Yanmar Pleasure Boat Marine Engine Help

ZINC ANODES

I am of the opinion that more balderdash is talked about ' electrolysis ', than any other topic in boating!

I'll try and make the topic understandable. If I dont quite hit the mark, let me know. If there are some electrical boffins out there with big opinions, remember, I'm trying to keep it simple, not baffle the poor boatie with bullshit!
ELECTROLYSIS is the decomposition by electric current. ( Oxford Dictionary )
For electrolysis to occur there must be 2 things:
1. an electrolyte, in this case salt water.
2. Dis-similar metals ( we're only addressing the engine and power train here ) connected in some way, with both metals immersed in the electrolyte. The connection could be by a wire, life line, parts bolted together, etc.
Two dis-similar metals in an electrolyte will generate an electrical current flow which leaves the metal from the ANODE and travels to the CATHODE. As the electrons leave the anode they take the metal with them.
The anode is supposed to be eaten away, if it isnt there, the expensive aluminium or stainless or bronze parts will disappear instead ! For this reason it is called a ' sacrificial ' anode.
Pop up a GALVANIC TABLE that shows the relationship of dis-similar metals. I have abreviated it for relevance and simplicity.
This very abbreviated Galvanic Table lists metals in the order of their relative activity in sea water. The list begins with the more active (anodic) metal on the left and proceeds along to the least active (cathodic) metal of the galvanic series on the right.
Generally, the closer one metal is to another in the list, the more compatible they will be, i.e., the galvanic effects will be minimal. Conversely, the further one metal is from another, the greater the corrosion will be.

The area of the anode in contact with the salt water is critical, the smaller the area becomes, as it is working, the faster it will disappear. If you check your saildrive anode at 6 months and it's half gone it will be all gone before the 9 month period is reached. Replace it when it looks half gone. Genuine YANMAR anodes are the cheapest on the market ( unless someone is ripping you off ) and I strongly recommend you use them.
If a vessel is moored in an area with a reasonable tidal flow the anodes (saildrive leg, prop shaft, etc ) will be eaten away faster than if they were in slack water and must be checked more often.
Check out THIS PAGE for problems I have come across.

back to the top