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light wind rigging quandary
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Sailboarder



Joined: 10 Apr 2011
Posts: 656

PostPosted: Fri Jan 30, 2015 11:25 pm    Post subject: Reply with quote

konajoe wrote:
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.


I see what you mean, and I think you don't have the same definition of outhaul as is commonly accepted. O cm outhaul is neutral, no extra tension on the clew. 1 cm of outhaul requires extra tension to move the clew out by 1 cm. If you are initially adjusted with 0 outhaul, and if you increase downhaul, the clew position will change, and you will need to reajust your outhaul lines just to get rid of the slack in the lines, otherwise you now have -1 OH.

This is not an increase in outhaul: it's just putting it back to where it was. There is no increase in tension trying to flatten the sail belly that way.

However, the distance between the clew and mast increased while increasing DH, and this is obviously linked to safe sex, oups I meant to a flatter sail.
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coachg



Joined: 10 Sep 2000
Posts: 3546

PostPosted: Sat Jan 31, 2015 2:02 am    Post subject: Reply with quote

Sailboarder,

The way I learned to rig, and obviously there are other methods, was that neutral OH was when you pulled on the OH until the leach between the batten just above the clew and the clew was level so that there is tension in the OH for neutral. To get negative OH you then release the OH so the batten above the clew starts to drop below the clew. For positive OH you just pull extra after reaching neutral. Based on the mast you use, how high or low you set your boom, and the amount of DH you put on the sail, neutral could be many different locations with the same sail in boom settings.

Coachg
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Sailboarder



Joined: 10 Apr 2011
Posts: 656

PostPosted: Sat Jan 31, 2015 7:32 am    Post subject: Reply with quote

Coachg,

Interesting, and similar to what I learned. In my case, you pull the clew with the fingers until you hit some real resistance. That would be neutral. For many people, a boom set to negative outhaul will push the clew towards the mast when laying on the beach.

The key here anyway is that neutral changes position depending on mast, DH setting, etc...
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techno900



Joined: 28 Mar 2001
Posts: 4161

PostPosted: Sat Jan 31, 2015 9:29 am    Post subject: Reply with quote

Sails rig differently, so defining what neutral outhaul is up for debate. Most smaller sail (non-cam) require some force to pull on the outhaul to get it to what might be considered neutral, and what could be called the "ideal tuning point" (there is probably a better description than this).

My dialogue/posts have been regarding multi-cam race sails. For about 12 years, at least with Gaastra and Maui Sails, there is NO tension designed into the outhaul line when properly rigged, or what I call neutral. When powered, tension is naturally added to the outhaul, but the shape of the sail changes very little, except for twist in the upper leach. You can sail these sails with no OH line attached with good efficiency in light winds.

As mentioned before, If I am to go for maximum pointing, I will tighten the OH a few cm's for a flatter profile. To run deep, I slack the OH a few cm's from neutral for a fuller profile. The fuller profile adds SIGNIFICANT stability to the sail on deep, well powered downwind runs.


Last edited by techno900 on Sat Jan 31, 2015 11:21 am; edited 1 time in total
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isobars



Joined: 12 Dec 1999
Posts: 20935

PostPosted: Sat Jan 31, 2015 9:59 am    Post subject: Reply with quote

I've rigged hundreds of sail brands and models, from race sails only a big weightlifter could DH according to Neil Pryde specs to a HOT sail that required a DH tool to OH it properly to a slalom sail THROUGH which the back end of the boom passed, and from 0 to 7 cambers even in sails below 6.5m. We rigged them according to the mfrs' specs, often with the sail designer at our elbow. Neutral was always defined by DHing properly*, then pinching the sail's clew between thumb and forefinger and pulling gently until a sudden increase in resistance indicated neutral ... the fairly abrupt point at which the OH tension suddenly increased from zip to obvious.

*THAT'S where manufacturers differed, and dramatically. Some defined proper DH by the relationship between mast and battens, some by the shape of the foot batten, one brand and model by how many big deep vertical folds there were in the luff panel just behind and parallel to the mast.

But since a sail designer designs his sail to perform optimally throughout defined tuning and wind ranges, tuning and operating outside those ranges is likely to result in unintended -- i.e., worse -- handling. It thus makes much more sense to buy the right sail (and mast) designed for one's special needs and use it as intended, rather than buying a sail designed for some other purpose and forcing it to operate suboptimally in a different regime. Nobody buys a Corvette to haul (or attract) anything but ass (and cops), and nobody buys a motor home to race the canyons above LA.
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konajoe



Joined: 28 Feb 2010
Posts: 517

PostPosted: Sat Jan 31, 2015 11:14 am    Post subject: Reply with quote

First, can someone address ittiandro's last post? I think he may have misinterpreted some stuff.

