Analysing Upwind Performance

[Jammen]

In a mono and a tri you have one keel/daggerboard with only on end free against the water. On a cat you hav two end surface wich makes the daggerboard "look" shortern then thay are.

This is the same reason we are not flying biplanes today and one reason twin rigged boats nerver will performe either.

//Calle

[truemorc]

So we can feel confident that the lift vs drag is the primary issue in the original question on pointing? And mostly the Hydro end of it in this case?
I just want to make sure I have it right. Emphasis on primary...For those of us who are a little less advanced. Thanks.

[HeloDriver]

Hate to be the proverbial wooden nickel, yet I would like to resolve the above issue regarding maximizing L/D for optimum windward performance and seek clarification. Is indeed max L/D our target?

Originally Posted by RHough

Sailing to windward is L/D pure and simple. You need low L/D to go to weather, the higher the L/D the higher the boat points.

If you can increase lift without increasing drag you point higher. If you can decrease drag at the same lift you point higher.

If your boat doesn't point as high as another, your L/D ratio is lower than the other boat's.

I may have misunderstood from the 2004 Seahorse: Hollom/Oglesby articles 'Go with the flow' that for a given planform, low CDp in conjunction with an proper stall angle was emphasised over L/D.
Though Max L/D appears to be a simpler resolution!

Originally Posted by truemorc

So we can feel confident that the lift vs drag is the primary issue in the original question on pointing? And mostly the Hydro end of it in this case?
I just want to make sure I have it right. Emphasis on primary...For those of us who are a little less advanced. Thanks.

There was a similar yet maybe not totally resolved discussion a while back in the thread entitled "Keel design issues" Keel design issues. And like truemorc above..layman's explanation appreciated.

[tspeer]

Originally Posted by HeloDriver

Hate to be the proverbial wooden nickel, yet I would like to resolve the above issue regarding maximizing L/D for optimum windward performance and seek clarification. Is indeed max L/D our target? ...

No. Maximizing the L/D of the rig alone, or even maximum aerodynamic L/D of the rig+hull is not sufficient. You must minimize the apparent wind angle, beta, which requires the combination of aerodynamic and hydrodynamic drag angles be minimized.

One factor that enters into this is the hydrodynamic lift from the hull depends on the lift from the rig. The L/D of the hull is limited by the amount of lift demanded by the rig. In offwind sailing, the L/D of the hull is very low because it has drag but is not required to produce much lift. This isn't a fault of the hull design - it follows from the sail trim and point of sail.

In upwind sailing, if the maximum aerodynamic L/D is below stall, it may pay to trim the rig for maximum lift instead of maximum L/D, even though the aerodynamic drag angle will increase. The added lift can improve the hull's L/D and reduce the hydrodynamic drag angle more than the loss in the aerodynamic drag angle, and improve performance.

In general, for the kinds of boats we're talking about, the windage is so high that the rig will stall before it reaches maximum L/D. So there's benefit in improving the maximum lift as well as the L/D of the rig alone. But the really big gain may come from reducing windage.

[HeloDriver]

Originally Posted by tspeer

No. Maximizing the L/D ... is not sufficient.

Does that statement apply to the keel as well?