On Jan 31, 9:35*am, "Garland Gray" wrote:
I need to replace some old plastic sheaves, and I have the option of sheaves
made of Delrin, acetal, or glass filled nylon. (I have learned that delrin
is acetal, *but don't know if all acetal sheaves are delrin).
So what are the relative attributes of acetal and glass filled nylon
sheaves? I read somewhere that GFN might be more abrasive on the pin, but I
assume that it is stronger. Ronstan sells both, but their website doesn't
solicit questions.

Nylon is very susceptible to UV degradation, but low friction. Don't
use it unless the part is both shielded from sunlight, and gets a lot
of running wear. Acetal is somewhat harder, better at resisting UV,
slightly higher friction, costs more.

It seems likely to me that a drop-in replacement for a specific sheave
will only be available in the material that specific mfg'r choses.

Fresh Breezes- Doug King

On Wed, 4 Feb 2009 12:44:31 -0800 (PST), wrote:

On Jan 31, 9:35*am, "Garland Gray" wrote:
I need to replace some old plastic sheaves, and I have the option of sheaves
made of Delrin, acetal, or glass filled nylon. (I have learned that delrin
is acetal, *but don't know if all acetal sheaves are delrin).
So what are the relative attributes of acetal and glass filled nylon
sheaves? I read somewhere that GFN might be more abrasive on the pin, but I
assume that it is stronger. Ronstan sells both, but their website doesn't
solicit questions.

Nylon is very susceptible to UV degradation, but low friction. Don't
use it unless the part is both shielded from sunlight, and gets a lot
of running wear. Acetal is somewhat harder, better at resisting UV,
slightly higher friction, costs more.

It seems likely to me that a drop-in replacement for a specific sheave
will only be available in the material that specific mfg'r choses.

Fresh Breezes- Doug King

It's also important to note that not all nylon is created equal. Nylon
not made specifically for the marine environment may absorb moisture
and swell over time.

"KLC Lewis" wrote in message
et...

"Wayne.B" wrote in message
...
When I was racing on big boats (50+ ft) most of the sheets and guys
had wire tails. With wire a metal sheave is absolutely necessary.


Wire tails on sheets have to be hard on the hands. But you're right,
they'd destroy plastic in short order.



I remember long ago, when I re-rigged by Cal 20 it had sheaves specifically
for wire. I switched to spectra and switched the sheaves to Delrin, which I
took to be the standard. I recall there are also aluminim sheaves that
accept both line and wire. Delrins are injection molded, so I'd think that
there might be some inconsistencies in them from time to time. I believe the
GFN sheaves are also injection molded but stronger. Looks like there are
also Delrin GFNs... :-)

http://www.jacoproducts.com/materials/thermoplastic.htm

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

"Capt. JG" wrote in message
.. .
I remember long ago, when I re-rigged by Cal 20 it had sheaves
specifically for wire. I switched to spectra and switched the sheaves to
Delrin, which I took to be the standard. I recall there are also aluminim
sheaves that accept both line and wire. Delrins are injection molded, so
I'd think that there might be some inconsistencies in them from time to
time. I believe the GFN sheaves are also injection molded but stronger.
Looks like there are also Delrin GFNs... :-)

http://www.jacoproducts.com/materials/thermoplastic.htm

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

Both my CT-41 (first boat) and my Rawson 30 (current boat) had wire crab
winches for the main and jib halyards when I bought them. The first thing I
did was to replace those wrist-breakers and get rid of all those fish hooks.
Now with the ultra-low-stretch super-strong lines being available in small
diameter, I have to wonder whether wire tails couldn't be replaced with the
new technology. No fish hooks, anyway. But I still loath crab winches.

"KLC Lewis" wrote in message
et...

"Capt. JG" wrote in message
.. .
I remember long ago, when I re-rigged by Cal 20 it had sheaves
specifically for wire. I switched to spectra and switched the sheaves to
Delrin, which I took to be the standard. I recall there are also aluminim
sheaves that accept both line and wire. Delrins are injection molded, so
I'd think that there might be some inconsistencies in them from time to
time. I believe the GFN sheaves are also injection molded but stronger.
Looks like there are also Delrin GFNs... :-)

http://www.jacoproducts.com/materials/thermoplastic.htm

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

Both my CT-41 (first boat) and my Rawson 30 (current boat) had wire crab
winches for the main and jib halyards when I bought them. The first thing
I did was to replace those wrist-breakers and get rid of all those fish
hooks. Now with the ultra-low-stretch super-strong lines being available
in small diameter, I have to wonder whether wire tails couldn't be
replaced with the new technology. No fish hooks, anyway. But I still loath
crab winches.