OK. So let's figure out what is really making the sail flatter or fuller in the boom area. In the 'sex causes lung cancer' case, we would see what happens if we didn't smoke after sex. For us, we'd want to change the outhaul without changing the downhaul.

Start from medium recommended downhaul and 1 cm positive outhaul. Next, downhaul the sail to max. Extend the booms so that you can go back to 1 cm of positive outhaul, and note how much outhaul line you had to pull. This is your base case. Sail with it, powered up, and note the fullness of the sail in the boom area.

Starting from the same point (medium downhaul and 1 cm positive outhaul), leave the downhaul tension constant. Now, extend your booms, and pull the same amount of outhaul line as you did in the base case. Sail with it, powered up, and note the fullness of the sail in the boom area.

What did you see as far as fullness in the boom area? Hint: Sex does NOT cause lung cancer.

You're working with the same amount of material between the mast and clew, guys. This can be modeled with a piece of graph paper, a piece of string, and three pins. Fix 2 points on the string with 2 of the pins, but do it in a way that the string is not tight. Use the third pin to set where the max draft is. Pull that third pin just enough that you have 2 straight lines. On the graph paper, mark the maximum draft. Now, keep those pins attached to the same points on the string, and move those 2 pins farther apart. This represents adding more outhaul. What happens?

We all know what happens. Because, at the limit, when the string is pulled tight, there will be no draft.
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techno900



Joined: 28 Mar 2001
Posts: 4161

PostPosted: Sat Jan 31, 2015 11:14 am    Post subject: Reply with quote

iso said:
Quote:
Nobody buys a Corvette to haul (or attract) anything but ass (and cops), and nobody buys a motor home to race the canyons above LA.


In the late 60's, I had a '65 XKE coupe that pulled a small trailer with my Husky 360 motocross bike aboard (plus two other bikes at times - Montessa 250 Capra and a Rickman Hodaka 100). An unlikely pair (XKE and trailer). The hitch guys did a good job of customizing what was needed to work around the exhaust pipes.
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konajoe



Joined: 28 Feb 2010
Posts: 517

PostPosted: Sat Jan 31, 2015 11:45 am    Post subject: Reply with quote

Techno, you'd make a great politician! I'd vote for you in a second.
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techno900



Joined: 28 Mar 2001
Posts: 4161

PostPosted: Sat Jan 31, 2015 11:50 am    Post subject: Reply with quote

Another way to explain it to ittiandro is to look at aircraft wings.

Low speed aircraft typically have thicker wings (deeper foils) for greater lift at slower speeds (light wind). As aircraft are designed to go faster (fighter jets), the wings are skinner (profile) because as the wind rushes by, less lift is needed so the foil/draft is really shallow.

The other reason that higher speeds/wind require smaller foils is to minimize drag. The profile of a 10.0 sail with a deep draft simply will not go very fast because of the drag on the foil/sail. When you look at the draft on a 4.0 sail, it's your fighter jet, with little foil because it will be moving much faster than the 10.0. Faster means a combination of wind speed and board speed (air speed over the foil).

So a deeper foil will offer more lift/power than a shallower foil. As konajoe pointed out with his string example, more outhaul will flatten the sail and reduce power. I guess the debate is the effect of DH, but that may be sail dependent. On my sails, more DH flattens them, as seen by the new slack in the OH line. We are taking a finite amount of material and spreading it over a larger area, so the draft has to get smaller/shallower (same with added OH).

Too much screwing around adjusting OH and DH will likely have a negative effect. Rig to specs on the right mast and don't add or subtract more than 2 cm on either DH or OH and you should be good to go.

If you don't have the specs or don't have the right mast, then your only hope is to have an experienced windsurfer take a look. Of course, take this with a grain of salt since there are "experienced" windsurfers that have never rigged a sail properly. The other option is to go on line for help and then get buried in needless, confusing detail. Welcome aboard.
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coachg



Joined: 10 Sep 2000
Posts: 3546

PostPosted: Sat Jan 31, 2015 12:11 pm    Post subject: Reply with quote

Techno, neutral is just a starting point, not the ideal rigging location for a sail. It is just a frame of reference to get everyone on the same page, especially when teaching a large class of 12 students.

Iso’s, the reason I was taught to visually look for a rise in the leach was that everybody’s “feel” is different. The Hulk will require significantly more resistance than I to feel the OH. My wife’s feel, being a dental hygienist, is far more sensitive than mine. Again, the goal was to get everyone’s neutral as close as possible vs. the feel method. From this neutral, you then rig for feel. My quiver is Naish & Mauisails so from years of sailing them I have found that Naish prefer positive outhaul while MS prefer negative based on the method I use.

Coachg
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