Ok guys... I stand corrected... I went to a noble metal table... Magnesium is at the top.. then aluminum... then zinc... then steel... So it would take the "less noble" metal to protect the underlying part.. So it is Magnesium anodes on the aluminum... aluminum anodes on the zinc parts... Zinc on the steel. But... the table also stated that in fresh water... there isn't electrolysis and and anode isn't needed. It also stated that there had to be a good electrical connection for the anode to work.

What they don't mention in the West Marine article is if you use aluminum to protect aluminum... they are the same material... so the sacrificial anode has to be bare and the protected aluminum has to be painted.

There is an article in BOAT US TRIALER CLUB Mag. this month about this very subject. Something is needed in both salt and fresh.

Brackish should be treated as salt.
Zink = Saltwater/Brackish
Aluminum or Magnesium = Fresh water.

Naturally, dont paint, wax or coat the anodes with anything and ensure a clean contact for maximum surface area.

Here is the noble metal table I found... you guys decide. My understanding is the Less noble metal protects the more noble metal. The article also went on to describe how quickly the electrons flowed... for comparison they move in speed somewhere between a snail and a growing vine...The snail being faster and the vine slower.... too funny.

[QUOTE=Reed Jensen]so the sacrificial anode has to be bare [/QUOTE

Yes, that much should be a given.

I have found that BOATFIX.COM has the best prices for the complete anode kits. $55 for the magnesium kit for B1's (pt# 888757a-1) and $47 for the B2 & B3. BTW, these are Mercury Marine/Quicksilver OEM
Kits include:
a)the 2 anodes for the trim cyls ends
b)large anode for front top of cavitation plate
c)anode behind the prop
d)round anode above the prop
e)All new screws

Just bought 2 complete sets of anodes at boaters world, and it says right on the package alum. I cant remember the co name but will check when I get home. Checked at west marine and there alum also. I'll check another source (merc) today. I would imagine alum to go pretty fast in salt and mag very expensive.

looked up merc parts for anodes and they only come in alum. or magnesium ? so which to use in brackish then ?

I would run the magnesium.. only because they provide the most protection.. you don't leave the boat sitting in the water for long periods do you? According to the chart.. you could use aluminum... But the rest of the aluminum parts must be properly coated or they will disolve as quickly as the anode.

Its definetly Magnesium for fresh water, especially if the boat stays in the water.

formula31 i leave the boat in brackish water for 2-3 weks at a time, so what should i use aluminum ?