Re: Replacement Anodes
Basically, an 'anode' is a sacrificial part of your boat. When you have two or more different metals that are connected physically and electrically (say for instance an aluminum prop on a SS shaft) you have imbalance of electrons...causing current to flow between the metals. This is accelerated greatly by being immersed in water, and even more drastically in sea (salt) water with more ionic content. As the electrons flow from one metal to the other, the remaining metal ions transfer to the water, depleting the physical construction of the metal -- also known as galvanic corrosion.
One of the easiest ways to prevent your precious boat components from corroding is to introduce another "sacrificial" metal to the mix -- preferably one who gives it's electrons up very freely, or at least more free than your precious metals. Common metals used for this is Zinc and Magnesium...the latter of which is more expensive but if you look at the periodic table, gives up electrons more freely than Zinc.
Anodes can be found in many places on boats as protection, but the most noticeable is the tab near the prop on the outdrive. If you find that the anode(s) on your boat is physically dissolving, this is good -- it's working. But also be wary to replace as it wears because when it depletes fully or falls off, this is when you will begin to see corrosion coming from your more precious metals. I've heard a good time to replace is when half the mass is gone.
