According to my spreadsheet, wedges of 1.00 mm on a chord of 100 mm will give a draft of around 8.7%. Using Claudio’s “Graphic B”, a wedge of 0.5 mm will give a draft of around 15%.
I did not tried yet, but I recall the photos at page 8 where I tested on 100mm cord with Fm of 0.35% and obtained almost 10% draft in the middle seam.
Claudio
Hi all
One of the difficulties we have here when trying to exchange useful information is that our “measurement laboratories” are rather different from each other. If we are going to be able to meaningfully compare my sail draft with your sail draft, we have to agree on the measuring arrangements, otherwise we will simply be comparing oranges with apples.
We know that sail draft depends upon a number of factors: outhaul, gravity/wind pressure, leech tension/twist/kicking strap, mast bend, and so on. I’d like to suggest that we report our findings according to this “standard condition”:
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sail outline/profile is cut to shape (that is, it is a triangle or similar, not a rectangle).
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sail is suspended horizontally on a jig or similar at its normal three points of attachment at tack, clew, and head (that is, the sail is not attached to a mast), and the body of the sail does not rest on any surface.
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there is sufficient tension in the luff of the sail so it sags by only 10 mm between head and tack.
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outhaul (clew) is set to give 5% draft in the foot of the sail.
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clew is adjusted so that the sail is twisted and there is very little tension in the leech. The amount of twist should be set at 15 degrees – that is, the top seam or batten should twist off by 15 degrees relative to the foot of the sail.
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a digital photo is taken from the head of the sail, looking down to the foot, so that all the seams of interest are in shot, as well as the foot of the sail.
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the camera lens should be 300 mm away from the top seam, and should be in a plane about 200 mm above the nominal plane of the sail. (If different distances are involved, no problem, these are reported so that appropriate adjustment for camera angle can be made.)
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we report the statistics of the sail – distances between seams, thickness or weight of the sail material, lengths of the seams, sizes of the wedges or whatever used during broadseaming.
This would then allow us to make great progress in figuring out what is going on!
Lester,
I perfectly agree and I will start working accordingly .
Claudio
Lester -
without having to go into a lot of detail, for those of us with either “fathead” or more rectangular sails … what differences would you expect to see, if all other parameters except profile shape remain as per your suggestion?
Because we are (perhaps) attaching the head of the sail further out towards the leech, or because we may not have the extreme roach as some pin-head sails, or more batten support higher up to retain a flatter sail - how would this impact a “standard”?
I am just curious and won’t interfere with your experiments - but am wondering if sails would expect to be seen flatter - or fuller - or what would I notice that might really be different?
Hi Dick
The idea is to have a “standard measurement protocol” when we are collectively exploring sail draft. So I’m suggesting that the sails we examine and measure have their intended profile before we start measuring, and I’m suggesting that we only deal with “three-point attachment” sails in the first place. So it shouldn’t matter if they are fat-head or full-roach (but see below).
Because we may have more batten support higher up …
Ah. I would expect the “standard measurement protocol” to measure the sails without battens, certainly without any that affect the drape of the sail in the measurement jig. The idea is, I guess, we are trying to find out what the effects of various broadseaming techniques and approaches have on sail shape, and this would get too difficult if to start with we looked at battened sails… Maybe later on, when we have basic data, we can then look more widely, and then we’d be able to make informed judgements about the effect of roach, fat head, battens, etc on sail shape.
Hi Dick,
Flat or Full, but how to make it this is the question?
The discussion essentially is centered on the method to be used to provide the shape we want.
Various tools are actually used, the most popular are : the “Blocs”, the “Rules”, the “Moulds”.
All these tools requires the manual intervention (fingers) to introduce the sail schapes, and therefore the manual intervention means, by definition, “human errors”. Further, differents shapes need differents tools to produce a flat or full sail.
The tool I have introduced is a new method that has, in my opinion, some avantages : is small, no "fingers"are neded to make the shape (semi-automatic) and one tool only is needed.
Reducing the manual interventions the “reproducibility” is easier to achieve.
We have to trust the tooling we use and therefore a “calibration curve” is required. The calibration being the standard of that tool. In order to compare two tools we need a common base as such that the measurements be comparables.
Once the tool is “calibrated” then is up to user to decide if he want to make a flat or a full sail being "sure "
that this will happen .
