Claudio
I agree, the more panels, the more effect each panel has and that will be part of the learning curve. I am going to have to decide on a testing method to return consistant results. Probably a tight outhaul and little or no twist would be the most reproduceable. The luff curve is another thing, I suppose for testing that no curve would be the way to go, I’ll have to think on that. The one thing that is nagging at me is the very top seam. If you want to have 10 or 12% draft at the top it has to be a fairly dramatic bend because it is the first seam(it hasn’t the influence of the other seams as the seams close to the middle of the sail). This is part of the verticle curve you mentioned.I will see as I ply with it.
Off to town for feeler guages
Don
Quote:
“PS: have you tried on the RG65 a single panel sails ? the outhaul adjust should be sufficient !”
Actually my sails are currently single paneled. Whilst this is OK with the jib, I think multipaneled could help with excesive twist in the top of the mainsail. My current main is 84 cm. tall, and with outhoul alone you cannot get any draft in the topmost of the sail. Granted, my rig setup probably is not the most effcient…
Anyways, I want to do a set of multipaneled sails for my JIF-2 (rg-65) mainly for two reasons:
a) as practice
b) my 1/20 Luna Rossa is at its extremely ealry stages (in other words, we are just planning this up, printing plans, drawing profiles, etc.).
To get 10-12% on the top panel, being very small, you may have interest to use a more flexible bar as a thinner plexyglass (~0.6cm as the adhesive width) . Try also to put more wedge thickness with several samples that shall be connected anyway with other panels to appreciate the bent. Blow some wind it may help to pull up your conclusions. You may come up with another Table that fit better your requirements. Be carefull passing from 0.35% to 0.40% make a big change in the seam.
Filler Gauges are perfect.
Actually the tool has non name: in Italy and France is called “Tool to make sail seams”. Any uggestion are welcomed
Claudio
Let’s try this name: ToMSS
Or just the short reverse " Sail’s tool" = SST
Claudio
Who invented it? Maybe name it after him. I think he deserves a little recognition.
Don
Agree
I discovered the Tool in the Italian site :http://www.nonsolovele.com
and presented by Paolo Saccenti, the Club A.MO.N. President.
Actually the famous 0.4% described it may come from a diffused knowledge of the art of old sail’s manufacturers. Recently, during the preparation of my reporting, I went to discuss with the engineers of Elvstrom and Northsails. Both were surprised to see the Tool and finally I quit them without a clue on the origins, they assumed to be an empyrical approach. I used the SailCut programme to detect the shape of the panels, was difficult but I managed. I got also some others sources and finally some 100 samples in order to make a statistic evaluation as probably did old manufacturers. Mathematicians did not help me either therefore I decided to go backward - from hardware to theory .
I was entusiastic the first time I saw it, therefore I decided to let others to discover it with some additional info like the graphic table. That’s all.
Claudio
Hi Claudio
That was not very helpful of them… (smile). The spreadsheet I developed recently (download from http://www.onemetre.net/Download/Sailblok/Sailblok.htm) can be used to calculate some of the parameters of your system.
Because you are using a “direct entry” of the draft into the seam, set the “bevel angle” to 30 degrees. This makes the bevel factor 1.0, ie unity, and leaves the rest of the draft, ie all of it, to be inserted by the curvature of your spline. I reproduce the spreadsheet details here, with bevel set to 30 degrees, block chord and panel girth set to 240 mm, and the wedges (that is, the block “height”) set to 0.9 mm.
Bevel angle b 30.00 degrees
0.52 radians
Block chord 240.0 mm
Block height 0.9 mm
Block draft 0.38 %
Block radius R 8000.5 mm
"Panels on block" characteristics
Girth s 240.000 mm
Subtended angle f 0.0300 radians
Chord in use c 239.991 mm
Height in use h 0.900 mm
Draft "in use" 0.37 %
"Seam sewn in" characteristics
Due to block curvature 0.007
Due to bevel 1.000
Change in girth 1.800 mm
Girth adjusted s' 241.800 mm
Height of seam h' 12.751 mm
Draft sewn in 5.31 %
You can see that 0.9 mm wedges over a 240 chord seems to introduce a curvature of 0.37% (the radius of the curve is 8000 mm!), but when this is sewn in, or glued in as you do, it turns into a 5.31% draft in the seam. If you play with the spreadsheet, and try a 0.4 mm wedge, for example, you will get around 3.5% draft “glued in”. To my unexpert thinking, this seems exactly right!
I have been thinking how to get a different curve into the seam, and not some simple variation upon a circular arc. As I seem to recall, architects and draftsmen used tapered splines to obtain fair curves on their plans, and think this would work well for your system. I’ll keep it for another project to try and figure out how the curve is affected by a taper (for example, if the thickness of the spline goes from 10 mm at one end to 8 mm at the other…)!
