On Sat, 10 May 2008 14:22:24 -0500, Brian Whatcott
wrote:


There's a board used in aircraft still - been round for ever, that
looks like SRBP (synthetic resin bonded paper) that is called SRBF
where the fabric layers are made of linen. It's used for cable
fairleads. It turns out it has an unexpected property - it is durable
against frictional wear because it is self-lubricating. Who would have
guessed?

When I have proposed high density polyethylene for similar purposes
I have heard something like "we KNOW this works, how long does HDPE
last?". You can buy HDPE cutting boards at Walmart for peanuts -
and SRBF is expensive and hard to gert any more, But the Cape Horn
plastic bush story make this jump right back to mind!
(Nylon swells and weakens I believe?)

Brian Whatcott Altus OK

FWIW - my experience

Nylon should not be used for underwater or near water bushings as it
has a tendancy to swell and thus tighten on the shaft.

I had the bottom and top bushing for my rudder made of HDPE and they
are still going strong - no swelling, no wear, no friction after 15
years in the water. It is the modern lignum vitae (sp?)

So far as I am concerned, the stuff is magic. You can drill it, saw
it, file and chisel it and can thus make a myriad of thing about the
boat. It is also cheap and readily available I find that the most
useful is an offcut slab of 20mm (0.75") which I was given from a
waste offcuts bin.

In addition to the inflatable I have a hard GRP 9' 6" dinghy which
breaks into two nesting halfs. In Australia I had to change the wooden
keel rubbing strake sometimes 6 monthly as nothing seemed to resist
the worms' boring activity, the dinghy being almost permanently in the
water. I tried Iron Bark and most other suggestions from the old
hands. I through bolted a length of HDPE to both halves and it is
still going stronge, sharp coral has no effect and even the barnacles
do not attach to it. Fantastic stuff.

The homeware shops and supermarkets sell breadboards which vary in
thickness from 2mm to about 12mm (0.5"). This stuff does not seem as
dense as the industrial HDPE I have but it comes in very useful as
washers, packers, shims, and anything else requiring a hard, cutable
inert and non-conductive material. I always carry a couple of
different sizes on board now.

regards
Peter