Fabric Centerboard

From resistance, drag, not from lift.

-Will

 

Not all drag is from resistance. The rest of the dynamic force by a foil when lift is vectored out is backwards.

 

Curious. I had always understood that lift was calculated to be perpendicular to the cord of the foil. Other than resistance, I had neven understood there to be another vector to factor in. Drag, as I learned it in my university physics classes, has two basics component: cross-sectional area and shape + surface area.

I'll have to read up on the subject.

-Will

 

It's the same with sails but another direction. Beating most of the sails aerodynamic forces are perpendicular and smaller portion forwards making the driving force. The keel works the same way working with an angle to water flow and thus fluiddynamic forces. Most of it of course is perpendicular but smaller portion backwards, like backing jib when hove to..

ps. recommend: Marchaj: Aero-Hydrodynamics of Sailing

 

the standard definition of lift is perpendicular to the direction of the approaching flow, not the chord of the foil. Drag in the direction of the approaching flow.

A keel or centerboard does not provide a net force in the direction of travel unless the vessel is in a current moving across it's direction of travel.

 

Well, that makes sense when breaking out the force vectors. Defining lift to be up, basically, in the case of an airplane. But, does that account for the sum of all forces derived by flow around a foil shape? Excluding straight surface drag, of course. Or is that unreasonable to do, as well? Is it, any force vector perpendicular to flow is called 'lift', and any force in the direction of flow is drag, and any force counter to flow would be... drive? Then a force perpendicular to flow, in the opposite direction of lift is... gravity? (Except it can't be gravity, as force is not an element of gravity any more).

There is a lot to digest.