I was fortunate that the previous owner of the Sabre dealt with those sorts
of issues. How did you like the CT? I had a very pleasant trip on a slightly
larger version (48) some years ago. Didn't much like the hydraulic steering,
but other than that, it was a nice boat.

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

"Capt. JG" wrote in message
easolutions...


I was fortunate that the previous owner of the Sabre dealt with those
sorts of issues. How did you like the CT? I had a very pleasant trip on a
slightly larger version (48) some years ago. Didn't much like the
hydraulic steering, but other than that, it was a nice boat.

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

We had the pilothouse version, ketch rigged (I'm a dyed-in-the-wool
ketchie), 1972 model IIRC. It sailed very well, very seakindly and no bad
habits. Full keel, of course, very thick and heavy glass, displaced about
28,000 dry and empty. It had Edison quadrant steering, not hydraulic, and
rudder feel was adequate although I still prefer a tiller.

If I had it all to do over again, I wouldn't go pilothouse as it gives up
entirely too much living space for the inside helm which is of questionable
value. The pilothouse version also puts the engine under the saloon sole,
which is raised to accomodate it, which is the primary cause of the reduced
living space. And I would seriously inspect that puppy, looking for any
dryrot in the deck core and house -- ours was in bad shape and we had to
completely rebuild the deckhouse. But it's hard to beat a William Garden
design for good sailing. Kind of a handful for single-handing, though, as
she was rigged. But that could be fixed easily enough.

KLC Lewis wrote:
"Capt. JG" wrote in message
easolutions...

I was fortunate that the previous owner of the Sabre dealt with those
sorts of issues. How did you like the CT? I had a very pleasant trip on a
slightly larger version (48) some years ago. Didn't much like the
hydraulic steering, but other than that, it was a nice boat.

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

We had the pilothouse version, ketch rigged (I'm a dyed-in-the-wool
ketchie), 1972 model IIRC.

You know what they say about ketches. Once you've owned one, you'll
never own another one! Heh heh
Gordon, P365 ketch

KLC Lewis wrote:
"Garland Gray" wrote in message
...
Perhaps I didn't state that clearly. I place a high value on serious
replies here. I wasn't complaining over just one response, or the quality
of it.

I'm not asking others to make my decision for me; but why try to reinvent
the wheel ? The idea of newsgroups is to share experience, I assume.



From Brion Toss's book

Loads on the sheave itself are not so concentrated as those on the
bearing, but sheave material can be important relative to cost, weight,
and stability under load. Nylon, for instance, is very cheap and light
but can distort under heavy load. Worse, it swells when wet, increasing
sidewall friction. Delrin sheaves are more stable and nearly as cheap,
making a good medium duty sheave. Bronze, stainless, and aluminum
sheaves are heavy and expensive, but will stand up to extremes.

On sheave shape

Sheave score profile,
Semicircular for three strand and common braid.
Flat bottomed for kevlar
V grooved or semicircular with a notch for wire and rope

Gordon

"KLC Lewis" wrote in message
et...

"Capt. JG" wrote in message
easolutions...


I was fortunate that the previous owner of the Sabre dealt with those
sorts of issues. How did you like the CT? I had a very pleasant trip on a
slightly larger version (48) some years ago. Didn't much like the
hydraulic steering, but other than that, it was a nice boat.

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

We had the pilothouse version, ketch rigged (I'm a dyed-in-the-wool
ketchie), 1972 model IIRC. It sailed very well, very seakindly and no bad
habits. Full keel, of course, very thick and heavy glass, displaced about
28,000 dry and empty. It had Edison quadrant steering, not hydraulic, and
rudder feel was adequate although I still prefer a tiller.

If I had it all to do over again, I wouldn't go pilothouse as it gives up
entirely too much living space for the inside helm which is of
questionable value. The pilothouse version also puts the engine under the
saloon sole, which is raised to accomodate it, which is the primary cause
of the reduced living space. And I would seriously inspect that puppy,
looking for any dryrot in the deck core and house -- ours was in bad shape
and we had to completely rebuild the deckhouse. But it's hard to beat a
William Garden design for good sailing. Kind of a handful for
single-handing, though, as she was rigged. But that could be fixed easily
enough.

I like the ketch model also... almost bought a Pearson 356.

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

"Gordon" wrote in message
m...
You know what they say about ketches. Once you've owned one, you'll
never own another one! Heh heh
Gordon, P365 ketch

Ya, it's a "Ketch as ketch can" situation. lol