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Why a sail that pulls does not necessarily have power
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flaherty



Joined: 01 May 1997
Posts: 425

PostPosted: Wed Aug 28, 2019 6:03 pm    Post subject: Reply with quote

Apparent wind plays into this, also. doesn't it ? I'm fascinated when sailing how apparent wind feels. As you go faster and faster, I've always noticed how it looks windier ahead as your moving. Then jibe and feel the real wind, not as strong. One of the many aspects that make windsurfing such a joy !
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boardsurfr



Joined: 23 Aug 2001
Posts: 1246

PostPosted: Wed Aug 28, 2019 6:06 pm    Post subject: Reply with quote

A few things come into play: drag, sail efficiency, how high the draft is, and how far open you can or have to use a sail. Some race sails can feel extremely light when powered because they are very efficient and have very little drag. That's one reason race sails tend to be larger than freeride sails - you need a larger size to get the same sideways pull.

With wave sails, you often have to choose between how much power you want, and how much "off" you want. Very powerful wave sails tend to have deeper profiles and keep some profile even when depowered.

Freestyle sails try to be very powerful while also going fully "off". One trick to accomplish this is by having the battens stick far past the mast when not powered. They also have tighter leeches and a higher center of effort. That give the sail more leverage and hence power, but can make it a bit harder to sail, at least until you're used to them. But a good freestyle sail lets you pick how much power you want freely, from perhaps 125% down to 0% (compared to a freeride sail of the same size), and everything in between.
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spennie



Joined: 13 Oct 1995
Posts: 971
Location: Thousand Oaks, CA

PostPosted: Thu Aug 29, 2019 12:22 pm    Post subject: Reply with quote

OK, I haven't fully read every post in this thread so far, but I have some time to kill, so......
There's quite a few factors that affect a sail's ability to work properly. First is design & construction, of course. A windsurf sail is a foil, not a parachute, as has been stated here already. If it's rigged poorly, even the best sail will handle poorly.

If you've been told that a baggy sail has more power, that's a gross over-simplification, which could lead you to believe a sail laying on the boom (little or no outhaul) is going to generate more power. That will cause it to pull, but not forward, because you're not creating the proper foil shape.

A lack of proper downhaul will make your sail "pitch" forward, because it's generating power in the top of the sail instead of twisting properly. I've been helping people with under-downhauled sails for 27 of my 29 years of windsurfing, but I'm afraid they'll never learn.

For heaven's sake, people, read the specs on the bottom of your sail, buy a metric tape measure and learn to rig properly! If you don't know what a properly rigged sail is supposed to look like, consult your sailmaker's website, talk to the good sailors at your spot, and/or get as close as you can to factory specs & experiment from there!

Downhaul instructions vary by maker, but a good rule of thumb is to set your extension one mark higher than the number on the sail, so you have room to play with. If the sail's spec says 447, use a 430 mast and set your base to 20, instead of 18. Pull until the top 2-3 panels are loose, more if it's gusty.

Outhaul is usually measured from the back of the sail at the boom ("clew") to the front of the mast, or possibly the center. If you're not sure, try pulling until it's just off the boom for power, more to smooth it out if jerking. A sail that's over outhauled will tend to try to move around in your hands and not generate very much power, again, experiment & learn!

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dllee



Joined: 03 Jul 2009
Posts: 4987
Location: East Bay

PostPosted: Thu Aug 29, 2019 12:46 pm    Post subject: Reply with quote

I see TOO MUCH downhaul more of a problem.
We've been drilled since 1987 to loosen the leech.
Now, a 175 lbs rider needs a 6 meter sail to plane solidly in breeze of 15-25. And spends lot's of time slogging.
Rig a 7.0?
Or a 5.0 with barely tight leech and outhaul 1/2" from the inside of the boom arm?
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spennie



Joined: 13 Oct 1995
Posts: 971
Location: Thousand Oaks, CA

PostPosted: Thu Aug 29, 2019 2:42 pm    Post subject: Reply with quote

dllee: Your comment sounds like sophistry, it seems logical but doesn't really make sense. The actual comment could read "use a 5.0 that handles poorly and is trying to jerk out my hands, or rig the proper size and have a smooth handling enjoyable sail".

So many sailors are obsessed with size! (no jokes, please!) I remember in the Delta flying downwind on the river having an incredibly good time, past rows of sailors sitting on shore, the "Say no to 6.0" crowd. Bigger sails aren't evil, they can be wonderful if properly rigged.

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dllee



Joined: 03 Jul 2009
Posts: 4987
Location: East Bay

PostPosted: Thu Aug 29, 2019 3:11 pm    Post subject: Reply with quote

You got it wrong.
An underdownhauled sail is totally stable, since the wind is really too LIGHT for that sail size.
When the wind comes up 5mph, just try to drop into the water, pop the mast base off the foot, downhill to spec..which is easy because everything is wet and you're jacked, and slide it back together.
I sail with NO loose leech half the time, no problem when wind is slightly too light for sail chosen.
Wind changes.
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spennie



Joined: 13 Oct 1995
Posts: 971
Location: Thousand Oaks, CA

PostPosted: Thu Aug 29, 2019 3:28 pm    Post subject: Reply with quote

I guess we'll just have to agree to disagree: I disagree with you, and you disagree with every sail designer and pro sailor on Earth.
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mac



Joined: 07 Mar 1999
Posts: 16208
Location: Berkeley, California

PostPosted: Thu Aug 29, 2019 3:47 pm    Post subject: Reply with quote

Spennie--I agree completely. I've done the same thing in Berkeley for about 30 years. Offer to help a sailor tune their sail. It is true that a modern sail of say 7.0 meters is not much more "powerful" than a 5.7 of the very old days. But the top speed of the modern sails, and the ease of handling is light years better.

A well rigged sail shouldn't just "pull", and it should be rigged to spill wind in a big gust.
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dllee



Joined: 03 Jul 2009
Posts: 4987
Location: East Bay

PostPosted: Thu Aug 29, 2019 7:15 pm    Post subject: Reply with quote

When there are no big gusts, why spill wind?
When your 6 meter sail meets 30 mph gusts, max downhill for sure. But to get that 6 meter sail to plane in 16-19, no looseeech is needed.
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dllee



Joined: 03 Jul 2009
Posts: 4987
Location: East Bay

PostPosted: Thu Aug 29, 2019 7:44 pm    Post subject: Reply with quote

Now at Berkeley...
16-23, what do YOU rig?
Soften on 4.4.
Ming 5.0.
Roger 5.2.
All little guys.
Kevin K, at 195 lbs before a wetsuit, would choose 4.4-4.8 on a 95 liter board.
Now what size would YOU rig?
Me, 5.0 with moderate downhaul OR 4.2 with tight leech Or 6.9 slalom fully dowhauled.
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