Forces on a boat

Discussion in 'Hydrodynamics and Aerodynamics' started by rolexer, Oct 29, 2012.

  1. rolexer
    Joined: Oct 2012
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    rolexer Junior Member

    Hello!
    This is the first time I am using this forum.
    I have a project where I have been tasked to find out what forces affect a sailboat. Both the sail and the hull in the water.
    Want above all know what happens on the hull in the water.
    Is this a project any of you would be interested in? If so I would like to hear from you with any comments about the approaches you might think I would get to the goal.

    Hope to hear from you!
     
  2. gonzo
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    gonzo Senior Member

    The answer would take a whole library. However, the basics are flotation, skin resistance, wave resistance, wind drag and heeling moment. These are all interconnected and in continuous flux.
     
  3. rolexer
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    rolexer Junior Member

    Ok, does anyone know if there are good websites or books where this is explained from a broader perspective.
    Have not found anything on the net ....
    Can someone explain in more detail how the VPP (Velocity Prediction Program) works?
     
  4. daiquiri
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    daiquiri Engineering and Design

  5. DCockey
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    DCockey Senior Member

  6. philSweet
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    philSweet Senior Member

    There is, in fact, a fairly canonized presentation of this. The forces due to the air acting on the hull are decomposed into vectors parallel and perpendicular to the direction of apparent wind. Thus a sail's lift is in the direction perp to the apparent wind and aero drag is parallel to apparent wind. Hydro is treated the same way. The forces are with respect to the vessels course, not it's heading. The difference being leeway. One will usually transforms the aero forces into the hydro axis. This results in a drive force and sideforce caused by the aerodynamics. Now you can calculate moments. You can then use another transform to relate these to the hull's orientation. This could include consideration of any number of factors, ie pitch, yaw, roll, heave, sway, and surge. You will find it to be a nomenclature nightmare if you try to work the problem in all six degrees of freedom. Understanding the forces in the plane of the horizon is easy enough. But a decent VPP takes a lot of sophisticated math to properly evaluate.

    In addition to the steady state performance, the ability to reef and change the twist in a sail is at the very heart of sailing, and VPP's need to account for this at the very start.
     

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  7. DCockey
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    DCockey Senior Member

  8. rolexer
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    rolexer Junior Member

    Thanks!
     

  9. RAraujo
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    RAraujo Senior Member - Naval Architect

    I thing "Sailing Theory and Practice" from C. A. Marchaj is a very good reference.
     
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