Are sail panels edges flat or have some taper (seam shaping)?

maybe someone has pictures of panels separetly?

How get sail profile from flat material?

usually where one panel meets the other, one panel will have positive shaping and the other seam is flat. Nearer to the top of the sail some sail makers will use negative shaping to get twist while some rely on a straighter luff curve or a large roach.

Use some double sided tape and paper to play around with it is the best way to get an idea of how it works.

Guessing combination of seam shape battens and mast

Cammed windsurfing race sails are flat out of the bag. They only get 3D shape when you insert a mast and apply downhaul tension and engage the cams. It's a mystery to me how this happens

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Madge said..
usually where one panel meets the other, one panel will have positive shaping and the other seam is flat. Nearer to the top of the sail some sail makers will use negative shaping to get twist while some rely on a straighter luff curve or a large roach.

Use some double sided tape and paper to play around with it is the best way to get an idea of how it works.

If connect race sail at head cap with rope to tree and pull pulleys at other side,so to get sail in tension,will sail get belly or will be stay flat like without tension?

If yes,how tension transform flat sail into belly profile,what is physics behind this?

Hotlap.....Shape is added to sails via the seams, either vertical and horizontal. Also with luff round ( the curvature of the luff is greater than the mast bend) The seams have curvature so when sewn together they push 3D shape into the sail. To visualise it do this. Grap 2 pieces of A4 paper. On one piece of paper cut a shallow curve on one edge. The tape the 2 pices of paper together lining up the curved edge with the straight edge. You will see how it pushes 3D shape into the paper when taped together.
This is how sails are done.

Regards Martin

OH...and looking at your question closer...how to make profile out of flat sheets?......If you design a sail without any seam shape then the only way you can add profile is with luff round. So luff round is where you add more curvature to the luff than the amount of mast bend...This does the same thing as what I explained with the paper example. If you shape a sail with luff round alone the only way you can control the position of the 3D curvature is with the battens. So the battens are tapered and this taper dictates the shape of the profile.
You will find most windurfing sails use all 3, Horizontal seam shaping, vertical seam shaping and luff round with designers deciding how much of each they will use.

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mr love said..
OH...and looking at your question closer...how to make profile out of flat sheets?......If you design a sail without any seam shape then the only way you can add profile is with luff round. So luff round is where you add more curvature to the luff than the amount of mast bend...This does the same thing as what I explained with the paper example. If you shape a sail with luff round alone the only way you can control the position of the 3D curvature is with the battens. So the battens are tapered and this taper dictates the shape of the profile.
You will find most windurfing sails use all 3, Horizontal seam shaping, vertical seam shaping and luff round with designers deciding how much of each they will use.

thanks mr love, that was very informative.

its pretty simple, all the sail shape is done through seam shape under the battens, the edge of the seam is curved, well its actually about 3-4 straight lines as curves are to hard to connect. All sails are done like this even cambered sails.

The panels and seams that run from the tack to the top of the sail are for load distribution. All the rest are for looks or to try to make the stronger or reduce weight in certain areas, yes you can make a sail that looks very plain that will rig the same as one with all the fancy shapes panels.

The mast curve is what gives the sail skin tension and also controls leech tension, something as simple as adding or removing 20mm of mast curve to the top 1/4 of the sail can make a big difference.

The skill and trick is to get all these to work together, a few mm here and there could make a sail amazing or terrible.

And then to confuse you, you have Northsails (for yachts) with their 3DL technology
The sail is molded in shape, in one piece.

Sorry to correct you PC but not all sails are shaped with horizonal seam shape under the battens. some sails are shaped majority vertical seaming like the Pryde Race sail shown earlier in the thread. Also shape is added with luff curve ( which also impacts twist). You will find most sails use a combination....some favouring vertical shape and others horizontal. It depends what the designer is trying to achieve.

There is an excellent insight into this here from legendary sailmaker, Phil "Bugs" Smith of Avalon Sails: www.seabreeze.com.au/forums/Windsurfing/Review/Avalon-Sails-XTR-7-0?page=2

Ezzy Sails are also formed with a different design concept than many other windsurfing sails. That means, when you tension the batten, the sail shape comes from the batten taper plus the profile in the seam. The result is a defined, exact, horizontal profile. These sails are the exact opposite of most other sails that have very little shape in the panels and most of the shape coming from the excess luff curve.

Dave Ezzy on sail design:

www.ezzy.com/rig-support/ezzy-basic-sail-design-theory/

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mr love said..
Sorry to correct you PC but not all sails are shaped with horizonal seam shape under the battens. some sails are shaped majority vertical seaming like the Pryde Race sail shown earlier in the thread. Also shape is added with luff curve ( which also impacts twist). You will find most sails use a combination....some favouring vertical shape and others horizontal. It depends what the designer is trying to achieve.

the body of that sail would be made the same as every other sail, sails are made in sections, then joined under the batten pockets, that Pryde add is saying there are continuous panels at the front of the sail,that don't necessarily mean they are one piece of material, the add even shows that those panels are joined, the front 3 even show joins under the batten pockets.

Yes i have made sails before and even race sails.

