JAXAshby wrote:

dougie, the tip vortex comes about because the pressure on the windward side of
the sail is greater than on the leeward side. The greater pressure tries to
make it to the lower pressure. the air on the heavy side rolls over the aft
edge of the sail in the easiest possible manner, which includes going up as
well as back. This makes for the vortex as the aft edge of the sail meets the
forward edge.

A little slower, Jax... Navvie is taking notes...

You have got part of the explanation of tip vortex, so far so good. But if what you
say is all there is, then why are there not a series of vortexes all along the
trailing edge instead of just at the tip? Of course, when the flow is just
starting, that's true, but after flow is established there is just a vortex at the
tip.

Another thing to account for is vertical pressure distribution.





having a main sail downwind of the jib does not cause the jib airflow to stop
trying to go from high pressure to low pressure. The vortex generated causes
turbulant air from the jib to screw up the airflow across the main. moving the
top of the jib lower than top of the main just causes the jib vortex to hit
more of the main.

okay?

But that doesn't answer the earler question... the differential pressure across the
main is going to interfere with (and suppress) the tip vortex from the jib. Got it
so far? That means that energy lost through the jib head tip vortex will be less.

Now, is that energy gain for a frac rig greater or less than the gain a masthead
rig gets from not having the jib head tip vortex disrupting flow across the main?

Folks, I think Jax *might* begin to actually grasp the question this time.... any
bets?

Fresh Breezes- Doug King