Sail sun protection

[TIM WEBB]

The basic formula we use in the parachute industry is 2 weeks in direct sun = 50% loss in strength. Of course, we pad the <beep> outta this formula for safety, but it pretty much applies to any nylon/dacron/etc. material. Unfortunately, there are many similarities: both sailors and skydivers use their equipment when the sun is shining, therefore the same conundrum applies.

[ChrisB]

Scott,

I would leave the sock on the jib and the cover on the main until the first sail of the weekend and then not worry about re-covering the jib. The bird forces your hand on covering the mainsail.

Chris

[GreenLake]

Tim,

Nylon is more sensitive to UV than polyester (Dacron). And you do see people go on offshore passages longer than 2 weeks. So I wonder when you reach the 50% point with Dacron sails - could be that sail cloth is different from parachutes in ways other than just the fiber. Everybody cites the difference in UV resistance, but this graph from Wikipedia is the closest thing I've come to finding numbers:



Polyester and Nylon are on the right, the graph shows UV resistance relative to Kevlar (=100%).

[TIM WEBB]

You (and Wikipedia) are correct GL. I was just making a general comparison. With parachutes, the canopy portion is almost always Nylon, with very few exceptions. Lines are usually Spectra, Dacron, Vectran, or Kevlar, while containers (the "backpack") are usually Cordura or Parapack (Nylons). The latter can be treated with UV protection, whereas the canopy/lines cannot, but the container also tends to see more sun exposure (walking around the DZ, waiting in the boarding area, etc). Harnesses are made of Nylon webbing, but they are required by the FAA to be like 10 times stronger than they need to be (and drop tested to prove it!), so loss of strength there isn't really ever an issue. It's usually abrasion or damage from acid or whatever that does a harness in ...

For sails, perhaps a better comparison would be between, say, Dacron mains and jibs, and Nylon spinnakers/headsails?

[Breakin Wind]

Scott,

I would leave the sock on the jib and the cover on the main until the first sail of the weekend and then not worry about re-covering the jib. The bird forces your hand on covering the mainsail.

Chris

Thanks Chris, It does sound like a reasonable compromise, however I guess I do need to get back to reality a bit and consider that last summer I measured my "launch prep" time in the long side of 1/2 hour (even with the boat at the dock 24/7) and now I'm whining about the 4-5 minutes it takes to pull down the sock and stow it. (and I guess the 4-5 minutes on the other end to put it back up).

Next thing ya know, I'll want to have the boat already untied and ready to push of as I walk from the cabin to the dock so I can just step on and go...

For that, I would need a dock boy? Wouldn't that get the neighbors talking...

Thanks - Scott

[GreenLake]

With parachutes, the canopy portion is almost always Nylon, with very few exceptions. Lines are usually Spectra, Dacron, Vectran, or Kevlar, while containers (the "backpack") are usually Cordura or Parapack (Nylons). The latter can be treated with UV protection, whereas the canopy/lines cannot, but the container also tends to see more sun exposure (walking around the DZ, waiting in the boarding area, etc). Harnesses are made of Nylon webbing, but they are required by the FAA to be like 10 times stronger than they need to be (and drop tested to prove it!), so loss of strength there isn't really ever an issue. It's usually abrasion or damage from acid or whatever that does a harness in ...

For sails, perhaps a better comparison would be between, say, Dacron mains and jibs, and Nylon spinnakers/headsails?

I know standard sailcloth uses fillers, mainly to make the cloth stiffer; presumably they also add to the UV resistance, but I couldn't find anything definite on that. For laminate sails, they definitely add coatings to reduce the effects of UV exposure on the fibers. I imagine none of that is done for parachutes.

[ChrisB]

Next thing ya know, I'll want to have the boat already untied and ready to push of as I walk from the cabin to the dock so I can just step on and go...

For that, I would need a dock boy? Wouldn't that get the neighbors talking...

If you really want to get the neighbors talking, I'd recommend a "dock girl", but that would probably get the wife talking too. You're already ahead of most of us as your boat is already in the water with the mast rigged.

[UCanoe_2]

My mainsail cover is a few inches short, so I use a feed sack to cover the rest of the sail. My late boating buddy Paul used the sack to bring a very fresh chicken dinner on one of our canoe trips.

[TIM WEBB]

I know standard sailcloth uses fillers, mainly to make the cloth stiffer; presumably they also add to the UV resistance, but I couldn't find anything definite on that. For laminate sails, they definitely add coatings to reduce the effects of UV exposure on the fibers. I imagine none of that is done for parachutes.

Correct: the Nylon fabric of a parachute canopy will undergo hundreds if not thousands of, frankly, quite violent openings during it's typical lifespan (even a "normal" opening, while quite non-injurious to the jumper, is hell on the canopy). The only treatment that really works with any degree of success is a silicone impregnation of the fabric, as well as heated calendaring (flattening of the fibers, thereby reducing the air space between them) that is used to make the zero-porosity fabric common on main canopies today. Being ZP makes the airfoil more aerodynamically efficient. All that does nothing to combat UV tho. But as far as any external coatings? Fuhgeddabouddit! They come off within the first few deployments. That's why any sort of graphics or art/logos done on canopies have to be either more fabric sewn on/appliqued (a very tedious, expensive process, as you have to account for all the seam allowances between cells), or large-format dye sub printing, which is also very expensive, but showing a lot of promise. Screen printing is right out!

But again, the upside is that that canopy only sees about 2-5 minutes of direct UV exposure each jump. Unless the user is an idiot who packs it in the direct sun, or leaves it in their trunk all the time!

Now, paragliding canopies, which don't go through a deployment every time they're used, but spend a lot more time in the sun, are another story, and they are making huge advances with those things.