Brass or bronze?

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Gwylan

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Have [ should] to replace through hull sea-cocks.
Especially the cockpit drains.

See a big difference in price.
So, brass & bronze?
Ball valve or gate?

What should I choose?
 
Gwylan said:
Have [ should] to replace through hull sea-cocks.
Especially the cockpit drains.

See a big difference in price.
So, brass & bronze?
Ball valve or gate?

What should I choose?
Click to expand...

Bronze or DZR brass, but not ordinary brass, your choice. Even Blakes seacocks are DZR these days and have been for quite a while

Ball valves seem to be preferred to gate valves.
 
prof pat pending said:
The first thing to consider is what else is on the bottom of your boat, some metals will work together, most won't
Click to expand...

I think that statement requires some explanation. What metals on the bottom would influence the choice between bronze and DZR and why.
 
The basic theory is that metals interact when in electrical contact with each other and immersed in an electrolyte (seawater). The more dissimilar the metals are on the anodic scale, the greater the speed of corrosion may be expected. This is why the norm is not to bond through hull fittings, so that they may not react with each other.

Brass is not a good material for underwater use as its composition allows the individual grains to react with each other and dezincification can be rapid, leaving a honeycomb of brittle copper. No material is entirely free of mechanisms through which they will degrade in an aggressive environment - DZR brass is much better than brass and a suitable bronze (not an inappropriately named brass!) better still. Bear in mind that sticking a stainless ball valve on a bronze thru-hull will accelerate corrosion in the bronze, though some have had great success, presumably because the sealant used on the threads has electrically insulated the two. Stainless thru-hulls are available, but some suspect that if imperfectly fitted the flange can be prone to crevice corrosion. Plastics don't suffer from galvanic corrosion, but are not everlasting and a prudent user will inspect on a regular basis (as you should with metal fittings) and replace when the colour density changes, which may indicate embrittlement.

On a friend's boat with bronze thru-hulls, the engine water inlet was so conveniently positioned that to promote free movement a domestic, brass gate valve was used - but recognising its potential weakness it was changed annualy at a price of around £1-50 (£20 for a bronze equivalent). Often the hose tails on a seacock assembly are brass and may eventually snap off when trying to remove the hose or if kicked. So long as the cock itself is of more suitable material at least you can then shut off the flow whilst you fit a replacement. If you plan to do any more than day sailing, it is a good idea to carry a few spares to make emergency repairs - cheap brass fittings will do for this, just dont forget to replace the bodge at the earliest opportunity.

Rob.
 
If it's the heads outlet I would also reccomend Forespar Marelon from ASAP.
I fitted one to my heads outlet.
No metals to eventually cause the valve to fail.
 
The alternative to Marelon ones from Forespar are the Tru Design glass reinforced nylon seacocks and through hulls and hose tails. I have them and am very pleased with them.
 
The 'plastic' option was not on my list, but is now in play.

In this case there is a need for a degree of confidence in the plastic versions.
Odd the relationship between the two apparent manufacturers.

The boat is GRP so it would rule out the electro-chemical issues. Even though the previous owner conscientiously bonded all the sea-cocks together.

More experience of plastic sea-cocks?
 
Gwylan said:
More experience of plastic sea-cocks?
Click to expand...

They have been used for many years in US and down under because DZR is not available there and bronze gets very expensive. So no worries about them. Tru Design are physically direct replacements for metal skin fittings/ball valve types, but some Marelon (Forespar) are not. Usually a bit more expensive than DZR.
 
I thought I would add that as I commented earlier , I fitted a Marelon seacock to my heads outlet.
However , I used a new DZR hull fitting and a DZR elbow either side of it and used Sika 291i to seal and adhese it all together.

As far as I can tell this works fine.

One issue I noted was that getting the retataining nut tight on the tail piece was very difficult in the tiny spaces you have to work in on boats.

I made a note to try and give it a final go at getting it tight enough the following day (it was not not loose it's just that you want to be sure) , however the 291i had cured and the whole assembly was absolutely secure.

Can't think as I write if 291i is a sealant or a sealant AND adhesive but it is reccomended for the job , as well as others of course.
 
TQA said:
My local US orientated supplier has ball valves described as ' marine brass' would this be DZR?

Also they have bronze ball valves for much the same prices.

Would you automatically choose bronze or is there reason to consider marine brass.
Click to expand...

I don't know 'marine brass' but it might well be DZR. For the same money I would have bronze but check that the ball and other parts are the same material as the body. In USA they probably are but in UK quite a few bronze bodies have brass balls and stems (stop sniggering at the back!)
 
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