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ittiandro
Joined: 22 Nov 2009
Posts: 294
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 Posted: Sat Jan 24, 2015 2:41 pm Post subject: |
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Thanks for your input
I have read the thread http://www.iwindsurf.com/forums/viewtopic.php?t=29450&start=10 making reference to my case. Yes, a wrong mast could be the culprit ( in addition to technique.) .
As stated elsewhere, in response to one of your previous questions, my mast is a 460 cm constant curve GunSails mast ( 55%). Probably a hardtop would help to optimize the low wind end by allowing a tighter leech. This would make sense, also because my 8.5 is a Severne and Severne make their sails for their masts, which are HT.
On the other hand, I fear that what I gain with a HT mast ( a tighter top-end leech) I may then lose because the small DH would be insufficient to pull out the batten for proper rotation. ( I know this from experience). This is why I had thought of shortening the batten by 1-2 cm at the luff-end ( and then restitching the pocket) so that they won’t stick, even with a small DH).
I agree that to “macrotune” sail power (as Isobars says ) the key is increasing the sail size, but I am reluctant to go to a still larger sail, because 1) the cost of buying more equipment and 2) The sail would become too big for comfort ( weight and uphauling). This may be no more than a personal idiosyncrasy, but nevertheless a real one.
I also tend to agree with U2U2U2 when he says, that “there will be a point where down/outhaul adjustments will have diminished return, the sail will not perform”, but for the moment I have to make do with what I have and do some more experimenting.
Windsurfing is also an ART afterall and some times a bit of creativity and openness to unconventional solutions can help.
Ittiandro |
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adywind
Joined: 08 Jan 2012
Posts: 665
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| Posted: Sat Jan 24, 2015 3:04 pm Post subject: |
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| Sigh...one of those soft 80s longboard sails is just what you are looking for IMO. |
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jingebritsen
Joined: 21 Aug 2002
Posts: 3371
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konajoe
Joined: 28 Feb 2010
Posts: 517
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| Posted: Sun Jan 25, 2015 10:08 am Post subject: |
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Wow! All kinds of interesting things in this thread. Some geometry issues. And sail exhaust???
First, Ittiandro, where did you ever hear that more downhaul will give you more power? There's not a single rigging guide that will say that. Maybe you had your sail so under-downhauled that you needed to add downhaul just to get the downhaul to within spec range? So to be clear, you need to add downhaul to your sail until it is close to the minimum downhaul recommended for your sail. Once within range, adding more downhaul will de-power the sail.
No. A floppy leach is not needed to plane. If that were true, nobody would have ever planed before there were sails with floppy leaches. Folks who use sails that were designed to be rigged with tight leaches have no problem planing. Under-downhauled sails that were designed to have floppy leaches will still plane, but will have the rotation issues that you've seen.
Now, the geometry problem. If you have a sail outhauled to the end of the booms, and then, you let off some downhaul, have you really made your sail fuller in the boom area when under wind load? I don't think that's possible |
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techno900
Joined: 28 Mar 2001
Posts: 4161
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| Posted: Sun Jan 25, 2015 10:25 am Post subject: |
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Bottom line, if you aren't trying to plane (say 8 knots of wind), just cruising and want more power/speed (say 7 knots now, trying to gain 10 knots of speed), it's possible to tune your sail to get more speed. However, you may never see 10 knots of speed even with perfect tuning.
So, how to get moving at 10 knots of speed? One, find more wind; two, work on sailing skills (there are a number of things you can learn to help with board speed); three, get a bigger sail!!!!!!!!!!!!!!!!!!!!! Your concerns about a larger sail are valid, you just have to consider what you really want to achieve. Remember, you will never get a gallon of milk out of a quart bottle.
