Annie Hill wrote:Arne has just posted the following under another topic.  This looks a very promising fabric.  In fact I remember looking at it myself some time ago, but dismissed it because it doesn't come in purple!

Might be heavy enough for SibLim, with good sailmaking practice, enough reinforcement at points of stress, a low-stress sailplan that's easy on the cloth?

A few days ago, Sebastian Hentschel, the German sail maker, sent me a couple of photos of junks he has made sails for, like this for his Peregrine  (now with black topsides!).

He uses a woven tarpaulin called Weathermax. It is said to hold the colour as well as acryl, but with the strength of polyester. At 230g/m² (Weathermax LT) and 270g/m² (Weathermax 80) these come without coating on any side.

I guess they are over the top for the little sail of Weaverbird, but I anyway think it looks like an interesting material for slightly bigger junk sails.

Two links:

Wethermax 80

http://www.leesailcovers.com/weathermax80/

Wethermax source with, with distributors in different countries.

http://www.safetycomponents.com/
WeatherMAX/Distributors/index.php?page=GreatBritain

Cheers, Arne

Polyester cloths, mostly dacron, mylar and various scrim cloths, have been used in the aircraft industry with consistent results. The factors that determine its life are UV and flutter, the latter being what sailors would consider localised, small scale flogging. Flutter causes a breakdown of the resin in dacron and rapidly leads to damage of the fibres. For the same reason a great deal of effort goes into minimising the creasing of the cloth during manufacture and assembling the surfaces. Annual cloth tests are performed using a tool called a Bettsometer, which essentially consists of a blunt needle with a handle that applies calibrated pressure - the cloth's ability to withstand a given needle pressure without puncturing gives a pass/fail result.

As the test itself is hard on the cloth, most wings have a small square test patch separate from the wing fabric but equally exposed to UV. It might be instructive for those experimenting with new cloths for sails to do something similar. It may help in determining how new cloths age and break down by distinguishing UV from tension stresses.

For what it's worth, UV in the mid-latitude, ozone-depleted environments of sunny NZ can knock out an aircraft wing in as little as a few thousand hours - pass the sunscreen, and get thee to shade...

I am inclined to get the most bang for my buck, so will spend now to save in the long run, but I know more than a few people who hate spending money, even to be better off long term (penny wise and pound foolish) and of course there are always those who can only lay hands on a finite amount at any one time.  I can imagine someone, half way round the world, with sufficient funds to get back home, but insufficient funds for new sails.  (One might say s/he shouldn't have ended up in that situation, but maybe s/he believed the sailmakers' claims of longevity!)  That being so, it's great to test out cheap cloth for emergency sails.  Of course, you will immediately see the flaw in my reasoning: if our sailor has a pointy rig, then there is no chance that s/he'll be making new sails from Tyvek or whatever.  If s/he has a junk rig, the situation is unlikely to arise!

And, of course, if s/he has the money for a new suit of sails, it would be as cheap to dump the pointy rig and change to junk (making the sail, of course.)

Annie,

sure, paying more money for the sail material is no guarantee that it is good, but the odds are improved. By the way, pointy rigs eat their sails, due to flogging and extreme stress (compared to junk sails), in particular on long offshore voyages. If I were dumb enough to plan a trans-ocean voyage with a pointy rig, I surely would add a squaresail for the downwind legs and keep those precious pointy sails well covered much of the time.

However, this is not only ocean voyaging versus pottering around the bay (my style), but also about the threshold of making a sail, all by oneself. You and I can sew up a new 30m²  junksail in around a week, no problem. However,  quite a lot of people are not so keen on making their own sails, so if they still decide to do it, they may just as well want the sail(s) to last, at least if they are to make bigger sails, meant for crossing oceans.

In addition, although small boats may get away with cheapo sail material, then small sails will be cheap anyway.

Arne

PS: I bet less than ten percent of the sailors in the world sail as far as 50000Nm in their whole life.