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konajoe
Joined: 28 Feb 2010
Posts: 517
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 Posted: Thu Jan 29, 2015 2:58 pm Post subject: |
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Hmm. I think Dan just agreed with ME.
| DanWeiss wrote: |
The point is that most sails -seen very clearly in came sails- will appear to increase draft by increasing DH tension slightly as long as neutral OH tension remains. |
Folks seem to want to mess with the downhaul AND outhaul, then say that the change in fullness at the booms was due to downhaul.
So Dan. Cammed sail downhauled to mid recommended and 1 cm positive outhaul. Rig laying on beach. Pull the downhaul to max recommended. The cam rotates towards the clew, the sail gets flatter in the boom area, and the outhaul lines go limp. DON'T TOUCH THE OUTHAUL OR MESS WITH THE BOOM LENGTH. Put the rig on your board. Get out on the water and sheet out. Note that the cam is still pointed back towards the clew, the sail looks flatter in the boom area, and the sail is flopping around back where the clew is tied off.
Now, sheet in and power up. The sail fills, and puts tension back on the outhaul ropes. The cam rotates outboard. The position of maximum draft along the booms MAY have changed. But the distance between the leading edge of the mast (the front of the sail) and the clew grommet, is the same. The material didn't stretch, and no sail material was removed. |
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techno900
Joined: 28 Mar 2001
Posts: 4161
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| Posted: Thu Jan 29, 2015 4:38 pm Post subject: |
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Dan also said: | Quote: | | Increasing DH tension will reduce depth, as will increasing OH tension. The sail will respond to wind pressure and mast deflection in the same way, so using too little DH tension will eventually collapse the middle of the sail and allow the wind pressure to force the location of maximum draft back as the wind increases and bends the mast even more. |
This is what I think I have been saying. Maybe we all agree, but look at it in different ways. Since I have adjustable outhauls, I always set the OH to neutral, regardless of how much or how little I downhaul. The exception would be an on the water adjustment for upwind or downwind or gusts or lulls if needed to keep things balanced and appropriately powered.
If I DH too the recommended point, but see that the wind is picking up, I either rig another smaller sail, or I add a couple of cm of DH (and increase OH to neutral again). The sail has a shallower draft, the leach is loser and I have extended the sail's range to a higher wind limit. |
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isobars
Joined: 12 Dec 1999
Posts: 20935
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| Posted: Thu Jan 29, 2015 4:49 pm Post subject: |
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| techno900 wrote: | | If I DH too the recommended point, but see that the wind is picking up, I either rig another smaller sail, or I add a couple of cm of DH (and increase OH to neutral again). The sail has a shallower [and more stable, and lower, I submit] draft, the leach is loser and I have extended the sail's range to a higher wind limit. |
Don't those two sentences pretty much sum up and settle the past few pages from a practical point of view? If not, I'm going to stick my fingers in my eyes, hum "La La La La", and keep on doing it that way simply because it works. |
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techno900
Joined: 28 Mar 2001
Posts: 4161
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| Posted: Fri Jan 30, 2015 9:15 am Post subject: |
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| 10-4 |
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konajoe
Joined: 28 Feb 2010
Posts: 517
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| Posted: Fri Jan 30, 2015 1:26 pm Post subject: |
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| isobars wrote: | | techno900 wrote: | | If I DH too the recommended point, but see that the wind is picking up, I either rig another smaller sail, or I add a couple of cm of DH (and increase OH to neutral again). The sail has a shallower [and more stable, and lower, I submit] draft, the leach is loser and I have extended the sail's range to a higher wind limit. |
Don't those two sentences pretty much sum up and settle the past few pages from a practical point of view? If not, I'm going to stick my fingers in my eyes, hum "La La La La", and keep on doing it that way simply because it works. |
Pretzel logic!
I increased my downhaul. The outhaul lines went loose. So I increased my outhaul. Therefore, adding downhaul makes the sail flatter in the boom area.
