All:
We need to revive this thread. I’ve completed the first two panels of a radial cut jib for the Luna Rossa. I’ll try to post pictures tonight.
I’ll be checking Lester’s spreadsheet to try with it’s values. I’m thinking about pursuing the following drafts (top to bottom): 12, 14 and 12, with a 45 % location of maximun draft (from luff to leech)… are they OK for low winds and a jib?
I made a US1M main with three seams starting halfway up. I used multiplication factors (MF) of .7, .8 and .9 from bottom to top. I ended up with drafts of something like 10,12 and 10 with the foot set at 5% and twist at 16 degrees.(Lester, it is a real pain in the butt to get the sail set at those parameters.) I was trying to get a big draft in the top seam to encourage the shape to go right to the top. It worked to a point. Depending on the thickness of the material the draft might be reluctant to pop-through when tacking. Also with that much draft at the top the sail twists off til a bit above mid-sail and then twists back.(There is more twist in the middle than the top) This might be diminished with lighter cloth, I don’t know. The sail looks like a shape I’ve wanted to try so I will finish and test it.
Hi Don
Yes, because the sail isn’t a “finished” triangular shape, it will not hang happily and I would guess that getting it to twist off would be close to impossible…!
That is a finished sail, ready to go on the boat. US1M have a 2 1/2" roach and with the camera at the top it just looks rectangular. What was the pain was the set-up. I would set the draft and twist to what I thought was right,take a picture, run it through Accumeasure, find it wasn’t even close to 5 and 16, back to the shop,readjust,do it again. it took four tries to get it this close.
Don
Hi Don
You’re right, it does look rectangular! My mistake.
I would set the draft and twist to what I thought was right,take a picture, run it through Accumeasure, find it wasn’t even close to 5 and 16, back to the shop,readjust,do it again. it took four tries to get it this close.
OK. What were the sail measurement when you set it up to look right in the first place? If a “right-looking” US1M sail has, say, 10% draft and 6 degrees twist, then it might be better to standardise on these numbers instead…
These are the numbers I get from Accumeasure for your photo. I guessed at the heights of your stripes…
Lester
I’m actually quite pleased with those numbers even though there is probably too much draft. What I like is that the draft is quite even from top to bottom. I have some questions about your numbers. Does the spreadsheet not care if you are looking from top or bottom? I see you put in 1600mm deck to lens. I have been putting in “0” deck to lens and then measureing from “lens” (or directly below it) to the stripes for the “deck to stripe”. I figured that since I didn’t have a deck I would just assume that the camera was on the deck. I also assumed that the spreadsheet wouldn’t know if the sail was upside down or not. Do I pass? What do you think about the twist starting to untwist at the top? I’m hoping that wind pressure will fix that.
Don
Hi Don
Yup! But hey, the point of all of this is that you now know what you’ve sewn in and you can take your performance comparisons from there…
What I like is that the draft is quite even from top to bottom.
Well, it might be even but I’m not sure it should be so given the 5% draft set at the foot. While middle to top might be around 11% (if that is what you want) I’d expect to see around 7% or 9% at the lowest stripes.
Does the spreadsheet not care if you are looking from top or bottom?
It doesn’t care; all it wants is that everything is measured consistently from whatever place you choose to call the deck.
I see you put in 1600mm deck to lens. I have been putting in “0” deck to lens and then measureing from “lens” (or directly below it) to the stripes for the “deck to stripe”. I figured that since I didn’t have a deck I would just assume that the camera was on the deck.
Well, the camera is at the top of the mast! You can decide where the “deck” is, maybe at the boom, but then everything should measure properly from whatever that point is.
What do you think about the twist starting to untwist at the top? I’m hoping that wind pressure will fix that.
Twist should be even from bottom to top, so the “untwisting” at the head is a little worrying. I assume that it is due to the deep draft you’ve sewn in and the fact that the fat roach is tensioning the leech. I wouldn’t want to rely on wind pressure, because when the wind gets up you’ll need really serious twist to keep the boat on her feet.
I think I’m running into a “Catch 22”. In “The Art and Science of Sails” he suggests that the draft should increase as you go up the sail, but if this is going to cause this “untwisting”----. Maybe it’s just that I went to the extreme to see what would happen and saner numbers might correct it. I guess I should sail it first and then a re-cut. One of the problems with using the 3 mil mylar is that it doesn’t flow with the wind and show when it’s luffing or stalling. I wonder if the more twist you mentioned( I’m thinking as I’m typing, it’s a good thing I type slow) would get rid of the uneven twist. That I can try in the shop.
Don
Higuys,
I’ve been reading along since I put my boat up for the winter. So I’d like to try my luck at some sailmaking.
Is there a BIG diagram of the sailblock I can get so I can make my own block? The only one I found isn’t very detailed, so I don’t think the shape would be that correct.
