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Leroy
12-06-2004, 10:51 AM
Does anyone use zinc anodes on their boat? I think it is mostly for boats that stay in the water all the time and the water has a lot of electrical current in it for some reason. Or even an I/O that stays in the water?

Friend with larger boat said he is replacing his zincs every 2-3 months and he is at a fresh water marina with lots of other ski boats.

jimmer2880
12-06-2004, 01:00 PM
I thought you only needed zinks if you had aluminum in the water along with steel?


I grew up on the Potomac River (100% fresh water). We need Zincs for our I/O's & Outboards, but never saw an inboard with any problems. A couple inboards sit all season (they get really really slimy) without any zincs.

H20skeefreek
12-06-2004, 04:13 PM
this may or may not help

Copied from the West Marine website:

"Zincs"

Sacrificial Anodes and Galvanic Corrosion

Whenever your boat's hull is submerged in water-salt or fresh-there is the danger that various metal components will be eaten away by galvanic corrosion. This chemical reaction occurs when different metals are touching one another or are electrically joined together by a conductor in an electrically conductive fluid (an electrolyte). The least noble metals are referred to as active and are electrically positive in polarity, while the most noble metals are passive and electrically negative.

Sacrificial anodes can extend the life of your boat's hull, engine, rudder, propeller shaft, engine cooling system, refrigeration condenser and other components by protecting them from the deterioration caused by galvanic corrosion. When dissimilar metals are joined together in an electrolyte, the voltage or potential difference between the two causes formation of a galvanic cell in which one metal (the anode) will corrode while the other (the cathode) remains unharmed. Simply put, because anodes-usually zinc or aluminum-are made of a less noble metal than that of the parts they are designed to protect, they corrode instead of the components.

Galvanic self-corrosion can also occur in a single piece of hardware that's immersed in sea water and not in contact with a more noble metal. This happens when electric current flows internally, near the surface, between the bits of the less noble of an alloy's components, for instance zinc, and a nobler, copper component. Because it is less noble, the zinc can be eaten away, leaving a spongy copper residue. That is why it is so important to use marine-grade fasteners in underwater applications, so they are not destroyed, allowing a hose clamp to fail or your propeller to fall off. The higher the salinity and temperature of the water in which your boat floats, the greater the danger that corrosion will occur."

JimN
12-06-2004, 07:06 PM
The same principal works on water heaters. Gas and electric both have at least one anode, usually mounted in the top of the tank.

jimmer2880
12-07-2004, 07:05 AM
The same principal works on water heaters. Gas and electric both have at least one anode, usually mounted in the top of the tank.
and if you're on a well, and your water smells - if you remove the anode, the smell will probably also go away. A plumber friend of mine always removes it when he installs a water heater on a well system.

Back to my original answer.... Are we (comp boat owners on my stretch of river) just lucky? I'd love to know a good answer why our comp boats don't seem to be affected by electrolosis when I/O's & O's are.

H20skeefreek
12-07-2004, 08:27 AM
and if you're on a well, and your water smells - if you remove the anode, the smell will probably also go away. A plumber friend of mine always removes it when he installs a water heater on a well system.

Back to my original answer.... Are we (comp boat owners on my stretch of river) just lucky? I'd love to know a good answer why our comp boats don't seem to be affected by electrolosis when I/O's & O's are.


comp boat's have 2 kinds of metal under water. Stainless Steel and Bronze. If there is any galvanic corrosion that is going to happen it will be to the bronze, as SS is more noble than Bronze, but bronze is still pretty noble. You may notice some light pitting on your strut, but the electrolysis is probably seeking out something weaker, like your dock pilings or your neighbors boat (the I/O's).

Leroy
12-07-2004, 09:42 AM
Good info. I was worried about the nibral props since they are soft and in general softer metals are less noble. From practice never saw one "ate up".

DanC
12-07-2004, 12:29 PM
Jimmer, according to H2Os information there are two types of galvanic corrosion.

One is due to dissimilar metals. I/Os and O/Bs have all kinds of parts in the water (hose clamps, housings, gears, shafts...) so this is a primary concern. Inboards have very few parts in the water and they are usually all the same type of metal (expect the SS shaft). Since the rudder, prop/shaft, prop strut and fins are electrically isolated from each other, the only part you have to worry about here is the prop and shaft. Maybe that is why props occasionally get really stuck to the shaft? Don't know how you would put a sacrificial anode on a prop/shaft. The prop strut is electrically isolated by the rubber in the cutlass bearing.

The self-corrosion apparently only occurs significantly in salt water. I am guessing that the industry uses Nibral because it is noble and inert enough that you will shred your prop before you see significant self-corrosion.