Hi Don
Dan might have corrected the Accumeasure results for camera angle and distance from center-plane. There is a spreadsheet which calculates these corrections, and some other stuff as well:
http://www.onemetre.net/Download/Sailmeas/Sailmeas.htm
Worth recording corrected values, since it is difficult, if you do not rigorously use a jig, to reproduce the same camera position, and hence you can think you have variability in your work when it is only variability in camera angle…
Hi Lester
thank you for your explanation I will try to digest what you says.
Actually my pratical experience shows “draft %” that are 100% bigger.
I wonder if a factor of 2 is missing somewhere . Do You refers to one or two wedges ?
My sail, as said before, with a 0.4% resulted above 11-12 % draft when fully assembled and not 5.31% as you may claim.
A.MO.N. in Milan obtained similar results suggesting the 0.4% for 10% draft and 0.3% for a draft of 5-6%.
If I do not go wrong, Don used my graphic table and obtained what he was expecting . Where is the bug ?
With my respect
Claudio
I just did last night a 3 panel jib. I must have done something very wrong as it came out flat… I think I did something different with the first test I did, that was setting the first DS tape after inserting the wedges… Will dissasemble the sails and try that aproach to se if I get any difference.
Besides, the jib I did is fairly small (each panel had a chord of 140 mm and 79 mm each) so draft could be hardly noticeable.
I was wondering about the formula, I’m not very good at geometry, but out of curiosity, why divide the chord by 100?
Hi Claudio
Perhaps a sail with 5% draft “sewn in” actually flies with around 11-12% draft? The page on the effect of the outhaul (http://www.onemetre.net/Technicl/Outhaul/Outhaul.htm) suggests that a sewn-in draft of, say, 5%, could easily become 12% when flying because of twist, leech tension/kicking strap/vang, outhaul, mast bend, and wind pressure/gravity. The sail I studied had 0% sewn-in draft, but the middle of the sail showed 9% draft because of these other factors… It is extremely difficult to measure the “actual” draft of a sail when it is lying on a table or even when it is suspended from a hook, so when someone reports “My sail draft is 10%”, it is very difficult to know what was sewn-in, what was due to gravity, what was due to the outhaul, and so on.
Do You refers to one or two wedges?
A wedge of 0.9 mm on each side of the spline makes a “hump” of 0.9 mm in the middle. It is this “hump” that the spreadsheet requires, and is equal in size to the size of each wedge. If one wedge was 0.5 mm and the other was 1.0 mm, then the “hump” would be 0.75 mm.
Lester,
quote : “It is extremely difficult to measure the “actual” draft of a sail when it is lying on a table or even when it is suspended from a hook”
Therefore one can shows the “draft” he like to see !
Actually I wonder about the Acumesure utility since everything can be modified as we want and let believe anything.
Villeret in France, in two different occasions, presented a sort of Ruler to cut the panels edges . In one suggest a curve of 0.57% and in the other 0.42%. No indication are given on eventual final draft of the sail except on one where 4 to 7 % draft is indicated. Taking this for valid, then : 240 mm cord X 0.57% = 1.36 mm wedge thickness and not 0.9 mm as you suggest.
In France is often mentioned the 4/1000 to be applied to a cord to obtain a draft “x” not better identified.
I miss something somewhere, you may be right but the all affair is very vague.
Fortunately with my tool I can work and make all curves I want and use as a “relative” approach without the need of several expensive blocs.
Have a good day
Claudio
Marino,
I’m surprised !
[QUOTE=I was wondering about the formula, I’m not very good at geometry, but out of curiosity, why divide the chord by 100?[/QUOTE]
Simply by the formula . i.e. for 8 % draft to a cord of 165 mm
according to the table you will have : for 8% draft you have 0.255% Fm
therefore
165 x 0.255 % = 165/100 x 0255 = 0.42 mm this is the thickness for both wedges.
Claudio
I asked before, and ask again: Maybe this method is not efficient for really short chords… could it be?
Yes, but in the formula, where does the division by 100 comes from? I do know how to follow a formula, what I’m trying to understand is why divide the chord by 100 and not, say by 10,000 or 2??
Marino
I’m sorry if you prefers call it 2.55/1000 just for fun !!
These percentages (Fm% in the table) come from experimental and repetitive manual work done to manufactue the sails since ages. Everything appears to be empiric but works, likewise for the wooden barrels tu put wine into. If you have a better explanation …
Claudio
Go to page 8 and observe the photo of 100 mm wide panels showing a draft. If you din’t succeded probably you made it wrong. Read all the posts including the ones of Don and you will see.
Claudio
Claudio, don’t take me wrong… I just wanted to better understand this method, which, as I have stated before, seems to be the most practical for my purposes. Is not a matter of how I prefer to use it.
For me, as I don’t participate in any high level event, is not critical wether this method gives you a draft accurate to 99.99999999% or not…
But I’m curious about the rationale of the formulae, just in case any of the more experienced guys in this forum, could make it even better…
Thanks again for sharing this with us, and let’s see if together we can make it even better!!!