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Marine Plastic

This topic has 27 replies, 16 voices, and was last updated 28 September 2018 at 23:18 by Sam Stones.

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27 September 2018 at 21:01 #373580
Barnabas Taylor
Participant
@barnabastaylor89961
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?
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27 September 2018 at 21:01 #29853
Barnabas Taylor
Participant
@barnabastaylor89961
27 September 2018 at 21:07 #373582
Michael Gilligan
Participant
@michaelgilligan61133
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.
27 September 2018 at 21:18 #373584
Dick H
Participant
@dickh
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.
27 September 2018 at 22:19 #373590
Jeff Dayman
Participant
@jeffdayman43397
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
27 September 2018 at 23:26 #373597
Barnabas Taylor
Participant
@barnabastaylor89961
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?
28 September 2018 at 01:33 #373600
Jeff Dayman
Participant
@jeffdayman43397
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
28 September 2018 at 05:20 #373601
Sam Stones
Participant
@samstones42903
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
28 September 2018 at 07:42 #373607
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Barnabas Taylor on 27/09/2018 23:26:18:

… 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?

.

**LINK**

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

MichaelG.
28 September 2018 at 08:54 #373613
Clive Brown 1
Participant
@clivebrown1
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.
28 September 2018 at 09:10 #373615
Sam Longley 1
Participant
@samlongley1
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
28 September 2018 at 09:22 #373616
Tim Rowe 1
Participant
@timrowe1
Posted by Clive Brown 1 on 28/09/2018 08:54:53:

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.

+1 for Tufnol

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

Tim
28 September 2018 at 09:31 #373617
Dick H
Participant
@dickh
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.
28 September 2018 at 09:42 #373619
Swarf, Mostly!
Participant
@swarfmostly
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!
28 September 2018 at 10:01 #373624
not done it yet
Participant
@notdoneityet
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?
28 September 2018 at 10:06 #373626
Michael Gilligan
Participant
@michaelgilligan61133
Posted by not done it yet on 28/09/2018 10:01:36:

How do we get the right way, for the grain, when making gears (or wheels)?

.

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

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

MichaelG.
28 September 2018 at 10:20 #373630
Neil Wyatt
Moderator
@neilwyatt
Seeing as nylon is typically used for the wheels on most marine pulleys, doesn't that make nylon the obvious choice?

Neil
28 September 2018 at 11:12 #373640
Michael Gilligan
Participant
@michaelgilligan61133
Posted by Neil Wyatt on 28/09/2018 10:20:58:

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

.

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

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

MichaelG.
28 September 2018 at 12:14 #373644
steamdave
Participant
@steamdave
Posted by Tim Rowe 1 on 28/09/2018 09:22:16:

Posted by Clive Brown 1 on 28/09/2018 08:54:53:

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.

+1 for Tufnol

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

Tim

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

Dave
The Emerald Isle
28 September 2018 at 12:21 #373645
JasonB
Moderator
@jasonb
So is it Whale brand Tufnol for sea water use and Carp brand for Freshwater use
28 September 2018 at 12:35 #373649
Howard Lewis
Participant
@howardlewis46836
Jason, I think that that is a Red Herring!

Howard
28 September 2018 at 12:38 #373651
Neil Wyatt
Moderator
@neilwyatt
Posted by Michael Gilligan on 28/09/2018 11:12:56:

Posted by Neil Wyatt on 28/09/2018 10:20:58:

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

.

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

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

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.
28 September 2018 at 12:43 #373656
Neil Wyatt
Moderator
@neilwyatt
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
28 September 2018 at 13:08 #373660
Barnabas Taylor
Participant
@barnabastaylor89961
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!
28 September 2018 at 20:07 #373714
Nick Hulme
Participant
@nickhulme30114
I'd test the Shore hardness of the part and ensure the replacement material was not too far from the original.
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