Why my boat can't move forward in strong wind???

Discussion in 'Boat Design' started by redmapleleaf, Jul 7, 2008.

  1. redmapleleaf
    Joined: Jul 2008
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    Location: Boston

    redmapleleaf Junior Member

    Hi all,

    This weekend was my boat's maiden voyage. When I took it out the first day, the wind was light (about 5-6mph) and I was able to sail downwind as well as upwind without any problem. Then, on the second day when the wind really picked up (over 12mph), I thought it would have made the boat sail even faster than before. To my surprise, upwind sailing (sailing close haul) was terrible. The boat was not able to gain an inch on the upwind and instead just moving side way or being blown back by the wind (and wave).

    Do you know if there is some fundamentally wrong with my boat design?

    Please see the attached pictures for an idea of how the boat look like. Some info on the boat:

    1. length: 16'
    2. outrigger beam: 8'
    3. sail area: 52 square feet
    4. submerge area of centerboard: 1 square feet
    5. submerge area of rudder: .5 square feet

    Will it help if I add more sail area or centerboard area?

    Thank you for your help.

    Attached Files:

  2. longliner45
    Joined: Dec 2005
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    longliner45 Senior Member

    maybe your boat is at its limits ,,I dont see any kind of a keel,maybe im wrong,,,,,nice looking boat ,,but everything has a limit ,or zone of effitiancy,longliner
  3. the1much
    Joined: Jul 2007
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    Location: maine

    the1much hippie dreams

    what part of boston?,,i swear ive seen that shoreline before,,,,,,,when your sitting in ya boat,, where does ya bow sit?,,or,, where at is your waterline.,,and before you get to much hope,,,im not REALLY gonna be of any help to ya ;)
  4. lazeyjack

    lazeyjack Guest

    just kwikkly, one I dont think you have enough center board and two I think your sail is, well an awful; shape, send a pick on the beach with your sail in the close hauled position please
  5. marshmat
    Joined: Apr 2005
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    marshmat Senior Member

    Hi redmapleleaf,

    I'm trying to figure out, firstly, just how your boat works. It looks almost as if it sails as an Atlantic proa (ama to leeward) on port tack, and a Pacific proa (ama to windward) on starboard tack, but still has a distinct bow and stern that do not switch places when tacking (which would make it more of an asymmetrical cat than a proa). Is this correct?

    Regarding your problem with going to windward, it sounds like you're getting plenty of thrust from the sail (although the sail shape could definitely be a lot better), but the hull's not interpreting that force the way you want it to- it's sliding sideways, rather than forwards. The solution would seem to be more lateral resistance- what do you have now for a daggerboard / leeboard / centreboard?
  6. Meanz Beanz
    Joined: Jun 2007
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    Meanz Beanz Boom Doom Gloom Boom

    Sail looks crook, more board will help... first up I would play with rig balance and see what it does. Rake the mast back a few degrees at a time until you get some, but manageable, weather helm. See what that does for the uphill performance...

  7. PAR
    Joined: Nov 2003
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    PAR Yacht Designer/Builder

    1.5 square feet of appendages isn't enough area, though just speculation considering the limited amount of information available. A reasonable guess would be 4 to 5 sq. ft. as a starting point.

    I've never seen a boat do well to windward without a fairly healthy amount of weather helm. This can be affected by several design elements, none of which we have information about.

    I'll second the comments Matt has made concerning the set of the sail. In bigger wind strengths, you'll have much difficulty controlling the leach on that square topper.

    Other issues could be entry shapes, lee bow wave formation, location and amount of "lead", effective lateral area, CG/CB relationship, frankly the list is quite long. Can you provide spec's for the design? Lines and sail plan?
  8. lazeyjack

    lazeyjack Guest

    you could always add a small jib too
  9. the1much
    Joined: Jul 2007
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    the1much hippie dreams

    shouldnt the sail have more "puff" room,,haha,,,,like i mean not so tightly stretched?,, give the wind a place to "dish",,,< as you can see,, i jus built the boats,, didnt want nothing to do with rigging, and hated to deliver the things,,hehe ;)
  10. redmapleleaf
    Joined: Jul 2008
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    Location: Boston

    redmapleleaf Junior Member

    Hi all,

    I initially want to design a 'super stable' boat with two floaters, one on each size giving it a beam of about 14'. I guess you can call it a trimaran.

