Pointing Ability, Long Keel vs Dagger Boards etc

Discussion in 'Sailboats' started by LSaupe, Nov 2, 2010.

  1. tspeer
    Joined: Feb 2002
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    Location: Port Gamble, Washington, USA

    tspeer Senior Member

    RHough has it right. The equilibrium leeway angle and boat speed will adjust themselves so the total hydrodynamic force equals the total aerodynamic force. The aero force is under the control of the crew. The hydro force is determined by what's needed to oppose the aero force. If the hydro force is anything else, the boat will be accelerating - either changing its speed or carving a curved course through the water.

    What is lift and what is lateral force depend on the leeway angle. If the boat is stalled out and moving straight sideways (hove to, for example), there will be a sizeable lateral force, but little or no lift because the velocity vector is nearly at right angles to the keel and the lateral force is being provided by drag. If the leeway angle is zero, then all the lateral force is being provided by lift.

    The statement, "You can have more lateral force from the sails than lift from the keel, what you cannot have (to my knowledge) is more lift from the keel than lateral force from the keel. " is technically correct because the lateral force is a lift*cos(leeway)+drag*sin(leeway) kind of transformation. But it misses the point of the original question.

    And actually, you can have more lift than lateral force if leeway is negative. That would be the case if you had an overly cambered asymmetrical board or an overly gybed centerboard.
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