Frankly, I thought I'd get a better answer here.
It's really moot now, because I have a choice of GFN for only one size
sheave(I need 3 different sheaves) . I'll probably get it and try it because
the size might be better than the closest acetal sheave.

"Wayne.B" wrote in message
news
On Sat, 31 Jan 2009 09:35:42 -0500, "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.

Why not give Ronstan or your local rigger a call and find out the pros
and cons of each?

"Garland Gray" wrote in message
...
Frankly, I thought I'd get a better answer here.
It's really moot now, because I have a choice of GFN for only one size
sheave(I need 3 different sheaves) . I'll probably get it and try it
because the size might be better than the closest acetal sheave.


My most humble apologies for not being able to give you the answer you
sought.

Seriously, this is one of those, "You pays your money, you takes your
chances," sort of decisions that nobody else can really make for you. I
thought the suggestion from someone else to talk to your rigger about it was
spot on. For my own part, I don't like putting plastic parts anyplace where
I can't inspect them on a regular basis, and would always choose metal
sheaves if at all possible.

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.

"KLC Lewis" wrote in message
et...

"Garland Gray" wrote in message
...
Frankly, I thought I'd get a better answer here.
It's really moot now, because I have a choice of GFN for only one size
sheave(I need 3 different sheaves) . I'll probably get it and try it
because the size might be better than the closest acetal sheave.


My most humble apologies for not being able to give you the answer you
sought.

Seriously, this is one of those, "You pays your money, you takes your
chances," sort of decisions that nobody else can really make for you. I
thought the suggestion from someone else to talk to your rigger about it
was spot on. For my own part, I don't like putting plastic parts anyplace
where I can't inspect them on a regular basis, and would always choose
metal sheaves if at all possible.

On Tue, 3 Feb 2009 20:35:39 -0500, "Garland Gray"
wrote:

The idea of newsgroups is to share experience, I assume.

In a way, that is what I was doing. Perhaps I'm fortunate to have a
really good rigger that has given me a *lot* of incredibly good advice
over the years. He sees hundreds of different boats and rigging
issues every year, getting far more experience with such things than I
ever will. He also has a direct pipeline to all of the engineering
folks behind the different products that he services.

On Tue, 3 Feb 2009 20:35:39 -0500, "Garland Gray"
wrote:

The idea of newsgroups is to share experience, I assume.

In a way, that is what I was doing. Perhaps I'm fortunate to have a
really good rigger that has given me a *lot* of incredibly good advice
over the years. He sees hundreds of different boats and rigging
issues every year, getting far more experience with such things than I
ever will. He also has a direct pipeline to all of the engineering
folks behind the different products that he services.

"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.


Well, FWIW Harken uses Delrin sheaves in most, if not all, of their midrange
and smaller blocks, and at least many of their Big Boat range as well. I'm
not sure if they use metal sheaves at all any more. I've used their blocks
for the past fifteen years and have never had one fail on me. The delrin
cheeks will discolor over time, going from black to dark grey, but it
doesn't seem to harm them. I like Garhauer for their "all metal" policy, but
I have bought quite a few Harkens over the years and have never regretted
it. You can get them about anywhere there's boats, and there's a lot to be
said for that convenience.

On Tue, 3 Feb 2009 22:15:06 -0600, "KLC Lewis"
wrote:

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.


Well, FWIW Harken uses Delrin sheaves in most, if not all, of their midrange
and smaller blocks, and at least many of their Big Boat range as well. I'm
not sure if they use metal sheaves at all any more. I've used their blocks
for the past fifteen years and have never had one fail on me. The delrin
cheeks will discolor over time, going from black to dark grey, but it
doesn't seem to harm them. I like Garhauer for their "all metal" policy, but
I have bought quite a few Harkens over the years and have never regretted
it. You can get them about anywhere there's boats, and there's a lot to be
said for that convenience.

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.

"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.

"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

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