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-   -   1st harmonic curve in job? (http://www.sailnet.com/forums/general-discussion-sailing-related/61368-1st-harmonic-curve-job.html)

toastchee 01-18-2010 08:53 AM

1st harmonic curve in job?
 
Tongue-in-cheek title but it is a way to describe what happened while sailing yesterday.

15-18 steady in Charleston harbor, port tack, heading upwind. Did not have jib trimmed in enough to have the proper curve in the entire sail area.

Logic says that it should have been luffing, but the sail settled into a steady shape with the leading edge curved inwards and the trailing 80% of the sail area with the correct curve outwards.

Can anyone describe why it was doing this? I was driving and I think it was still providing some drive to the boat.

-TC

Zanshin 01-18-2010 09:12 AM

Bernouilli effect from the mainsail kept the flow laminar and sucked in the foresail.

zz4gta 01-18-2010 10:15 AM

Trim in harder, Add forestay tension and halyard tension and see if it helps pointing and speed.

scottyt 01-18-2010 11:48 AM

its just a speed bubble. the wind was fast enough to push the bubble in but smoothed out enough to fill the rest of the sail. yes you could trim it out by sheeting a little tighter. on a main it can be caused by the turbulence off the mast, but it is okay on the main as it means the air is flowing nice and smooth.

hellosailor 01-18-2010 12:01 PM

Slot effect ("Bernoulli") from the mainsail causes an apparent wind speed increase and direction change, and sometimes "backwinds" the genoa when you really overdo it.

zz4gta 01-18-2010 12:16 PM

I'm a little confused. Are you backwinding the main or the Jib? A speed bubble doesnt' show up on a jib. I believe the OP is refering to the leading edge of the jib curling to weather.


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