Sail Construction

by Geoff Moore, 2008..

Carol submitted a question to me and I thought I would share it with the listserve.

Her question was, what is x-ply? Here is today’s primer on sail construction...

Monofilm is a single layer of plastic, and is what most sails are made of these days. The reason it is used is that it is light, strong, and doesn’t deform it’s shape. This helps make the sail very stable, because it doesn’t stretch and change the shape of the foil. Battens and cams also serve this function of maintaining a stable shape.

X-ply is the monofilm equivalent of “rip-stop nylon”, and is two layers of monofilm bonded together (glued), with a criss-cross weave of kevlar thread in between layers. It has advantages and disadvantages.

It is slightly heavier than monofilm. It is much more resistant to crinkling, and thus creating the basis for cracks in the monofilm. The x-ply weave further prevents the monofilm from failing catastrophically if it gets punctured / dented by falling on it, etc. X-ply is extremely strong under tension.

If one assiduously takes care of a monofilm or x-ply sail (keep it out of sand, doesn’t wrinkle the film, etc.), then the real killer of monofilm is UV light. I’ve heard claims that x-ply is more resistant to UV because of the GLUE layer, but in practice I haven’t seen it be so impressive that I wouldn’t buy monofilm – especially if the goal is to have a light weight sail. When x-ply starts to fail from UV, what you get is small cracks and holes between the threads.

Wave sails are often made almost totally of x-ply (except for the mast sleeve) because it is anticipated that the sailor will fall in the “tumble-dry” section of the wave (aka “impact zone”), and the wave will pound the sail with it’s own weight and on the bottom (which may have coral or other things unfriendly to monofilm). Unless a CWC member intends to sail Seneca on a storm from the south, or Ontario on a 20+ mph day, nobody from CWC truly “needs” a wave sail. However, wave sails also tend to have higher foots (to stay out of the foam/wave face), shorter clews, and are easier to handle.

Other sails typically use x-ply in areas where the fabric (monofilm) is under lots of tension and needs to be resistant to tearing.

Ezzy sails are now totally made of x-ply because they have made some design features that make the sails both light and strong.

The Hot Sails Maui SuperFreak is totally made of dacron; it is unique and I won’t go into the SuperFreak now. Perhaps later.

Other materials are PVC film, which is sometimes used for the window.

Another important fabric in the sail is the mast sleeve. There is a lot of friction / pressure here, so a durable fabric extends the life of the sail. Race sails typically have very light weight luff-fabric, because extra weight here doesn’t make you go faster. So race sails often wear out here. Race sails are heavy, though, because they have lots of cams and battens. Many newer sails have some particularly heavy weave and very tough fabric in the mast sleeve, because this part of the sail rubs against the grit on the deck of the board and rapidly abrades the fabric and stitching at the tack and foot.

In the event of a mast failure (been there, done that 3 times), the jagged ends of the broken mast shred the mast sleeve. This can be repaired fairly easily, but it is a total nightmare getting back to shore. You can’t get the mast out of the sleeve because the fibers of the mast are snagged in the fabric, it of course never happens when you are lightly powered but rather when it’s windy and the waves are pounding you, you don’t want to just paddle it in without unrigging in the water, because the sleeve repair in itself is actually a pretty small job, but if waves and mast segments are allowed to flap around it will totally shred the sail beyond being worth the expense of repairing it. Having been there, done that, I always buy a sail that has a tough mast sleeve. I also don’t skimp on masts, because I don’t want to have another day where I’m swimming around in the water, trying to save myself and my stuff with nobody to help.

Lastly, there are a variety of niceties that companies put on sails – tack pulleys, downhaul handles, elastic ties for rolling it up, neoprene pads on the foot (gentle on tender shins), etc. One reason I like Hot Sails Maui is that their sails have all of these user-friendly features.

BTW – once I was in Hatteras and broke a mast, with LOTS of sailors all over, passing me by, and for 20 minutes nobody bothered to stop and help. Finally, Petra Kanz, an ABK instructor now at Lakes Bay, stopped and towed me back in. If a sailor looks like they are in the water and not getting back up again, ALWAYS go see if they need help.

Again, one message I cannot reinforce enough is – buy the best mast you can afford.

GEM