sails and seams

[vas]

Hi everybody...
Does anyone have an idea what the importance is of the direction of the seams of a sail? I have noticed that in a typical laser sail the seams have an angle to the boom, what would be the effect of having the seams parallel to the boom or however to another angle?
What would be the effect of having a sail made of one piece or less or more pieces??
Thanks,

 

[Murphs]

few issues here. (im by no means a sailmaker, i just find out what i can)

in general, you wouldnt want a seam across a high load point in a sail (lasers arent too bad, the sh*t quality of the dacron means the sail goes much quicker than the seam)
for instance there is high load around the clew of the sail so you wouldnt want a seam to be perpendicular to the load direction there

having panelled sails enables the sailmaker to control the shape of the sail (in a laser - not much)

so, having a one piece sail (unless its that 3DL yacht stuff) would be quite slow.

Im guessing you've never seen a laser radial sail, the seams in a radial sail go from the clew (end of the boom) to the luff (points up the mast)

 

[49208]

Traditional sailcloth (such as dacron used in Laser sails) is woven with threads (yarn) running in two directions - along the length of the roll (aka warp ) and across the roll (aka fill)

You can weave it using two different size yarns so that the material is stronger in the fill or warp direction. That's what is usually done for dacron material used in high aspect sails (where the luff length is more then 2 times the length of the foot)

If you use the bigger yarn in the fill direction the material is stronger (more resistance to stretch) across the roll of material and the opposite is true if you use the bigger yarn in the warp direction. A full size Laser sail uses fill oriented fabric and the radial uses warp oriented. (spinnakers and some low aspect headsails use a more balanced weave where the fill and warp threads are approx the same size)

The fabric is strongest when the loads are perfectly aligned (parallel) in the direction the threads are running. However once the load moves off axis, the fabric loses much of it's strength and stretches more. So, a sailmaker will try to align the fabric so that the strongest yarns are running parallel to the maximum load. In a mainsail the maximum load is a straight line between the clew and head. Since the Laser uses fill oriented material that means that the panels (seams) are roughly perpendicular to the leech.

If you made the sail with the panels parallel to the boom or foot, the load along the leech would be off axis and the leech would stretch and fall open (not fast)

There are many more factors that go into the design of the sail and use of the cloth to fit the design and there are tradeoffs when you are dealing with an unstayed, bendy mast such as the Laser.