Sea cocks

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olam

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What it the current thinking on sea cock/Though hull fittings replacement?
I'm about to lift the boat and replace some of the sea cocks,I am thinking of fitting bronze thru hull fittings & bronze sea cocks.
All fittings are unbonded.
Are all bronze fittings equal quality?
Presuming Bronze is better than DZR
 
DZR has equal corrosion resistance to bronze. Both materials are alloys of copper and tin plus other bits. I believe there are different grades of bronze but vyv cox is the man who knows.
 
ghostlymoron said:
DZR has equal corrosion resistance to bronze. Both materials are alloys of copper and tin plus other bits. I believe there are different grades of bronze but vyv cox is the man who knows.
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Not quite. DZR is dezincification resistant brass. Its composition is close to the 60/40 copper/zinc of 'ordinary' brass but with important small changes. The first is a tiny addition of arsenic, around 0.1% and the second is a very closely monitored composition that is not quite 60/40. The corrosion resistance is very similar to that of bronze, although bronze itself is not what it was due to steady reductions in tin content since the days when gunmetal held around 10% of it. BS-1400 LG2, probably the alloy used for seacocks, has only 5% of it, along with 5% of zinc that is there for deoxidation purposes. All of these also contain small amounts of lead that is there as a lubricant for forming and machining.
 
vyv_cox said:
Not quite. DZR is dezincification resistant brass. Its composition is close to the 60/40 copper/zinc of 'ordinary' brass but with important small changes. The first is a tiny addition of arsenic, around 0.1% and the second is a very closely monitored composition that is not quite 60/40. The corrosion resistance is very similar to that of bronze, although bronze itself is not what it was due to steady reductions in tin content since the days when gunmetal held around 10% of it. BS-1400 LG2, probably the alloy used for seacocks, has only 5% of it, along with 5% of zinc that is there for deoxidation purposes. All of these also contain small amounts of lead that is there as a lubricant for forming and machining.
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Is there any merit in using bronze/ gunmetal for the through hull skin fittings rather than DZR? Any significant difference in "strength" or other physical properties ?
 
So i guess the answer is 'not much in it'
That link makes interesting reading Mark.
Thought about Marelon but not quite convinced.
Will prob go for Bronze thru hull 7& DZR Valves.
Thanks for your replies.

Simon
 
I have to say that if I had a plastic boat I suspect I would go for a plastic through hull. It makes sense and removes a common electrickery fear that seems to pervade people's dreams.
 
pmagowan said:
I have to say that if I had a plastic boat I suspect I would go for a plastic through hull. It makes sense and removes a common electrickery fear that seems to pervade people's dreams.
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I've replaced all seacocks on our plastic boat but ended up doing Bronze and DZR. I would have liked to do plastic but the fittings are much larger than the bronze/DZR equivalent and I found that they wouldn't fit in the various confined spaces around the boat.
 
Kingfisher 3 said:
What about Marelon ... if you've got room to fit them?
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KellysEye said:
All our throughhulls were Marelon it's extremely hard, made of nylon and GRP and is the only throughull that can't corrode.
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Just to clarify, since Marelon seems in danger of becoming a generic:
Marelon is the registered brand name of a material described by Forespar as "a proprietary formulation of polymar composite compounds using composite reinforced polymer and additives". Forespar's web site claims it is comparable to bronze for abrasion resistance, tensile strength and flex modulus. I suspect, but can't be sure, that Marelon is exclusive to Forespar.

The other main maker of 'plastic' seacocks, Trudesign, describes its material as "glass reinforced nylon composite with high impact and tensile strength resulting in a light weight unit, free from corrosion and electrolysis issues." Trudesign do not use the word 'Marelon'; nor do they specify their material's properties to anything like the degree of Forespar with Marelon, although they do provide web links to a host of certifications.
 
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macd said:
Just to clarify, since Marelon seems in danger of becoming a generic:
Marelon is the registered brand name of a material described by Forespar as "a proprietary formulation of polymar composite compounds using composite reinforced polymer and additives". Forespar's web site claims it is comparable to bronze for abrasion resistance, tensile strength and flex modulus. I suspect, but can't be sure, that Marelon is exclusive to Forespar.

The other main maker of 'plastic' seacocks, Trudesign, describes its material as "glass reinforced nylon composite with high impact and tensile strength resulting in a light weight unit, free from corrosion and electrolysis issues." Trudesign do not use the word 'Marelon'; nor do they specify their material's properties to anything like the degree of Forespar with Marelon, although they do provide web links to a host of certifications.
Click to expand...

And Randex, mentioned above, is another plastic type, apparently using glass reinforced polypropylene.
 
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