembly move directly in line with the place where you pulled on the rope. The boat assembly would not try to turn if you have located the right place........what we have done is find the static center of lateral resistance (CLR) of the boat. You must have the rudder fixed at center position when doing this stunt. Alas that location might change when the boat is in motion. We can calculate the center of effort (CE) of the sail with a bit of geometry. A typical sail like that of the Optimist pram has about 36 square feet of area. Its CE is about 36 inches aft of the mast. The trick is to get the CE and The CLR to work favorably together. The additional trick is to guess how much lead to give the combination. "Lead" is a term that describes how far ahead of the CE the CLR is to be. That means that the CLR will be ahead of the CE by some amount......maybe eight percent of the waterline length or somewhere in that ball park.

    You can not move the CLR but you can move the mast position so that you do have some lead. It should be obvious that you can not depend on the 30" average dimension that you see on other canoe rigs. You have to experiment to get it right. Therefore if you use a movable bridge that supports the mast, you can tinker with the mast position until you get it about right.

    If you use the ama forward configuration the CLR will be somewhat forward of the place it might be in the case of the centered amas. Forgive me for making this sound complicated. I am clumsily attempting to explain some of the details in an elementary way. Well, at least you will know about some of the details that affect the way the boat sails.

    I have not even mentioned that you will probably need some lee boards to keep the sail from pushing the boat sideways and of course the fore and aft location of the lee boards will have a large influence on the CLR of the whole assembly. You might get away without boards if you let the amas be wet and hard chined so as to provide some lateral resistance.

    Are we having fun yet?............. Hang in there you can do this.
     
  6. garydierking
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    garydierking Senior Member

    Having the amas as far forward as possible will reduce the chance of a diagonal capsize. Note that all modern racing trimarans have them close to even with the main hull. Indonesian double outriggers often have them extending forward of the main hull.
    Gary
     
  7. messabout
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    messabout Senior Member

    That is a good observation Gary. Entirely valid for powerful trimarans with lots of sail. In the case of the 16 foot canoe, with such a tiny sail, the prospect of doing a diagonal pitch pole or burying a lee bow would not be a hazard,..... short of a force eight weather event.
     

  8. Eciton
    Joined: May 2017
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    Location: Virginia

    Eciton Junior Member

    appreciate all the replies, lots of info to consider. I'll upload a sketch later on for some review.

    My original thought was just to mimic the hobie island tandem setup on the cheap. since i have a canoe and dont have an extra 6k for the hobie. ;) It looks like the island is bow even vs center even. as most of you guys mentioned it seems most are bow even, if the amas are hitting the water, centered if its just a safety net.

    looks like im leaning more towards trimaran territory vs safety net.
     
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