The PO of my boat painted over the zinc anodes on the saildrive. The anodes appear to be otherwise perfect. Can I sand/strip the paint off or do these need to be replaced?
Quick question about zinc anodes
- Thread starter Project_Mayhem
- Start date
Strip the paint. There's no reason to replace them. Make sure there is no paint on the prop under the zinc.
Make sure there is a good electrical connection between the anodes and the sail drive.
Freshwater anodes should be either aluminum or magnesium. https://www.boatzincs.com/engine-magnesium.html
Toss them. They are too cheap to risk your boat on something you don’t know the providence of. Read @Maine Sail article on zinc’s and tefgel at Marinehowto.com
I'm assuming perfect condition would mean that it has no electrical connection (paint, corrosion, etc) or the boat was never connected to dock power?
jssailem
SBO Weather and Forecasting Forum Jim & John
- Oct 22, 2014
- 22,356
Perfect condition for an anode is clean raw metal. Perfect attachment is secure to clean bare metal like your shaft. Best would be to have the boat out of the water where you can clean the shaft and assure that the anode matches the circumference of the shaft with a clean surface. That the anode is securely attached to the shaft.
That said, Near perfect is accomplished all the time when the correct diameter anode is matched to your shaft by a competent diver.
Saves the cost of hauling the boat.
That said, Near perfect is accomplished all the time when the correct diameter anode is matched to your shaft by a competent diver.
Saves the cost of hauling the boat.
If the boat has been in the water and the anode is in perfect condition, i.e., smooth dull gray metal, then the anode isn't working.
The proper name for an anode, is a sacrificial anode, with the operational word being sacrificial. The anode has little do with connection to shore power, it is there to prevent corrosion between the underwater metals in a boat (i.e., aluminum sail drives, through hull fittings, SS shafts, bronze props, etc.). When different metals are submerged in an electrolyte they form a battery. The idea behind the anode is to use a more reactive metal to provide the electrons in order to protect the less reactive and more important metals, like props, sail drives, etc.
Connecting to shore power without a galvanic isolator or an isolation transformer provides an electrical connection via the ground wire to every other boat on the same breaker panel (except those with GIs). This can accelerate the anode's sacrifice, but it is not necessary.
In the photo below are 3 anodes I have used. The first is a zinc anode that was on the boat when I bought it. The second is an aluminum anode after 1 season, the third a magnesium anode after 2 short seasons. The boat was in freshwater. Obviously the there was little sacrifice of the zinc anode, it wasn't doing its job.