Actually I will prepare, as Lester suggested, a "bench tool " that will help the measurements with the method that the "Status of the art " is offering. This is my proposition.
Claudio
Hi Claudio
Looks good! My guess is that the clew adjustment will need two orthogonal components, illustrated here, one for outhaul, and one for twist/leech tension.
Yes I forgotten to draw it
Claudio
Humble suggestion is to leave sail testing to Don and Claudio, as they have shown the skills required to develop any jig needed and to perform testing on a more controlled way. I would love to be more involved, but, lack the skills required to do tests in a controllable, repeatable way.
Marino
You made your sail.That implies certain skills. But you do need a flat surface a little bigger than your sail that can drilled and screwed, ie. not a dining room table!
Don
Lester
Do you have any specific tests you would like done? Are we going to limit ourselves to 3 or 4 seams. Can I suggest uneven panel lengths(shorter towards the top) so that we can re-use panels from one test to the next?
re Claudio’s box
What is the vertical measurement from the camera to the sail surface,200 mm? Where do we measure to on the camera? The lens? The middle of the body? Does using telephoto affect the data?
Don
Thanks Lester & Claudio -
I understood that you wanted to limit the basics to develop a controlled basis for further study - but was wondering if either of you have any feeling (or guess) what might happen if profile varied toward rectangular. Was looking more for a “guess” - not an formal photo based study. If not, I certainly am content to wait.
We had a “pub” discussion (actually over coffee here at work) about panelled versus non-panelled sails. We all know and agreed that a panel type sail offers better shape - but the question unanswered is what is difference with a single panel sail often provided in a kit? If someone wanted really flat sails in general - would they be better off to simply use a flat single panel, or would there be advantage to try to sew in a series of seams to make a “flat” sail? Question arose from the multihull interests here since we generally find most monohulls sails much too full for our lightweight and higher speed boats. We don’t need the power from full sails as often as we need fast sails.
If not too much trouble, could someone please include sails from perhaps a Victor 1 Meter Soling - or similar large but non-panelled sail - strictly for a base comparison? I have a single panel Victor 1 Meter main and jib I would be willing to send to someone for analysis and for a baseline of exactly how much shape really resides in a single panel sail. If someone were willing to do a photo analysis, please let me know and I will get a sail set off to you.
Thanks.
Dick
Set it up roughly according to the above and post the picture here. You could use black tape to put stripes on it. You could also download Accumeasure and do it yourself. It is very easy to use.
Don
Point made 
will try to arrange something with some scrap plywood… However, and I think this is good, my sails will be mainly for the RG-65 class, high aspect if you noticed… and a lot smaller than those of US1M and IOM…
Marino,
bravo ! but you forgot the Master of many as Lester
Ciao
Claudio
Hi Don
The tests are up to you, I think, in terms of what seems interesting. Speaking personally, I’d love to hear about results from systematic analyses where there was use of different: wedge thicknesses, positions of max draft, weights of sail material, panel lengths, whatever. It would be interesting to hear about the effects of systematic changes to outhaul, twist, or downhaul tension; to know if the results were reproducible when the sail was turned over, when the sail was set on a warm day and then on a cold day, and so on…
Where do we measure to on the camera? The lens? The middle of the body? Does using telephoto affect the data?
Ideally, measure from the film plane – pretty much the back of the camera. Telephoto doesn’t matter for measurement purposes.
Hi Don
Ah, could I respectfully suggest the use of tape be avoided? It does distort the sail appreciably!
Hi Dick
The issue with a panelled sail vs a single-panel sail isn’t, I think, whether one is flat and the other has draft sewn in. The only real reason to broadseam is to control the vertical distribution of draft; the only reason to use a single panel sail is if you don’t care about your vertical distribution. Controlling your vertical distribution of draft is mainly intended to accomodate the wind gradient, both in terms of wind speed and apparent wind angle, and secondarily to accomodate the lift coefficient regime you sail in and hence the amount of tip vortex you generate.
I have noticed, no matter what method I use, that the sail seems to favor the position in which it was formed. If you turn it over(other tack) the shape doesn’t seem as nice. Anybody else see this? Any way to avoid it?
Don
I’ve seen the same.Was thinking to alternate the sides while assembling the panels, but I later though it could case the sail to assume a really odd shape. Does the same happens with blocks? I think so. Will it go away after a couple of sailing sessions?