Is it OK to place my daggerboard forward of center?

Discussion in 'Boat Design' started by mamessner, May 6, 2011.

  1. mamessner
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    mamessner New Member

    I'm building a small sailboat - an 8-foot dinghy (Flying Mouse from Ultrasimple Boatbuilding). The plans don't really specify how far back to put the daggerboard. I imagine that it's standard to put it equidistant from the bow and stern, but this would require cutting through one of the bulkheads and putting a somewhat fragile daggerboard box in the gap.

    Is it OK to place my daggerboard ahead of center, that is, just in front of the bulkhead? That would put it about 7 inches forward from where I imagine it should be on an 8 foot boat.

    The plans also give a rough guide for where the mast step should be, but says that it may need to be adjusted if the boat shows excessive lee or weather helm.

    If I move the daggerboard ahead, should I also move the mast ahead or astern to compensate?

    Thanks for any help!
     
  2. PAR
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    PAR Yacht Designer/Builder

    Place the daggerboard case directly under the CE. In fact, place the leading edge of the daggerboard case directly under the CE. No exceptions to these rules. On an 8' dinghy, you can adjust trim very easily with your butt, so the usual choice is to place the daggerboard case under the CE. I like the leading edge placement myself, for more casual sailing.
     
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  3. Fanie
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    Fanie Fanie

    On trimarans the daggerboards are usually a bit ahead of center. The way I see it, the daggerboard is the rotation axle when you tack. The furter forward the dagger board is the wider the rudder has to go and the slower it will tack. One factor of positioning I think is probably where is the hull's rotation point, a function of how it is shaped under water.

    If the daggerboard is a meter ahead of the hull's rotation point your rudder will have a hard time getting the hull and daggerboard to displace water to tack. The COF will have the same effect.
     
  4. PAR
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    PAR Yacht Designer/Builder

    It's an 8' dinghy Fanie. Placing the case forward of the CE is just asking for helm issues, again place the daggerboard case under the CE in an 8' dinghy. If it's performance oriented, then place the leading edge of the board under the CE.
     
  5. Fanie
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    Fanie Fanie

    In that case Par, a few terms he can use -

    Ahoy
    The first in a series of four letter words commonly exchanged by sailors as their dinghies approach one another

    Boom
    A Laterally mounted spar to which a sail is fastened, used during jibing to shift the sailor to a fixed, horizontal position.

    Calm
    Sea condition characterised by the simultaneous disappearance of the wind and the last cold drink.

    Hull speed
    The maximum theoretical velocity of a dinghy through the water, which is 1.5 times the square root of its waterline length in feet (approaching 0), divided by the distance to port in miles, minus the time in hours to sunset cubed.

    Life jacket
    Any personal floatation device that will keep a dinghy sailor who has fallen off a dinghy, above water long enough to be run over by other dinghy sailors.

    Sailing
    The fine art of getting wet and becoming ill while slowly going nowhere at great expense.

    Hope this helps :rolleyes:
     
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  6. boybland
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    boybland Junior Member

    Everyone else is giving the complicated answer, I will try for a simpler one.
    The answer to question is probably yes you can put it where ever you like within reason as long as the sails are positioned correctly relative to it (see more complicated answers above).
     
  7. PAR
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    PAR Yacht Designer/Builder

    I'm not sure what your reply is attempting Boybland, but no it can't go
    If the boat is expected to balance and steer reasonably, then the advice I've given above is the only reasonable choice. The CE is easy to find with a scale drawing of the sail plan at the kitchen table, with a pen and a straight edge.
     
  8. viking north
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    viking north VINLAND

    Well if you shy away from taking proper info from a qualified designer and builder how about from (a half *** designer)/ builder. By placing the leading edge of the dagger board case in line with the CE you are effectively placing your CE ahead of the CLR of your emerged hull and appendages(daggerboard) thus hopefully creating a little weatherhelm for a much better handling boat.--Geo
     
  9. keysdisease
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    keysdisease Senior Member

    What PAR and Viking say.

    To find the center of effort of your sail plan draw a line from each corner (head, tack, clew) to the center of the line (luff, leech, foot) opposite it. Where the three lines (Marconi rig, triangle) meet is the center of effort of the sail plan.

    Put the daggerboard under that spot as suggested.

    If you just put it where it's convenient you may very well end up with a whole bunch of lee of weather helm which is no fun at all any time the wind blows. In heavy enough air the boat may actually become uncontrolable without easing the sheet and slowing to a crawl.


    Steve
     
  10. PAR
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    PAR Yacht Designer/Builder

    Weather helm is a safety feature on small craft and a mandatory aspect of the boat's balance. This is simply because it's fairly easy to fall out of a small boat and weather helm will assure you aren't watching the boat sail away without you in it. Now, in a boat this size, just moving your butt a few inches can increase or decrease helm balance, in fact you can steer pretty effectively this way if you have to (or want to). As a rule (again) you want the boat's natural tendency to be to weather, so helm pressure, windward ability and steering response is normal.
     

  11. viking north
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    viking north VINLAND

    I should have said a much better behaving boat, a boat with manners, if you fall out she rounds up and like a good girl waits patiently until you swim to her, :)
     
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