Marine Plastic

Dear all,

In the attached picture you can see the mainsheet truck for my father's Rustler Yacht.

While he was off on a long voyage one of the wheels split and so he affected a temporary fix with stainless steel washers. I would like some opinions of what the wheels could be made from so I can machine another. They function like the outer race of a ball bearing so it should be a simple enough job. The plastic needs to be hard wearing and needs to resist high loads without deforming. Any ideas?

My first 'port of call' would probably be PEEK : **LINK**

http://www.bpf.co.uk/plastipedia/polymers/PEEK.aspx

... It's not inexpensive, but has excellent properties.

MichaelG.

PEEK or PEK. Both high temperature polymers that machine well, look at the carbon fibre (CF) and PTFE filled bearing grades/varieties. Perhaps also partially glass fibre (GF) reinforced

Failing that UHMWPE, used for low friction applications.

Where did the original come from?

DickH.

I am very sure that the original rollers from the boatyard would not be PEEK , due to its' very very high cost, although it would probably do the job fine.

I would not recommend any sort of PE or PP, UHMW or otherwise, as the loads on a mast truck can be quite high. It is not up to this sort of job.

You might try acetal resin, 10% glass filled + PTFE filled if you can get it. One brand is Delrin. It is an engineering resin and will carry high loads especially if glass filled, has low friction, is easy to machine, is commonly available all over the world, and costs far less than PEEK although slightly more costly than PE or PP. Acetal is not hygroscopic , despite what some people think, and is great for marine use. Nylon is hygroscopic and not best for marine use, as it absorbs water over time and will lose strength, possibly cracking in time.

When you make a replacement set, make an extra set the sailor can stow in a ziploc bag in the rigging locker just in case. It's only a few extra minutes once you are set up, and could make a big difference on a bad day at sea.

To ID the original rollers' resin, try some solvent glue / plastic cement / ABS glue on a small area. If the dried glue will not stick at all, the resin is probably acetal. If it sticks a little, it might be a plain or glass filled nylon. You can also do a melt test on a piece of the roller sitting on a steel plate with a thermocouple next to it. Heat from below, gently, with a small gas torch or lighter. If the sample melts at about 180 deg C it may be nylon or acetal. If it melts at over 320 deg C it may be PEEK or other exotic high temp resin, possibly PPS or PVDF.

Edited By Jeff Dayman on 27/09/2018 22:32:15

Thanks for those replies! I was going to try delrin, simply because I had heard of it but I have never actually used it so I was unsure if it was applicable. The original was Lewmar and when my father contacted them about a spare, of course they told him it was discontinued and he would have to get a whole new mainsheet slide/truck assembly... We thought this was a cheaper, easier and more environmentally friendly option all round! I will purchase some delrin probably, and maybe look at PEEK, I am not paying for it so we'll see how deep my father's pockets are feeling! Any suggestions on where to get it?

Not sure in UK so I googled "acetal rod UK" .

For unfilled acetal homopolymer (best for bushings/rollers ) I found the link below - 7.44 UK pound for 1 metre of 20 mm dia rod.

http://www.plasticstockist.com/Delrin-Rod/Black-Delrin-Rod.aspx

For 20% glass filled acetal homopolymer my usual USA supplier has it at link below - I've asked for a quote. Note sure if it is available in small qty from UK vendors. Maybe try directplastics.uk

https://boedeker.com/Product/DELRIN-570-ACETAL

For better creep resistance, I would go along with filled polyacetal ... BUT ... machining glass-filled materials can give rise to issues where micro-fragments of glass can break away from the resin component and get under slideways.

While machining a bar of glass bead filled something or other, in an instant, my ML7 (Myford) saddle locked solid when glass beads found their way under it.

It required a total strip down and a thorough cleaning of the saddle and lathe bed.

Given the choice of colour, black usually offers more UV protection.

Although I'm like the idea of plastics, why not stainless steel?

Sam

As an after thought: wouldn't 'exposed' glass in the machined bore chew into the shaft?

Edited By Sam Stones on 28/09/2018 05:24:41

.

**LINK**

https://www.theplasticshop.co.uk/peek-index.html

MichaelG.

For a sailing-boat application, I'd consider Tufnol rod. Widely used for marine fittings, pulleys, rollers etc. Tough, weather resistant, easily machined and not too expensive.

Clive.

I made a set for my Squib mainsheet track using Oilon. Has lasted 2 seasons OK. Obviously much lighter load but as I had the oilon anyway I used it.Cheap & easy to machine.Purchased from Plastics Direct online who have a spec sheet there about that & the other materials already mentioned

I also made some oilon bearings for the wheels on our sailing club rescue boat trailer & they get sand & sea water every weekend. carry the weight of a RIB. They have lasted a season with no visible wear whatsoever so I have been asked to do the other 4 trailers this winter.

Edited By Sam Longley 1 on 28/09/2018 09:15:23

+1 for Tufnol

A delight to machine and the smell - aah! memories of my granddad's workshop.

Tim

If you Google around (mast, traveller, cars) the more modern versions of these things are quite interesting with recirculating precision ground delrin or torlon ball systems. The prices are eyewatering.

Someone once described yachting to me as standing under a cold shower tearing up 10 pound notes.

Two contributions, meant to be helpful:

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

Regarding Tufnol - a good material but you need to get the right grade. Fabric reinforced rather than paper and with the grain going the right way for the application.
See the Tufnol web-site, **LINK** .

Best regards,

Swarf, Mostly!

How do we get the right way, for the grain, when making gears (or wheels)? Or should we be laminating several thin layers before cutting the teeth?

.

Gears should be cut from sheet [plate?] ... but yes:

I do realise; that only gives two orthoganal axes of 'grain'

MichaelG.

Seeing as nylon is typically used for the wheels on most marine pulleys, doesn't that make nylon the obvious choice?

Neil

.

Give that the original [hopefully quite high spec] item has failed ...

I would be looking for something better than 'most'.

MichaelG.

Tufnol was/is used for many yacht fittings. Self lubricating and long lasting. So another +1 for Tufnol.

Dave
The Emerald Isle

So is it Whale brand Tufnol for sea water use and Carp brand for Freshwater use

Jason, I think that that is a Red Herring!

Howard