Skin Fitting 316 vs Bronze

[Halo]

Dear All
I am changing my skin fittings and sea cocks over winter. Obviously I want to use the same material for all the parts to reduce risk of corrosion.
I want to use ball valve type seacocks for ease of operation and because of the space. I was going to use bronze but when I look at the detail on the spec the actual balls are chrome plated brass. I have never rated chrome plating for anything sea-going so that has made me think again. Also I have found a few hose tails, and bends in 316 in the back of the garage.
So the question is can anyone give advice on choosing 316 vs bronze (CB491K) for my application?
Many thanks
Martin

 

[haydude]

DZR (DeZincfication Resistant) Brass is almost as good as bronze, but not as expensive.

My boat still has chrome plated brass ball valves as fitted originally by the manufacturer (8 years in the water and still going strong). I have replaced one just yesterday with a DZR because of a leak from the ball handle shaft.

 

[prv]

Here's one of Kindred Spirit's stainless rudder bolts:

Admittedly this one was 304, but I replaced it with 316 and that was well on the way to the same state within a couple of years, when I replaced the whole lot with bronze.

No stainless seacocks for me.

Pete

 

[VicS]

Marelon!

 

[Bosun Higgs]

Prv has illustrated the problem with stainless - I hadanidentical experience with the skeg bolts on a prout cat and they weere 316. Avoid

 

[vyv_cox]

About a year ago I met the proprietor of C-spray, manufacturer of a big range of stainless steel fittings to many marine duties, not only leisure. Crevice corrosion is almost unavoidable, even in duplex which is far more expensive. The problem can be reduced by using sealants but in a valve I guess is going to be impossible.

 

[Tranona]

Balls are rarely a problem. The issues to do with seacocks are the materials used for the bodies and particularly the fittings. DZR valves and bronze or DZR fittings are fine in a GRP boat. Marelon is an alternative, but generally more expensive and may not be direct replacements.

 

[geem]

Prv has illustrated the problem with stainless - I hadanidentical experience with the skeg bolts on a prout cat and they weere 316. Avoid

We had a 1981 Snowgoose 37. I removed the skeg/rudder brackets when I first got the boat in 2002 to check them out prior to doing an Atlantic circuit in 2004/05. The s/s brackets had crevice corrosion but being farely beefy the brackets were not at risk. I did replace them as a precaution just to be safe. I had reason to remove the new ones a few time over the years to replace the top rudder bushes (due to the rudders floating and knocking) and everytime I removed the brackets they were perfect. I have no idea why the old one were a problem but it may have been down to the wrong spec of s/s. The new ones were 316L.

 

[Marsupial]

If you use duralac to seal a stainless valve onto a bronze skin fitting I don't think you will have any problems. I would be wary of using a stainless skin fitting because of the possibility of anerobic corrosion and crevice corrosion where the fitting passes through the hull.

The whole mixed metals and corrosion thing is a bit of a black science, sometimes the experiment is repeatable sometimes not, there are lots of Turkish boats in Turkey with stainless skin fittings and valves - haven't noticed any sinking - that's not to say I would "risk" it.

Years ago I was involved with an objective test of magnetic water treatment systems, we had three test houses all identical in every way and three sets of each device some were permanent magnets some were electromagnets. The devices worked in some and not in others, take a device that was not working in one and it would work in another, take a device that was working in one and it would work where the previous device didn't and the one that did wouldn't work in the other house etc. In the end we had to say that it may work and if it does there will be a benefit but then again it might not . . . . a bit lame but they were the findings.

The other thread on bonded skin fittings says it all, both approaches cannot be right - or can they? does it matter?