On Fri, 15 Aug 2008 11:45:07 -0700, in message
ons
"Capt. JG" wrote:

Which line do you think you could put more tension on before the line
breaks? The furling line or the jib sheet? Seems to me that most people
would have plenty of experience putting jib sheets under a lot of tension,
yet would not put a lot of tension on a furling line. It's a lot easier to
put more tension on a jib sheet, which could lead to furling line failure.

For an example, a 5/16" StaysetX furling line has a tensile strength
of 3000 lbs, while a 1/2" StaysetX jib sheet has a tensile strength of
8500 lbs. Allowing for the mechanical advantage produced by the
furling system[1] it would be hard to say which would fail first. My
suspicion is that you would do major damage to your sail before either
line would fail.

I agree that loading up the sheets of a furled jib using the
mechanical advantage available with a handle in the winch would be a
bad idea.

Ryk


[1] In a typical drum system the torque loads will balance between the
sail load and the furling line. When the sail is fully out there is no
torque, thus no furling line load. When partially or fully furled the
sail load will produce a torque of approximately the wrap radius times
the sheet tension, while the furling line will produce a torque of the
furling line tension times the drum radius (plus any remaining wraps
of line). The result is that the maximum tension in the furling line
is probably 1/4 to 1/2 the tension in the jib sheet and considerably
less when the sail is only partially furled.

On Fri, 15 Aug 2008 17:12:51 -0400, Ryk
wrote:

I agree that loading up the sheets of a furled jib using the
mechanical advantage available with a handle in the winch would be a
bad idea.

Isn't that exactly what happens during normal sailing?.. (reefed)

On Fri, 15 Aug 2008 22:24:51 +0100, in message

Goofball_star_dot_etal wrote:

On Fri, 15 Aug 2008 17:12:51 -0400, Ryk
wrote:

I agree that loading up the sheets of a furled jib using the
mechanical advantage available with a handle in the winch would be a
bad idea.

Isn't that exactly what happens during normal sailing?.. (reefed)

Not quite. When fully furled the sheet loads are applied to the foil
as a nearly point load, rather than distributed.

Ryk

On Fri, 22 Aug 2008 13:34:14 -0400, Ryk
wrote:

On Fri, 15 Aug 2008 22:24:51 +0100, in message

Goofball_star_dot_etal wrote:

On Fri, 15 Aug 2008 17:12:51 -0400, Ryk
wrote:

I agree that loading up the sheets of a furled jib using the
mechanical advantage available with a handle in the winch would be a
bad idea.

Isn't that exactly what happens during normal sailing?.. (reefed)

Not quite. When fully furled the sheet loads are applied to the foil
as a nearly point load, rather than distributed.


Fair cop, although you have moved the goal posts a bit to consider the
bending stress on the foil or the forestay tension rather than just
the stresses associated with twisting of the foil. I am amazed that
roller furling foils cope at all..

"Ryk" wrote in message
...
On Fri, 15 Aug 2008 11:45:07 -0700, in message
ons
"Capt. JG" wrote:

Which line do you think you could put more tension on before the line
breaks? The furling line or the jib sheet? Seems to me that most people
would have plenty of experience putting jib sheets under a lot of tension,
yet would not put a lot of tension on a furling line. It's a lot easier to
put more tension on a jib sheet, which could lead to furling line failure.

For an example, a 5/16" StaysetX furling line has a tensile strength
of 3000 lbs, while a 1/2" StaysetX jib sheet has a tensile strength of
8500 lbs. Allowing for the mechanical advantage produced by the
furling system[1] it would be hard to say which would fail first. My
suspicion is that you would do major damage to your sail before either
line would fail.

I agree that loading up the sheets of a furled jib using the
mechanical advantage available with a handle in the winch would be a
bad idea.

Ryk


[1] In a typical drum system the torque loads will balance between the
sail load and the furling line. When the sail is fully out there is no
torque, thus no furling line load. When partially or fully furled the
sail load will produce a torque of approximately the wrap radius times
the sheet tension, while the furling line will produce a torque of the
furling line tension times the drum radius (plus any remaining wraps
of line). The result is that the maximum tension in the furling line
is probably 1/4 to 1/2 the tension in the jib sheet and considerably
less when the sail is only partially furled.



I suspect you'd do major damage to the furling mechanism before either
broke.


--
"j" ganz @@
www.sailnow.com