Lift from centerboard and rudder?

I have heard that "centerboard and rudder can also lift" twice. One case was a commentator of world cup laser medal race mentioning that in laser, sailers do not bring up the centerboard too high because the centerboard can create lift. The other was Paul Goodison's LASER HANDBOOK: p. 70: "Remember that the rudder and daggerboard will also create lift."

What "lift" do these mean? Will that is a force which can move the boat forward? This sounds a little odd to me because both sides of the centerboard and rudder are symmetric.

Thank you very much in advance,
Toshi
 
If a foil section itself is symmetric is not the point; if you move it through the water at an angle then the flow around it is asymmetric and creates lift. It's a force perpendicular to the centreline, and while it doesn't by itself move the boat forward, it opposes the sideways force from the rig and the resultant vector of it all points forward. Of course, the deeper downwind you sail, the less you need it. It's interesting though, that the top sailors these days keep their boards quite deep down even on the running legs.
 
Thank you very much, LaLi. I think I now I understand this. So the effective lift from the centerboard seems to cause positive feedback: The faster the boat goes, the more lift created, and the more effectively boat goes, ...
Perhaps this could also explain that the more the boat heels leeward, the more sideways and then more heels also.

This may also explain why the top sailers tend to keep centerboard down... If they heel the boat rather windward, then the board may also create actual lift for the boat, like the moss sailer does?
 
This may also explain why the top sailers tend to keep centerboard down... If they heel the boat rather windward, then the board may also create actual lift for the boat, like the moss sailer does?
If you want to exert a vertical force on a boat, one that may even lift the hull(s) out of the water, you need to have a foil at a vertical angle to the centreplane of the boat. The Moths do it with T-foils, multihulls with curved, J- or L-shaped ones. Just heeling a "normal" boat like the Laser to windward actually has the opposite effect (which the rig cancels out though).

I've assumed that the reason for having the centreboard most of the way down on the offwind legs has more to do with facilitating more accurate steering rather than getting lift for lift's sake. But I will be studying this more next year :D
 
Yes I also noticed the trend is more towards the centerboard being keep lower down when going downwind.
 
Not just the blades, but the hull also creates lift. I may be wrong here, but the hull may generate enough lift when going fast than you can partially raise the centerboard to decrease drag. Of course you will probably need to hike harder.

When going downwind, I sometimes keep the board down if the waves are causing side-to-side rocking. Helps with that whole I-don't-want-to-death-roll thing. Not necessarily fastest in terms of boat handling, but certain faster as in keeping the pointy end up.
 
i keep my board down when its windy just because its more stable. you wont lose boats with it down but you will when you death roll. when the winds light to medium i pull it up. same with reaches anywind
 

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