It says continuous panels to eliminate horizontal seams in the highly loaded leading edge. No horizontal seams means no horizontal shape..it is done vertiaclly under the sleeve pocket. And by the way I know for a fact that one sail brand uses a combination of horizontal and vertical seaming, some with very litlle horizontal seam shape. How do I know....I design them.
The lines you see on the front panels in the add drawing drawing are from the CAD program which draws the centerline of batten on the panel even if it is a vertical one piece panel.

Back to the origanal question.....here is a great example of making shape from flat materials. Sails use the same method of attaching curved panels together to create shape.

The way I understand it from rigging a few times is...

The mast is tapered so as the mast is squeezed inside the sail the top part excess sail material starts to wrinkle.

The width of the lower panels creates a pocket more or less deep. The wider the panels the deeper the pocket.

The more downhaul the lower and smaller the pocket.

When the wind fills in the sail, the panel stretch and the battens move in and out besides the mast.

Ezzy has battens that taper and under tension pop in one direction or the other a bit like what cams do. This gives the shape and battens do not need to protude besides the mast. This makes the sail more stable but also a touch heavier when neutral.

Good question hotlap. I assume all sail manufacturers simulate their sails on commercially available software ?, and this software produces the cutout templates ?

If you check your own clothes then you'll find that seam shaping and darts allow the flat cloth to fit around your curves.
The stretch in the material also allows some localised variation.

A flat piece of material generally stretches better across the 'bias' than it does in the 'warp' or 'weft' direction.

The same principles apply when sail making.


Most sails start from flat panels but you can be fooled by colourful windsurf sails with extra seams which are mostly cosmetic.
Some extra seams are also there to minimise the material used off an expensive roll of sail cloth.

The shape in our windsurfing sails comes from broadseaming - like the darts in your clothes - but the fullness at the lower part of the sail comes from luff round, which is cut to be a deliberate mis-match with the mast bend curve.

If you only use the mis-match of luff round to add fullness to the sail then the shape tends to have fullness further aft - and we want the sail to approximate to an aerofoil shape with the maximum draft set forwards of the centre.
So the 'broadseaming' or darts in horizontal panels can ensure that the sail draft remains forwards, and that broadseaming in the luff seams adds fullness and shape behind the masts which helps the sail drive be forward-pulling.
The head of the sail is cut flatter because it twists open to release excess power and that twist also allows the luff panel to match the angle of the wind at the top of the rig.

The sail battens added are tapered, not some much to add shape, but to encourage the sail to keep the shape cut in place by the designer.

We can contrast the approaches of different designers and it has already been pointed out that with Ezzy sails the sail shape comes almost solely from broadseaming, and not from mis-matched luff round.
My own Severne sails have minimal seams to reduce sail weight and the sails set with good rotation. But behind the batten pockets there is some subtle broadseaming which ensures extra shape in the front third of the sail, and that keeps the sail driving forwards.


It's maybe worth adding that slalom and race and blasting sails work best if they are forward-pulling (for speed and to help get you upwind), whereas some wave sails have the maximum draft set further back so that they a relatively more sideways pulling - and this is to help load the backhand for DTL riding.

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Basher said..
If you check your own clothes then you'll find that seam shaping and darts allow the flat cloth to fit around your curves.
The stretch in the material also allows some localised variation.

A flat piece of material generally stretches better across the 'bias' than it does in the 'warp' or 'weft' direction.

The same principles apply when sail making.


Most sails start from flat panels but you can be fooled by colourful windsurf sails with extra seams which are mostly cosmetic.
Some extra seams are also there to minimise the material used off an expensive roll of sail cloth.

The shape in our windsurfing sails comes from broadseaming - like the darts in your clothes - but the fullness at the lower part of the sail comes from luff round, which is cut to be a deliberate mis-match with the mast bend curve.

If you only use the mis-match of luff round to add fullness to the sail then the shape tends to have fullness further aft - and we want the sail to approximate to an aerofoil shape with the maximum draft set forwards of the centre.
So the 'broadseaming' or darts in horizontal panels can ensure that the sail draft remains forwards, and that broadseaming in the luff seams adds fullness and shape behind the masts which helps the sail drive be forward-pulling.
The head of the sail is cut flatter because it twists open to release excess power and that twist also allows the luff panel to match the angle of the wind at the top of the rig.

The sail battens added are tapered, not some much to add shape, but to encourage the sail to keep the shape cut in place by the designer.

We can contrast the approaches of different designers and it has already been pointed out that with Ezzy sails the sail shape comes almost solely from broadseaming, and not from mis-matched luff round.
My own Severne sails have minimal seams to reduce sail weight and the sails set with good rotation. But behind the batten pockets there is some subtle broadseaming which ensures extra shape in the front third of the sail, and that keeps the sail driving forwards.


It's maybe worth adding that slalom and race and blasting sails work best if they are forward-pulling (for speed and to help get you upwind), whereas some wave sails have the maximum draft set further back so that they a relatively more sideways pulling - and this is to help load the backhand for DTL riding.

You are sailmaker,where did you work?
Does sail company made their mast by themslef or masts are made by other companies?

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hotlap said..
Are sail panels edges flat or have some taper (seam shaping)?

maybe someone has pictures of panels separetly?

How get sail profile from flat material?

In the same way that you can build any 3D structure by stitching together 2D panels that are not rectangles.

Here is a old article I did about making a sail. Basically the shape comes from joining a straight bit of material to a curved bit.
sailrepair.co.uk/making-a-sail/