All the numbers above are somewhat subjective. Just an example of how you can resolve your dilemma. |
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isobars
Joined: 12 Dec 1999
Posts: 20935
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| Posted: Sun Jan 25, 2015 10:40 am Post subject: |
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| konajoe wrote: | | If you have a sail outhauled to the end of the booms, and then, you let off some downhaul, have you really made your sail fuller in the boom area when under wind load? I don't think that's possible |
I do it all the time. Because I usually must cross a nasty wind shadow to get to the good stuff, I usually set my boom length and OH to the chord length I'll use on the outside, slack off the OH for extra draft and power across the shadow, then drop into the water and snug up the OH when I'm looking down the barrel of the wind. The difference in sail fullness at the boom stares me in the face from two feet away, indicated by whether and where my sail touches my boom. The power difference is equally obvious as measured by planing very quickly when I hit the "release button" on an adjustable outhaul when allllllmost planing. |
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konajoe
Joined: 28 Feb 2010
Posts: 517
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| Posted: Sun Jan 25, 2015 11:42 am Post subject: |
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| Nope Isobars. You misread my post. Downhaul, not outhaul. |
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ittiandro
Joined: 22 Nov 2009
Posts: 294
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| Posted: Sun Jan 25, 2015 1:09 pm Post subject: |
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| konajoe wrote: |
First, Ittiandro, where did you ever hear that more downhaul will give you more power?
No. A floppy leach is not needed to plane.
Now, the geometry problem. If you have a sail outhauled to the end of the booms, and then, you let off some downhaul, have you really made your sail fuller in the boom area when under wind load? I don't think that's possible |
If you mean that a floppy leech is not needed( or perhaps not even recommended)for LIGHT WINDS planing, I fully agree. In fact, I can’t remember where I stated so categorically that a floppy leech is ALWAYS needed! This may be an extrapolation from what I (and PeconicPuffin, too), said elsewhere in this thread. For one thing, I always tend to be more keen to keep the DH to a minimum and the leech tighter!
I did not say that a floppy leech gives more power. I agree with you, it does not. What I mean is that when you have POWER, i.e. when you plane in moderate to strong winds (as most people do, when planing) a strong DH ( =floppy leech) is required to spill excess winds and counter sudden gusts. In fact, as you yourself say, even the prevailing conventional wisdom of modern windsurfing, which is all about speed and planing, ALWAYS recommends a strong DH in moderate to strong winds.! One even reads that if you can DH by hand, it is probably not enough!
As to the geometry issue, here too, your statement seems to be in an unnecessary contradictory vein and the argument even a bit “ ad absurdum” in logical terms. ( Please note that by “ argument ad absurdum” I don’t mean anything even remotely close to saying that your argument is absurd. It only means, in the precise language of logics, that one makes an extreme example in order to prove that his own opposite contention is true.)
In other words, who would ever think ( or has ever said) that letting off some DH will make the sail significantly fuller in the boom area, therefore more powerful, if the outhaul is set to the maximum ?( “ to the end of the boom”)? Of course not! I would never say it and nobody would! So there is nothing to contradict!
But I do appreciate your comments, because they contribute to dispel the confusion and to add to knowledge
Ittiandro |
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konajoe
Joined: 28 Feb 2010
Posts: 517
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| Posted: Sun Jan 25, 2015 1:29 pm Post subject: |
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Oops! Sorry for the misunderstanding. My floppy leach/planing comments were meant to be in response to this quote, not something you said.
| PeconicPuffin wrote: | | Note that if your intention is to plane, your sail must still have a floppy leach in order to plane in the lightest winds. The full pocket is great, but the wind still needs to be able to slip off the sail easily to develop lift. It's a common mistake to kill the floppy leach (your exhaust, if you will) in pursuit of power. . |
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konajoe
Joined: 28 Feb 2010
Posts: 517
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| Posted: Sun Jan 25, 2015 1:31 pm Post subject: Re: light wind rigging quandary |
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And my geometry comments were the result of this. Again, nothing you said.
| coachg wrote: | | Yes, this is because as you increase down haul the mast bends and effectively moves the leading edge of the mast farther away from the clew which flattens the sail similar to increasing out haul. As you decrease down haul the mast moves back, shortening the boom length & deepening the draft. |
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