Eric Scace wrote:
>
> I'm passing along tips from another competitive hobby of mine (racing
> catamarans):
>
> sealing the ends of rope:
> a) if the rope will melt under heat:
> -- wrap the place where the cut will be made in masking tape
> -- cut with a sharp knife in the middle of the tape
> -- apply flame (any source) to both ends to melt all fibers together.
> -- remove tape if you are fussy.
> b) if rope will not melt under heat, whip end of rope with waxed thread.
> Use sail needles, whipping thread, and a sailmakers palm. These are
> available at any marine store, or from websites (e.g., www.layline.com). If
> people need instructions for whipping line, I'll send them in a separate
> message.
>
> A separate note on the reflector made some glancing reference to
> hip-pocket engineering using rope in replacement of guy wire. On
> Olympic-class catamarans (Tornados), we have recently started replacing
> stainless steel standing rigging ('guy wires' for the mast) and trapeze
> lines with aramid fiber rope. This is extremely strong for a given
> diameter... very, very light... and does not stretch any more than steel
> under load.
Hi Eric,
Aramid is light, and aramid is strong, but aramid elongation is ever
equal to steel at the same size.
Most steel materials have an elastic modulus of around 29 Msi, Kevlar
49, used by all budget minded sailors (and hams) has an elastic modulus
of 18 MSI. Now, the guys with deep pockets can get Kevlar 149 cable
which has an elastic modulus of 25 MSI.
You may want to check this out on your own by collecting the information
from the manufacturers, or examine the "Guy Cable" link at the URL
listed below, to see how the manufacturers data compare. You can also
see a comparison of steel and aramid guy cable on a 100' tower at the
"Guyed Tower Study" link.
You can always get the aramid elongation to equal steel by going up in
size. This will increase the rigging drag, so you get to decide if the
weight aloft benefit is better than the drag when going upwind.
My company has built 22 rigs for America's Cup competitors, since 1992.
All of them have used aramid, or other synthetic cables for the running
rigging.
The higher elongation in the cable for runners and checkstays is not a
problem, because they are adjustable and can be adjusted to account for
the higher elongation, and still control the spar and enjoy the weight
savings.
Rules prevent active adjustment of the standing rigging while underway.
Many have played with aramid replacements. But, the vast majority favor
steel for standing rigging.
Glad to hear you are having a good time with the Tornado's, maybe the
reduced pitching moment on the cat with the aramid is faster, and the
increased spar deflection is not as important.
You can be sure that, size for size, the aramid is not as stiff as
steel.
Have fun!
73, Kurt, K7NV
YagiStress - The Ultimate Software for Yagi Mechanical Design
Visit http://www.freeyellow.com/members3/yagistress/
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