Fabric Weight Questions

[fishbait]

I'm trying to understand how to correctly calculate fabric weight. Math is not my forte. But I'm going to give this a try. I located some Spinnaker Ripstop Nylon .75 oz a square yard. I'm looking at getting 9 yards, the cloth is 1.66 yards wide or 60"

If I calculate the overall weight with my rudimentary math skills:
9 x 1.66 ~ 15 Square Yards (actual is 14.94)
15 x .75 ~ 11.25 ounces (actual is 11.205)

Question 1: Is that correct?

I've seen some of you through some crazy formulas out there when figuring calculating the weights of tarps and hammocks

Question 2: Would you consider .75 oz Spinnaker strong enough for a 10 x 9 tarp?

[Detail Man]

Your math is correct. Having never worked with spinn, I can't answer question 2.

[Jimbo3b]

Your math appears to be correct. That's how I calculate.

I can't comment on the strength of the spinnaker cloth. I think that most people wanting to go that light have gone to cuben fiber.

In general, though, your goal is to gently translate any stresses from tieouts to the body of the fabric. Catenary cut edges should be a big help. A well-sewn hem (rolled or grosgrain ribbon) will also help.

[hangnout]

Most of the fabrics listed at .75 are weights before any coatings and/or could be listed as sailmakers yard (28.5x36) instead of square yard (36x36).

You will find that you probably are not getting waterproof fabric at .75 ounce a square yard in most cases.

[WV]

Spinnakers used to be coated to limit stretching on the bias. The coating resembled the urethane coating used for nylon tarps and rainwear, however spinnaker coatings were not waterproof. Then the technology evolved, and some spinn material had waterproof coatings, so people started making tarps out of it. Technology may have evolved some more, and waterproofness for a spinnaker may or may not be a bonafide survival trait.

Try to find out if the material you are considering is actually waterproof.

[FLRider]

+1 on testing the waterproofness; despite Spinn's light weight (and low stretch, at least for poly Spinn) quality, there's a reason that almost no one offers tarps in it nowadays. There were several batches that had quality-control problems associated with waterproofness.

Also, most of the stuff I've seen listed as 0.75 oz/sq yd coated is from kite sites. Kitebuilding sites often list weights in sailmaker's yards (so called from the supposed "largest practical" looms possible a ways back for sailmaking, due to materials technology to resist warping along the frame of the loom), which are smaller than square yards...despite being listed very similarly.

In other words, before spending mucho dinero on it, check the fine print and see if you can get a sample to check for waterproofness.

Hope it goes well for you!

[fishbait]

Thanks for the advise. The vendor I'm looking at is Sail Making Supplies at $11.62 for a linear yard I don't mind buy a 1 yard to test, if any thing I can always make a couple of stuff sacks from it. They also carry a 1.5 Spinnaker, I really wish they had more of a description on their WebSite.

[FLRider]

Thanks for the advise. The vendor I'm looking at is Sail Making Supplies at $11.62 for a linear yard I don't mind buy a 1 yard to test, if any thing I can always make a couple of stuff sacks from it. They also carry a 1.5 Spinnaker, I really wish they had more of a description on their WebSite.

While I've not actually contacted them regarding whether their weights are by square yard or sailmaker's yard, I'd assume the latter...considering that they're a sailmaker supply store. Which means that the "0.75 oz" fabric is probably actually ~0.947 oz/sq yd. Still lighter than most coated fabrics out there (about an half ounce/sq yd lighter than most 30d sil)...but it'd be worth checking, for sure.

Their phone number is listed on their "About Us" page; it may be worth giving them a call before purchasing. Most folks who have this specific of supplies are willing to talk about them, for sure.

Hope it helps!