Hi Marino
good work probably adapted for strong wind. It is not clear how the foot look like. I suggest to visit this site.
http://www.wb-sails.fi/news/98_11_PerfectShape/Main.htm#Perfect
you have 3 buttons to press - observe how the depth is moving.
Claudio
Marino
Yes and I guess it also helps describe the shape when a person gets that far into it. I just woke up so I haven’t run your sails yet, I want to see if I get the same numbers. If you haven’t already you should build a jig that holds the camera in the same position every time. Consistancy is tough without one. I’m think you should include the bottom of the sail so you can measure it and that way allow for the outhaul setting. Did you go to Lester’s site and get the download that compensates for camera angle? It make quite a difference, especially on the seam closest to the camera. Oh, the sails look good!
http://www.onemetre.net/Download/Sailblok/SailBlok.xls
Claudio
The boats are nice. How does the one with just the big jib work? I’ve had that idea bouncing around in my head for a while. I thought it was my idea! I guess it’s tough to come up with an idea that hasn’t been done before. How long do the florist film sails last? I’ve got some film but it seemed a little stretchy so I haven’t tried it yet.
Don
The idea was suggested by reading an italian yacht design book that was relating on various type of rigs. The CDCAT is based upon a boat developped already in 1922 by Montgomery in the Maine. Later reported by Ph. Bolger and revisited in 1984 under the name CS24
Booth having great performances but requiring also very skilled control. My CDCAT is faster than the Studio. The basic idea was to get read off the mast. The sail is acting as a plane wing that is working with relatively small incidence angles. If not carefull controlled it is easy to go in stall. I’m thinking to search for a plane sail, but …
Claudio
Very fragile it last very short time and not visible when is far away. Nice to see that’s all.
Claudio
They are well suited for low winds. They are very delicate to handle, specially when cutting. Using large reinforcement really helps in the corners. Like Claudio said, impossible to see at a distance, so grab your permanent marker and get creative!
I have enjoyed reading this thread, and particularly liked Claudio’s “gadget”.
I was unable to post until recently.
You will find that the luff curve built into the mainsail has an influence on the camber - depending on the amount of mast bend. This will make it difficult to check Claudio’s table of wedge thickness vs sail depth with actual measurements.
How much luff curve to build into the sail (to match mast stiffness/flex) is a completely seperate problem from how much seam shape.
Jon
Jon
If you have any little bits of information or help on figureing and methods of cutting luff curves please join in on the “Luff Curve” thread. I’m sure there are some great ideas just wailing to be shared.
Thanks
Don
Include as well as meny ideas on how does the luff curve affect draft… I’m in need of oggd shaped sails for low winds conditions… Any guidelines on how much draft should I’ll be looking for?
this post is removed due to errors in the graphics
Claudio
Claudio
I think you are right about different material thick affecting the graph.I also think that seam length should be considered some how, especially with thicker material. Some thing I know for sure is that plexiglass has a memory and that after a few short seams it will stay bent. It is neccessary to clamp it straight as close to the end of the seam as possible. I discovered this by accident when, after pulling the wedges, I had to pick up the block for some reason or other. I grabbed it across the block and noticed that the warp increased significantly. I then clamped it on both sides of the seam and got a better draft. I am know going to reverse the bar every now and then and I also clamp it close to the end of the seam. Maybe your aluminum bar is a better idea. I tied 1/4"x1" aluminum but it was too stiff for short seams.
Don
Don,
plexiglass has much lower memory than metal. You have noticed on my photos that I used clamps not for nothing ! It is written also in the "Instructions for use " at point 5. Honestly I do not have much trials with short cords (<100 mm) and heavy material, probably you may bring some new experimental hints.
What I knows is that for my Class M, the top panel seam is 105mm on the main and 125 on the jib.
Smaller dimensions may requires small jig ? I can answer on that.
All 4 seams are positioned in the upper half of the sail following the criteria suggested by Larry Robinson in his book, the outhaul being used for the rest of adjustments.
This is my aluminiumbar
Claudio
Hi Claudio
I’d expect the trend line to be curved rather than straight:
Lester:
Is that a suggestion or calculated data? This looks interesting…
I’m also in agreement with the notion of some compensation (or maybe a diferent table altogether) for chords smaller than 100mm, but I lack the experience to even try to calculate it.
Lester,
in theory you may be right but even in your courb the draft from 4.5% up to 8% it look like a straight line.
Further having adopted on my tool a multiplier factor of 0.45 and 0.5 %, I came up with a 50? polyester film main sail with a draft of about 12.5/13 % wich is 100% bigger of your suggested curve. With that curve applied to my tool, Don would have got a flat sail.
It will be nice if you could make this tool and possibly verify it practically? Otherwise, where is the bug ?
Claudio
It might look like a straight line, but it’s grow is exponential, rather than direct.
It is calculated from my spreadsheet.
http://www.onemetre.net/Download/Sailblok/Sailblok.htm
(Set bevel angle to 30 degrees, set your desired value of, say, 100 mm chord in both “block chord” and “girth”, and the thickness of the wedge as the block height. Out pops the predicted sewn-in draft. You can work the spreadsheet “backwards” by either trying various wedge thicknesses until you get the draft you are interested in. Or you can use the “Goal Seek” function of Excel by telling it the cell to vary, ie the wedge thickness, in order for some other cell, ie the draft, to equal a value you’d like to see.)
Hi Claudio
I guess your expression reflects the fact that English is not your first language. I’m afraid there is nothing “theoretical” about me being right, it is the simple laws of physics which deal with the way the draft is sewn into a seam by “pushing” in a little extra sail material. The function is a quadratic, and the resulting graph is a parabolic arc.
Further having adopted on my tool a multiplier factor of 0.45 and 0.5 %, I came up with a 50? polyester film main sail with a draft of about 12.5/13%
Do you happen to have a sail photo I could analyse?
… wich is 100% bigger of your suggested curve. where is the bug ?
That is what we are trying to find out!
It will be nice if you could make this tool and possibly verify it practically?
It would be nice indeed! But I am too aware of my limitations, having ten thumbs and no practical skills at all!
So that table is indeed for a given chord? If so, that kind of makes sense (scary), as for a draft of 10% the wedges must around 1mm… Is that right?
You have to be careful here. I agree that 1mm would make about a 10% draft but if you put two or three of them in one sail you may be up around 15%(wild-ass guess there). Lester is working on something that may be able to predict one seams effect on the next one(s). That may explain everything. I think all this head-scratching may be the reason that the big sail companies went to moulded sails(Joke) The funny thing about all this is that we may eventually understand all the interactions of one thing one the other and be able to build a sail the duplicates our designs and yet still make lousy sails. It’s trying to understand what the wind wants, thats where the answer is. Still if anyone figures that out we may be able to build it.
Don
I do suspect something.
My tool produce a flat curve only.
It seems to me that the blocs instead produces two “curves”, one representig the profile of the bloc and the other, being orthogonal, coming from the bevel angle between the two blocs.
Any idea ? or is a stupid remark?
I will try to remount the main sail, the one wich is too deept under windy conditions.
Claudio