[Public-list] Electrolysis on Intake Thru-Hull

[Don Campbell]

Hi C.B.;
    I am in the process of replacing all my gate valves and through hulls and
have found that the alloys they call bronze are not at all constant. I don't
have a Chemical and Physical Handbook but am under the impression that brass
is supposed to be an alloy of copper and zinc and bronze is supposed to be
copper and tin. Since they are allloys , there is no easy non-destructive
test available.
    I took a through hull I had cut off the boat to the local scrap yard
where they had a gun that emmitted radioactive waves for metal detection and
it gave precentages to the 1/100 percentage. The old through hull was 82 %
copper, 4% tin and 6 % zinc. The scrap people called it red brass. It was
probably sold as bronze.
    I have since gone to the Conbraco and Perko  websites and Conbraco
suggest their bronze is 85-5-5-5. I have an e-mail awaiting reply from
Groco,  who don't reveal their bronze ratio easily to see if I match someone
else's THs with Groco seacocks if extra galvanic action will occur.
    The fact that your screen has gone pink is an indication it was brass and
that the zinc has been removed to leave only copper.
Don
#528


"C.B. Currier" wrote:

> Hi all,
>
> Well Infinity came out of the water yesterday for spring cleaning.
> During my cursory examination of the exterior I noticed 2 things:
> 1. The normal deterioriation of the zinc whas not as substantial as it
> normally is.
> 2. The new thru-hull water intake strainer I put on last year was
> pockmarked & looked quite rusty/pink & a little green.
>
> I had purchsed this striner from Bacons for a good price and thought
> nothing other than the fitting was bronze & should work fine in the
> capacity I was installing it for.
> I installed it and with caulk put a (Ball valve) shutoff valve on the end
> which is made of I think bronze & ss (stainless Steel). But I felt like I
> had isolated the intake striner fairley well.
>
> Looks like my isolation workd but the Galvanic current went for equally
> the Zinc and the strainer.
>
> Finally my question:
> I believe I should replace this (again) with a better quality / higher
> metal  strainer. What should I be looking for? BTW: I do not wish to wire
> this into  the motor thus sending what ever Galvanic current to the motor
> & thus to the zinc.
> --
> C.B. Currier
> Infinity #57
> Daybreak #458
>
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