Marine Plastic

We don't know why it failed - it may have been subject to an unusual impact or load.

I'm assuming this is part of the mainsheet traveller, loads are pretty high, but if nylon was unsuitable for such rollers then it wouldn't be used.

Some digging suggests plain Nylon 6 might be best. Glass-filled nylon suffers brittle failure, while plain nylon requires extreme elongation before failing completely.

Why not ask Rustker yachts where they source the original - possibly worth replacing the whole unit if not just the wheels.

This one seems to use stainless steel bearings running on an aluminium track.

Or you could cough up £2.60 and buy a replacement wheel...

Edited By Neil Wyatt on 28/09/2018 12:47:41

Wow, I never expected all these responses! Thanks for the great suggestions. The originals are not nylon, as far as I can tell. They are extremely hard and don't have the 'slippery' sort of texture I associate with plain Nylon. they could of course be glass filled or something similar. From what I gathered of the failure, the wheel split and cracked in two so it suggests it was brittle. However, the whole boat and fittings are over 30 years old so failure is not surprising. A new track is possible, but they are not cheap and you have to make more holes in the deck, not to mention it is a very awkward area to reach to fit new bolts. I did wonder about stainless wheels but it is running on an aluminium track so I thought it might lead to excessive wear. However, the one Neil suggested does seem to use exactly that system. I will probably buy some lengths of different plastics and see which is most like the original, though I might just make four new wheels so as to reduce the risk of future failure if they are reaching the end of their lifespan. Anything I don't use will find a place in the 'bits box' for later!

Neil, I don't think the plain nylon wheel will manage to rotate sufficiently freely under the load of the sail. it needs the ball bearings to reduce the friction... Though, the replacement washers did work alright for a short space of time!

I'd test the Shore hardness of the part and ensure the replacement material was not too far from the original.

WARNING!

Re: Swarf, Mostly's contribution meant to be helpful:

Regarding plastic identification - Delrin (acetal) burns with an INVISIBLE flame.

With the greatest of respect for Swarf, Mostly! ...

But ..., whatever you do, DO NOT SNIFF THE FUMES!

Desk-top identification of plastics by burning (and sniffing), places polyactetal (Delrin) at the top of the DON'T DO list.

If you do, you'll never forget it.

Good luck with the rollers.

Sam

Sam Stone is correct, it's awful stuff if over heated.

Here's an extract from **LINK**

The flame is not self-extinguishing, shows little to no smoke, and the blue flame can be almost invisible in ambient light. Burning also releases formaldehyde gas, which irritates nose, throat, and eye tissues.

Enough said?

Sam

Another chilly morning in Melbourne

[another POM = polyoximethylene = polyacetal = acetal = Delrin]