Hello,

I have a 1987 Chris-Craft Stinger 260, with two mercruiser 260 engines, that are mounted on alpha one gen 1 drives. Acorn anodes on ONE engine are corroding excessively, in fact it looks they are "growing" with some porous action going on. All the other anodes are OK.
The electrics are partially new on the boat, meaning that its done over, does not look like spilled spaghettis everywhere. There is a new shore power solution with separate chargers for all the batteries, a proper mains switchbox and a galvanic isolator installed. There are battery switches, so that when off (boat at dock) only the battery charging and bilge pumps are connected. The pumps are new, and there is one connected to each engine battery. The engine electrics are connected by a common ground, but otherwise completely separated.
In addition to the engine batteries there is a house battery, and a bow thruster battery on board. They are also connected via ground, but separate otherwise (and off when docked).

How can it be that I have excessive decomposition on the acorns on ONE engine only in this case?

Any ideas?

Thanks in advance!
Ville

Maybe the quicker depleting ones are a lesser metal ? Ie: magnesium and other aluminium ?

Mercruiser/Quicksilver (and others) offer anodes in 3 metals.
magnesium , aluminium , and zinc.

Well can be. The boat drives in brackish water (Baltic Sea), and is stationed in a river inlet, meaning its mostly in a mixed fresh-brackish environment depending on the river current.
I believe the anodes I have are zinc in general. It is possible that these are different material. Hard to know... they look the same when bought .

I was suspecting an electrical anomaly, but it could be that they are of different material, magnesium for an example.

Thanks

I'll look at this from a different perspective , just for fun .
Maybe those anodes are the only ones that are grounded/bonded properly and the others (doing nothing) are the problem ?

That is a good point . But that would be almost impossible

When it comes to boats you can't rule anything out ! I once ran an Alpha 1 for about 20 years and the acorn anodes virtually never wore. The trim ram anodes and the zinc torque fin .. they were always active. On that particular unit what are the other anodes doing ?