Tom
Go back to page 6 of this thread and start reading there. We have been experimenting with Claudio’s gadget. It may not work any better than blocks but it’s way easier to build.
Don
Hi every body,
I was absent for a while (chirurgical operation) but I’m back and have to apoligise for the graphs presented.
There a strange mistake somewhere, in fact having reviewed the story, actually the Wedge thickness to be used is much closer to the Gilbert graphic . Possibly this is due to the fact that both panels edges need to be cut at the same way. My tool allows only the curve of one panel while the other remain with the straight border. To compensate, it is therefore necessary to put the total curvature on one panel only, I guess !!! Why I missed , I do not knows yet … Still I need to recover my head !!!
Sorry
Claudio
At least the discrepancy is discovered. For most of us it won’t really matter because we will build a sail, try it and then modify it to try and make it better. Eventually we would have discovered what mltuplier produced what draft for our particular sail. Your block makes reproducing a sail straight forward and as long as we keep track of the multiplier used( I’ve been writing it on the seam) you can figure out what to change. The only time we need to know the % draft is when we are telling someone else. The number of seams, the distance between the seams and lord knows what else will effect the draft that a given multiplier will produce and though it would be nice to decide on the amount of draft we wanted and build it first try, I don’t think that will happen. It’s been dead calm and foggy here so I haven’t had a chance to try my new main. I would like to carry this thread on into other areas of sailmaking. Cutting luff curves, luff treatment(wire,string and so on) grommets, eyes, re-inforcement patches. That kind of stuff. I hope you are recovering well from your surgery.
Don
Claudio: Hope you continue to get better.
Don: I like your idea.
All: I broke my tool!!! (insert crying noises here)… Looking for a more suitable piece of wood now…
Very kind of you,
“they” cleaned up all my sinus, one full week in hospital, recovery is slow.
I was experimenting with various curves and tissus in order to understand the 100% gap difference noted with the Gilbert graph in the Fm. Much depend on the tissus weight to but also on the flexibility of the ruler. I tried soft plastics, wooden and alluminium as the original tool. I tried also to put only one wedge of double thickness on one side only and positionning the panel at 40% of cord. I used the Accumeasure and the frame presented here and shot some photos.
I demostrated that any results can be achieved with the same sail and all depends on how much and others can pull or relax the tensions. After all, this is what really matters. Once fixed the acceptable sail shape the FM will be fixed anyhow as fonction of tissus.
At the end of story it will remain only One Tool and possibly a couple of adjacent curves on a paper that each one will find satisfactory for himself. I’m not satisfied having indicated wrong data and therefore
I will continue to search for the famous 4/1000 applied on the initial projet, beacause this in not yet clear to me.
Ciao to everybody
Claudio
Don and others,
this may be of any interest ?
Mast effects on sails.
according to my readings, (close-hauled) a mast diameter of 10% or more of the chord produces a loss of sail’s lift in the order of 30%. It is also exstimated that the loss of efficiency of a main, can varies from 10% at the foot up to 85% at the head due to the mast drag induced.
Since is part of Making Sail tecnique, is anyone interested to develops a discussion on the subject ? Any ideas ?
Claudio
I believe that sleeve sails(I think that’s what they’re called) are not legal in most classes. Maybe the multi-hull or land yacht guys?
Don
Hi Claudio
There are two major problems with double-luff sails of the sort you illustrate.
One is the difficulty of broadseaming some shape into the luff. Turns out almost all of the double-luff sails I’ve seen are single-panel (one piece) sails because of the near-impossibility of shaping the double luff.
Two is the difficulty with mast bend. Even using stiff carbon fibre, it is common to want to control mast bend via backstay tension in order to push a little draft into the mid-sail in lighter winds, or pull draft out of the head in heavier winds. But the double luff makes anything other than a perfectly straight mast more or less impossible as well…
Having said that, many vane “A class” boats (and some older radio boats) have double luff, single panel jibs with carbon rods as jibstays. Advantage is not having jibstay sag when the wind gets up…
So far, what I knows, is that in a the Class M the sail surface shall include in this case also the mast .
Claudio
An exemple of sleeve.
The sleeve do not need to be a full tube from foot to head but it can be segmented.
Assuming that the mast induce a reduction of efficiency in the order of 30 % as Croseck demostrated in the wind tunnel, see previous post, assuming a sleeve coverage of 50% of mast lenght, one could in theory deduct that the mast drag will be also reduced of the same amount. Even 10% will be great !! Windsurf , 49’er, etc already use this type of sail with a pre-bent mast.
Actually I do not want to talk yet about full profile sails, but … !!
Your comments ?
Claudio
Regarding the TYVEK material… How well do you think it will take the double-sided tape? Also, what would you do to put a scale-like pattern to it- I was thinking about making a set for a smal 12M boat, whiuch comes with cloth sails that have kevlar-looking print on it like the big 12M sails do.
If the works, I might try a set for a 1m boat with scale looks.
thx