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From: Arild Jensen (no email)
Date: Tue May 02 2006 - 20:03:59 EDT
> -----Original Message-----
> The short answer is: use military spec zincs and isolate the keel coolers.
REPLY
The Mil Spec Rob refers to"
the U.S. Government issued MIL Spec MIL-A-18001A in 1956 for the composition
of Zinc Anodes.
Further modifications eventually evolved into the present MIL-A-18001J
specification adhered to today.
The composition of metals and their limits are as follows:
Material MIL-A-18001J ASTM B418-80
Aluminum 0.10 - 0.50% 0.10 - 0.4%
Cadmium 0.025 - 0.15% 0.03 - 0.10%
Iron (maximum) 0.005% 0.005%
Lead (maximum) 0.006% -
Copper (maximum) 0.005% -
Silicon (maximum) 0.125% -
Zinc (pure) Remainder Remainder
( sorry for loss of format with ASCII text used for this post.)
Rob also mentions
> Any zincs may disappear due to water turbulance rather than galvanic
> corrosion protection
REPLY
The galvanic table in a real engineering text instead of the abbreviated
quickie consumer lists indicates that the millivolt levels are referenced to
a specific water flow velocity and temperature.
Galvanic action increases dramatically with both faster velocity and higher
temp.
All the more reason to completely isolate the heat exchanger from the rest
of the boat's bonding system.
In a closed circuit isolated from other influences youstand a better chance
of getting the intended life and performance. Copper alloys are prone to
corrosion when immersed with some other common marine metals.
regards
Arild
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