Galvanic protection

Mark Bradley

Mark Bradley

Member
Jun 15, 2019
32
North Vancouver, British Columbia
Boat Info
240 Sundancer
Engines
5 LITER
Hi All

For what ever reason my aluminum anodes are not lasting too long. (Moored in saltwater.) Will hanging a larger Aluminum anode off the side of ones boat protect the outdrive the same as the anodes fasten to the leg? Cable of course will be bolted to engine block.

Thanks

Mark
 
Pure aluminum is usually for fresh water
Magnesium for brackish water
Zinc for saltwater

the aluminum in salt is going to be very active
 
Actually it's not pure aluminum, it's a formulated alloy. Most boats used in salt water now use this type. I thought the same until I started doing research on it.

Navalloy® Aluminum Anodes
The Only Anode That Works in All Types of Water

The aluminum alloy used in Navalloy anodes is very different from normal aluminum. It includes about 5% zinc and a trace of Indium, which prevents the build up of an oxide layer.

Aluminum anode alloy provides more protection and lasts longer than zinc. It will continue to work in freshwater and is safe for use in salt water. Aluminum is the only anode that is safe for all applications.



Thanks for the reply.......
 
I have never seen or heard magnesium being specified for brackish water, unless it is really close to fresh water salinity.
7382A4A1-424C-47F7-AD19-90AB6DD264A7.jpeg
 
Navalloy makes excellent anodes and the type you have is good.

How long is "not lasting too long"? Let's start with that.

Also... "moored" often refers to "out on a mooring all by itself". Or do you mean it's in a slip by other boats?
 
Sorry, actually met tied up to a slip in a marina.
We are getting a bit off topic, question was about hanging the same type of anode off the boat to take up some of the galvantic reactions taking place? ( save me from having to replace the Mercruser anodes so often)
 
Mark Bradley said:
Sorry, actually met tied up to a slip in a marina.
We are getting a bit off topic, question was about hanging the same type of anode off the boat to take up some of the galvantic reactions taking place? ( save me from having to replace the Mercruser anodes so often)
Click to expand...
In a marina? It could be the other boats around you.
 
Mark Bradley said:
Sorry, actually met tied up to a slip in a marina.
We are getting a bit off topic, question was about hanging the same type of anode off the boat to take up some of the galvantic reactions taking place? ( save me from having to replace the Mercruser anodes so often)
Click to expand...
No, we are not getting off topic. There was a very vaild reason I brought that up (along the lines of what Doc said). But again, how long is "not too long"?

Also... what drive do you have? And what do the anodes look like when you're changing them?
 
Last edited:
Mark Bradley said:
Sorry, actually met tied up to a slip in a marina.
We are getting a bit off topic, question was about hanging the same type of anode off the boat to take up some of the galvantic reactions taking place? ( save me from having to replace the Mercruser anodes so often)
Click to expand...

Actually to @Lazy Daze 's point, you could be dealing with stray currents from your boat, other boats or the dock itself. Leakage currents is a big deal in a marina and that could be the cause of your zincs being eaten up prematurely. Adding a larger anode will not really help your boat if any of those exists. In fact add a "guppy" over the side usually means the bonding system on your boat is failing is some way and the "guppy" is now the bonding plate.

But - https://www.boatzincs.com/hanging_anode_aluminum.html
Edit: Sorry didn't see @paulswagelock had already posted that link.
 
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