This is even better. Some people like to smoke after sex. Therefore, sex causes lung cancer. |
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techno900
Joined: 28 Mar 2001
Posts: 4161
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| Posted: Fri Jan 30, 2015 1:47 pm Post subject: |
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Try it you may like it. My experience is with 3 & 4 cam wide luff race sails, you may find something different with what you use.
So what do you do when you get over powered on your sails, but don't change to a smaller sail? |
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ittiandro
Joined: 22 Nov 2009
Posts: 294
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| Posted: Fri Jan 30, 2015 8:39 pm Post subject: |
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| DanWeiss wrote: | Wow, lots of love flowing in this thread.
As we increase DH we will see location of the maximum draft move forward and down. We will also see the maximum depth of the draft decrease.
Now, back to tuning with OH and DH once in the intended tuning range, but now assume some positive outhaul. Increasing DH will decrease maximum draft and may even move it look like it moved back slightly! Increasing luff tension making the draft shallower right near the mast. Decreasing OH would then move the draft back while making it slightly deeper. Increasing OH would move the draft forward while making the draft slightly shallower.
Adding OH tension from neutral to positive at this point will increase tension along the seams radiating toward both ends of the mast, but most of the remaining action is around the boom area since that is where the maximum panel shaping exists. This increased tension is designed to decrease draft depth and usually force the draft forward. If the DH tension was now reduced, the relative OH tension would skyrocket, causing the draft to be very flat at the clew then suddenly become very deep in the front third.
Increasing DH tension will reduce depth, as will increasing OH tension. The sail will respond to wind pressure and mast deflection in the same way, so using too little DH tension will eventually collapse the middle of the sail and allow the wind pressure to force the location of maximum draft back as the wind increases and bends the mast even more.
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Excellent explanations!
I have always thought that a deeper draft would result in more power than a shallower draft, no matter where it is located
( the front or the back of the sail) . Your explanations seem to indicate, on the contrary, that a shallower forward draft ( profile) gives more power than a deeper one in the back ( towards the clew of the sail) . In other words, even though a positive OH would make the sail appear flatter, it would still make it more powerful, just because the draft is shifted forward, even though it is not as deep. Am I missing something here?
Given the fact that the sail profile (tension) can be controlled both by DH and OH in combination, what is the right way to maximize its power for really light winds? A relatively small DH first( for a fuller profile) and then a positive OH or the opposite : start with a relatively strong DH( flatter lower sail) and then releasing the OH?
Thanks for your elucidations
Ittiandro |
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konajoe
Joined: 28 Feb 2010
Posts: 517
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| Posted: Fri Jan 30, 2015 9:02 pm Post subject: |
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| Unfortunately, the explanations have been so good that, ummmmm. Nevermind. I'll let someone else tell you. |
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ittiandro
Joined: 22 Nov 2009
Posts: 294
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| Posted: Fri Jan 30, 2015 10:57 pm Post subject: |
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| konajoe wrote: | | Unfortunately, the explanations have been so good that, ummmmm. Nevermind. I'll let someone else tell you. |
You sound as cryptic as the Greek Oracle at Delphi ..You seem to hint at some kind of misunderstanding or incorrect statements, on whichever side they may be. It would be very informative to know...
I cannot help noticing though how much is debated or debatable in windsurfing! Beyond the fact that everybody agrees that to sail you need 1) a sail 2) a board and 3) some water, in all other aspects there seem to be as many schools of thought as there are sailors ..Or almost. Of course, I am being a bit paradoxical, but there is always a bottom of truth in paradox: in more than one respect, judging by the sometimes endless and very hot exchanges on the forums, windsurfing appears more as an art than a rigid technique.. |
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isobars
Joined: 12 Dec 1999
Posts: 20935
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| Posted: Fri Jan 30, 2015 11:10 pm Post subject: |
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| ittiandro wrote: | | everybody agrees that to sail you need 1) a sail 2) a board and 3) some water, in all other aspects there seem to be as many schools of thought as there are sailors . |
Some people argue the opposite, insisting that their way is the only acceptable way. Their loss.
Many of us have also sailed on ice, snow, dirt, grass, sand, pavement ... you name it. It's all good ... until you crash, and the differences become more apparent. |
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