A Random Bit of Knowledge: Zinc Fish

After living aboard for a little over a year and a half, we have learned that we need to have sacraficial zinc anodes hanging over the side of our boat to keep the electrolysis from erroding our propellor. Not only do you need the anode, you need to know which one to buy, and how to attach it to your boat properly.  
So what is electrolytic corrosion?

According to Defender: "What is Electrolytic Corrosion? If you've noticed corrosion on the metal parts of your boat located below the waterline, you are the victim of "galvanic corrosion". The scientific term "electrolytic" or "galvanic" corrosion describes the type of corrosion that anodes are intended to absorb. This corrosion is normally caused by different metals being near each other in salt water. Galvanic corrosion, an electromechanical action, causes metal parts to decompose. This destructive process is caused by electrolysis, an electric current set up between the metal parts of your boat, with salt water as the electrolyte. The effect is like a flashlight battery -- an electrical current is created and continues until one of the metals is eaten up -- the battery goes 'dead'." 

There are three types of sacraficial anodes, and you cannot use two different type anodes on the same vessel at the same time. The anodes are categorized by water type:
                Salt water: use a zinc alloy anode
                Salt water and brackish water: use an aluminum alloy anode
                Fresh water:use a magnesium alloy annode
These anodes need to be attached to a ground. 

We are currently living in a marina in salt/brackish waters where conditions for electrolysis are optimal, so--our sacrificial "zinc" will arrive in the mail next week.

More information can be found at: http://www.boatus.com/boattech/casey/sacrificial-zincs.asp