Hello Fellow Boaters…
This boating tip I thought I would talk about Sacrificial Anodes. Which are used to protect various metal components that make up the modern drive system. Below is a brief description of what function an anode performs.
An anode is attached to a metal object, such as a boat or underground tank, to inhibit the object’s corrosion. The anode is electrolytically decomposed while the object remains free of damage. Sacrificial protection is basically attaching a piece of metal that is more reactive that iron to the object made of iron. This more reactive metal, commonly magnesium or zinc, will corrode in the place of iron. That is, the more reactive metal will feed the iron with electrons each time the iron is oxidized to form iron ions, thus reverting it to iron once again instead of letting it become iron hydroxide (rust). Thus, the more reactive metal is sacrificed for the iron.
Problems:
-What are the purposes of using sacrificial anodes?
-How do sacrificial anodes function?
-What other forms of cathode protection?
-What different metals can be used as sacrificial anodes?
Answers:
-Sacrificial anodes are used to protect metal structures from corroding.
-Sacrificial anodes work by oxidizing quicker than the metal it is protecting, being consumed completely before the other metal reacts with the electrolytes.
-Several different forms of cathode protection are forming alloys, plating, and galvanizing the metal.
-Three metals that can be used as sacrificial anodes are: Zinc, Aluminum, and Magnesium.
Zinc: Preferably for saltwater however will offer some protection in freshwater.
Aluminum: For salt and brackish water.
Magnesium: For freshwater use only. Best option to protect drive systems in freshwater. But should not be used in salt water. (Most manufacturers install from the factory Zinc anodes since they will work to varying degrees in fresh or salt water. Since there is no way to know where the boat will be used.)
It is important to match the correct anode material to the area you will be boating in. In a freshwater application Magnesium is the best material to choose to install for out drive, shaft and rudder anodes. However it CAN NOT be used in salt or brackish water.
While there is vast amounts of data on the subject basically watching the condition of the anodes on you’re out drive or lower unit is a pretty easy task. They need to be tight and no more than ¼ – 3/8 eroded and clean of any bottom paint. If your boat is equipped with a Mercruiser Bravo 3 drive then it’s a good idea to make sure it is equipped with a additional prop shaft anode that provides extra corrosion protection. Mercruiser has a kit to enable a prop shaft anode to be installed if your out drive was not originally equipped with one.
Note: Make sure that the bottom paint is not touching the out drive transom plate or the aluminum hydraulic swim platform lift while leaving a 2″ gap is a normal practice in the marine industry.
Rick
Castaway Yacht Sales
