Plastic Sea Cocks

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nathanlee

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Sounds a bit like a purchase from Ann Summers, but alas, no.

I'm considering replacing all the seacocks on my boat with plastic ones, so I don't have to worry about corrosion. My only concerns with this are the cocks in the engine bay. If there was a fire, would they melt? I presume so.

Can anybody point me to any articles/advice on this?

I think the heads cocks will be plastic so I don't have to run and earth all the way up the boat.
 
Nathan

it might be worth you having a look at Vyv Cox's site where he considers earthing and corrosion.

http://coxengineering.sharepoint.com/Pages/default.aspx


In several threads there is an opinion that sea cocks so not need linking in to the anti-corrosion circuitry.


The best plastic sea cocks are Marelon

http://www.forespar.com/what-is-marelon.shtml


On Sailnet, there is a discussion on Marelon vs Bronze

http://www.sailnet.com/forums/gear-maintenance/3549-marelon-vs-bronze.html



If you have a fire in the engine space, a melting sea cock will be the least of your worries, but I suppose you could always make up a heatresisting 'shield' out of Celotex FR foam to be sure. In fact, using Celotex for insulation on the renewal components of the UFO where appropriate might be worth considering.

http://www.celotex.co.uk/products
http://www.celotex.co.uk/products
 
nathanlee said:
I'm considering replacing all the seacocks on my boat with plastic ones, so I don't have to worry about corrosion. My only concerns with this are the cocks in the engine bay. If there was a fire, would they melt? I presume so.
Click to expand...

Don't forget your hull is made of plastic too! :)

Pete
 
Brilliantly useful and decisive replies folks, thank you.

Plastic it is.

If I can wangle a few long weekends off this spring, I might even get this floating palace in the water this summer.
 
Plastic seacocks are not accepted in the engine space by the MCA for coding purposes - read into that what you will.

Plastic seacocks come ino their own in metal (steel and aluminium) hulls. In GRP hulls they have no advantage for corrosion reasons over DZR.
 
Yes. Quite simple DZR is corrosion resistant and does not corrode in seawater.

This is not to say that all metals that look the same have the same properties. There is a vast amount published on the subject, but you need to read it to undrstand which materials are suitable and which are not. The recent issues on corrosion are because some manufacturers are not using DZR, which has been the material of choice for the last 30 years or so, but the RCD allows materials of a different spec which do corrode.

So choose DZR (or bronze if you have the money). Plastic of the correct type is equally good, but has no inherent superiority.
 
Tranona said:
In GRP hulls they have no advantage for corrosion reasons over DZR.
Click to expand...

truscott said:
Pardon?

Could you expand on that a bit for me please?
Click to expand...

In steel or aluminium hulls you have to be careful what other metals you attach to them, and how you do the attaching. In many cases, plastic insulating disks and sleeves are used to prevent any electrical connection between hull and seacock. If you get this wrong, hull and/or seacock will corrode. Using a plastic seacock makes the whole problem go away, which is why they have an advantage on metal hulls. On fibreglass hulls the problem doesn't exist in the first place, so no such advantage.

Pete
 
Ok. I understand what you were meaning now.

My issue has always been whether what I have is in fact corroding away, regardless of what my chandlery has said it's made of. Going with the TruDesign ones, takes away that niggle.

Ironically, the boat had Marelon fittings when we bought it, and the company that managed our refit convinced us that they were "plastic" and therefore unfit for purpose. They were removed and replaced with ones sourced locally in Marmaris. They very kindly painted all of the ball valves so I have no idea whether they are Bronze, Brass or some other combination that is happily wasting away. That was 4 years ago, so end of year refit is going to involve replacing those primarily for peace of mind.

PT.

Edit: Sorry PRV; I was aware of the issues, just wondered about Tranona's statement with regard to GRP.
 
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If you purchase your seacocks from a reputable source and specify DZR, these will be satisfactory in a GRP hul.

If the choice is between metal fittings of unknown provenance and Marelon then the answer is obvious. However, the latter are usually more expensive than DZR and are more bulky which may be an issue in some installations.

There are literally 10's of 000's of boats in use with DZR over the last 30 years or so which do not have a problem with corrosion.
 
The one downside I heard about the Marelon valves is that the handles can break off, and from what I heard, the handle is not a renewable item.
But thats just heresay from another forum, but may be worth while investigating
 
For what it's worth the seacocks on my 1973 Rasmus are original ,except for the engine intake. None ,except for the engine intake one,are bonded to the anode. Read into that what you will!

P'S She's out of the water at the moment and thney;ve all been subjected to the "THOR" test----bloody big hammer!
 
>with plastic ones

Marelon is not plastic, to quote the brochure 'Marelon is a proprietary formulation of polymer composite compounds using composite polymer resins and additives to produce a superior marine-grade product'. It's marine grade and meets ABYC (American Boat & Yacht Council) and ISO 9093-2 Standards. We have them on a steel boat.
 
KellysEye said:
>with plastic ones

Marelon is not plastic, to quote the brochure 'Marelon is a proprietary formulation of polymer composite compounds using composite polymer resins and additives to produce a superior marine-grade product'.
Click to expand...

That's a long-winded way of saying "plastic" :)

Pete
 
I've sort of acquired a guy who wants to look after my boat and his latest wheeze is to replace all the seacocks (12!) when the boat is next out of the water.

I've read a lot about how so many shatter if you attempt to remove them as they've become so fragile but have missed the examples and numbers of boats who have suffered as a result of ignoring the problem.

Given maybe 100,000 yachts afloat in Europe (too few??) do we have any idea what are the chances of anything going wrong with my boat in the next year - just so I can prioritise my risks and therefore my spending.

[My current top risk is fire after leaving kettle on and walking off to food shop as the impact would be very high and the likelihood quite high too, unless I make a conscious decision to replace wife after yesterday's incident.]
 
>The one downside I heard about the Marelon valves is that the handles can break off, and from what I heard, the handle is not a renewable item.
But thats just heresay from another forum, but may be worth while investigating

We know many metal boats with Marelon throughulls and I've never heard of handles breaking off. Given that they don't corrode and are immensely strong it highly unlikely if not impossible. Can you post the quote the other forum, I assume it gives a boat name and why it came to break?
 
KellysEye said:
>The one downside I heard about the Marelon valves is that the handles can break off, and from what I heard, the handle is not a renewable item.
But thats just heresay from another forum, but may be worth while investigating

We know many metal boats with Marelon throughulls and I've never heard of handles breaking off. Given that they don't corrode and are immensely strong it highly unlikely if not impossible. Can you post the quote the other forum, I assume it gives a boat name and why it came to break?
Click to expand...

No problem

Broken handles on Marelon valves, seems to be a few, but looks like its down to lack of lubrication/working/maintenance, brute force and ignorance, but once its broke, seems like a new valve is required

I just googled Marelon Handle Break, and these links are from the first page

http://www.cruisersforum.com/forums/f115/marelon-seacock-replacement-71984-2.html

http://lists.catalina320.com/pipermail/c320-list-catalina320.com/2011-June/035778.html

http://www.sailnet.com/forums/gear-maintenance/46847-broken-marelon-handle.html

http://www.ericsonyachts.org/infoexchange/showthread.php?6222-Lubricating-Marelon-valves
 
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