    Well with two pantoons, I then found that it is a bit difficult to dock the boat with the pantoon on its side therefore I removed one of them. This make it an asymmetrical cat like Matt has noted. I was also hoping that this would make the boat a little lighter and move faster.

    In my second picture you can see the centerboard sticking up for the shore landing. It shows how much centerboard the boat has. The sail is made out of white tarp cut to a triangular shape so it is not of very high quality. Since I saw a number of other DIY design used tarp before so I was hoping that it would work for me also.

    My boat is in Halifax, NS and I am now back to Boston to work so I can't take any more picture of it to show you. I am going back there in two weeks. I'll increase the centerboard area and add a jib to it to see how it will perform. I'll let you know more about it then.
  11. alan white
    Joined: Mar 2007
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    alan white Senior Member

    More lateral plane needed, as mentioned. I'd double what you've got and you'll do fine to windward. I checked an old design of mine---- a proa---- and 16 ft at that. I'd calculated 2 sq ft for the free area of the leeboard. Rudder must have been at least 1 sq ft. Though I never built her, she was designed with those areas.
    I'd imagine there's a formula for sq ft sail area to sq ft lateral plane in Gerr's 'Nature of Boats".
    You'll also have problems going to windward in heavy air if your sail has too much draft, meaning you want the sail flatter when it pipes up, otherwise you'll induce more drag than lift and the boat will drag to leeward (and heel much more).
    Also, try sailing full and by, meaning easing the boom a bit (away from centerline). You'll actually make better progress doing this in some boats. Put the boom at maybe 15 degrees off. Try a vang too, or rig something to pull the boom down on the leeward side.

  12. redmapleleaf
    Joined: Jul 2008
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    Location: Boston

    redmapleleaf Junior Member

    Attached is a little more information on the boat dimension.

    Attached Files:

  13. tspeer
    Joined: Feb 2002
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    tspeer Senior Member

    I would guess your board needs to be much deeper.

    Going upwind is all about lift/drag ratio, and the best way to improve that is to reduce drag. The drag due to lift on the hull & foils goes down by the depth squared, so a little deeper can be very significant. For example, if you make the board 40% deeper, you cut this source of drag in half. If you double the depth of the board, you cut this source of drag by 75%!

    You need to add a batten to your sail to hold out the corner at the head. A couple of battens farther down on the leech wouldn't hurt, either.

    Technically, the proa aficionados would classify your boat as a "tacking single outrigger".
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  14. lazeyjack

    lazeyjack Guest

    Hello Tom Speer,
    Its nice to see you post again!!
    Well at least we are in agreement here
    I well remember, as lad of 13, sailing the P class, which all NZ,ers cut teeth on, and from that boat came many world champ dinghy and round world sailer, I remember the PLATE, which was what we called the c board, and its importance
    You should get your weight well forwards too, sailing this boat and as Tom said, battens, one about 2 feet down from head of sail, with soft spot third way from luff and tied in tight,
    Ah those wonderful days of youth

  15. redmapleleaf
    Joined: Jul 2008
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    Location: Boston

    redmapleleaf Junior Member

    Hello Tom,

    You have raised an interesting point about the lift/drag force versus the length of the centerboard. It seems that you have some kind of formula for calculating this number. I am very much interested in learning about these formula as it would guide me to build a better boat.

    I know that the aerodynamic of sailing is a very complicate topic but I have to believe that there must be some simple 'rules of thumb' to help us common designers to build a reasonable boat. Here are some of the things that I thought it would be helpful to know:

    1. give a sail area, windspeed, angle of attack, how much lift force can we expect. Just maximum and minimum.
    2. given a centerboard area, shape, how much side force can it sustain? Let say this is a really thin board so that one don't have to worry about the foil shape performance.

    Knowing 1 and 2 then I guess one can calculate the resulting force vector to determine if the boat will move forward or not.

    BTW, I read this page on the physics of sailing (http://www.physclips.unsw.edu.au/jw/sailing.html) and they indicated that the resulting force on the sail is due to 'change in the wind velocity' and the Bernoulli effect is only secondary. However, I read some other sites and they only mention of Bernoulli effect. So what is the main sailing force here???
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