I've asked for some more information on this. The polypropylene rope specs
I find for 1/4inch are too low for safe winch launching, nominally 1150lbs,
which is less than the recommended weak link for say an L-23 or G-103. On
gliderforum.com, Pete Mulhare from the Whangarei GC describes the migration
from wire rope to a product described as spectra (but otherwise suggested to
maybe have been dacron in another thread though the images appear to be
Spectra) to poly rope. However, this is
3-strand 8mm, which is a tick more than 5/16inch, and a breaking strength of
1710lbs, according to specs I've found. Splicing is supposed to reduce
strength, however, from our experience with Spectra, the splices never
broke.

From a performance aspect, if we're seeking 2000-2500ft launches as the
norm, 3/16inch wire rope hangs about 32-40sqft of surface into the equation.
My rough estimate is that the total drag of the wire and tackle is at least
equal to and likely greater than a fully-loaded G-103 under the tension of
launch to 2000ft and substantially more above that release height. The
higher the launch, the greater the effect of the rope diameter. 5/16inch
may be fine for short runs and moderate launch heights, but there even more
rope drag effect if high launches are the goal. Amsteel Blue would seem to
be the product of choice, but it's smallest available diameter is 3/16inch.
There are a couple of other products with 2800lb breaking strength at
1/8inch diameter. The cost of most products can be accomodated IF a length
will go 1000 launches. The weight advantages are a given.

Frank Whiteley
Colorado

"Charles Yeates" wrote in message
...
The Auckland Gliding Club in NZ has been using 1/4 inch poly on their
winch for at least two years -- contact them for comments through

http://www.gliding.co.nz/

Robert Curry wrote:
With all the talk about Spectra for winch wire replacement, one thing
comes to mind. COST! I just replaced our armored cable with 7X19
3/16 inch stranded steel cable. The cost for a five thousand foot
spool was $500. If the Spectra costs 40 cents per foot that equals
$2000. I recently heard of a club that was using standard poly rope
to replace their wire. They were claiming 2000 foot tows on a 4000
foot runway. Does anyone know where this operation is and if they
were using 1/4 inch poly or a beefer size? I wouldn't think that 1/4
inch poly would last very long.