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Re: Running Flat?
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Ed Conley
Thanks Howard and Wayne for your explanations and reference material.
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I had observed that my "Fish-clone" was much slower when in a tack or reach course where the gooseneck orientation allows the sail to lie against the mast thus changing the sail shape. In one lake in particular I could half my time spent (seems like it anyway) tacking to the larger part of the lake just by planning ahead of time which side of the boat the gooseneck would be facing. One of the first observations about my "Fish-clone" shortly after purchase was that the daggerboard has been repeatedly damaged and refinished to sand out smashed spots and, as repair allowed, the leading edge of the daggerboard was finished to a sharp edge or point along the plane of the board. With the daggerboard involved so much in the potential lift of the system its shape must be very important. Wouldn't a rounded blunt leading edge allow for better off axis flow without producing turbulent drag? Again with no local real or racing "Fish" to view I am operating in the blind. Dose anyone have a plan with dimensions on it for a good daggerboard design? I am planning a trek to the Vanguard dealer in Oakland sometime in the future but would like any words of wisdom form other "Fish" owners. Thanks again! Ed -----Original Message-----
From: Howard Bishop [mailto:bishop2398@...] Sent: Tuesday, March 25, 2003 6:27 PM To: sunfish_sailor@... Subject: RE: [sunfish_sailor] Running Flat? Don't know if this helps or not, but if all else fails, think of the last time you flew a kite. Remember how much harder it pulled on the string when it was nearly overhead compared to when you first launched it (straight downwind)? It's something like that. A slightly more technical attempt at an explanation follows. The thing that makes sailing anything other than straight downwind is the dramatic shear, both in terms of velocity and viscousity, of the two fluids involved (air and water). There are a couple of other useful things to remember: 1) in other than a dead run, the centerboard produces useful lift orthoganal to the direction of the boat's travel (lift in other directions may be produced, but it is un-useful and should be counted as drag). 2) the dynamics of a sail while reaching or pointing are incredibly different than that of one running. It is the difference between a gyrocopter and a helicopter, or between a parachute and a hang glider. with those thoughts in mind, we go on: When running straight downwind, the theoretical maximum speed is equal to wind speed. period. When bearing off slightly, we could, in theory, retain the downwind vector, but add the new, slightly off-wind vector. Depending on the amount of wind, the efficiency of the sail, and the amount of lift generated by the daggerboard, there is some theoretically optimal angle at which to sail. Bear in mind, that as one speeds up on a beat or reach one introduces yet a third vector which may in fact *increase* the amount of lift the sail produces. At some point the lift vectors generated by the sail and board (note: these vectors will differ in both magnitude and direction- the difference their lateral components is your leeway) will achieve some stasis with the drag vectors of the system (both hydro and aero dynamic)and the theoretical max speed is acheived. Howard __________________________________________________ Do you Yahoo!? Yahoo! Platinum - Watch CBS' NCAA March Madness, live on your desktop! Yahoo! Groups Sponsor ADVERTISEMENT If you do not wish to belong to Sunfish_sailor, you may unsubscribe by sending an email to: sunfish_sailor-unsubscribe@... Please do not send unsubscribe requests directly to the group. USEFUL ADDRESSES Post message: sunfish_sailor@... Subscribe: sunfish_sailor-subscribe@... Unsubscribe: sunfish_sailor-unsubscribe@... URL to egroups page: Your use of Yahoo! Groups is subject to the Yahoo! Terms of Service. |
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