How many shaft anodes?

[V12diablo]

I removed all my shaft anodes to clean all the growth that was on them and most were pretty well gone. There was 5 on each shaft, is that to many or should I replace them all. It’s a 2001 356 7.2 Mercruisers. The hull anode is in good shape.

Jason

[bud37]

Where will the boat end up....fresh water or salt ?

[buster53]

Some years ago, I read a thread on one of the boating forums regarding zincs. One guy, who really seemed to know his stuff, posted how it is possible to over-zinc a boat. 5 on each shaft seems pretty excessive to me.

Hopefully, someone knowledgeable will chime in.

[Midnightsun]

I must agree with Buster, mine came with 1 per shaft which is the norm I think. In fact, most boats I see on the hard do not even have any but I am in fresh water. Viper will know what is normal on the majority of boats. Would really help if you filled out a little more info in your profile, are you in salt or fresh?

[Viper]

Ya too many anodes is definitely a problem as it will cause another set of issues that you don't want. To say that 5 anodes on each shaft is overprotection though can be incorrect for that boat's particular set of circumstances. It could be that there was a stray current problem where the boat was moored before either from shore power or neighboring vessels, or a problem onboard. That many anodes seems excessive to me but I can't assess conditions of the water she's moored in or your onboard wiring. It can be as simple inadequate gage battery wires, corroded connections, poor bonding, etc. but it could be a marina issue or a neighbor. The only way to be sure is to have a pro on the subject take some measurements and go from there if the readings warrant it. Based on findings, they should be able to recommend the number of anodic protection you need.

The most anodes I've seen on each shaft is 2. IMO, if you need 5 per shaft, it's probably a Band-Aid for a problem that should be corrected. There's also the possibility that a previous owner figured he wouldn't have to hire a diver or get a haul out to change them as often if he just added more. This is a no no of course but we don't know if that was the reason or not. Usually one anode on each shaft and a transom anode are enough in a trouble free dock. You can try that then make observations throughout the season on anode and hardware corrosion (shafts, rudders, props, struts, etc.). If it looks like you need additional protection, you can add trim tab anodes, or rudder anodes. If after all that you still have a problem, you really need to determine why. If your anodes end up half their size in less than a season, it's usually a pretty good sign you're under protected by either not enough anodes or there is a problem causing them to give up their mass at an accelerated rate.

It's a complicated subject with an endless number of variables. No one answer suites everybody's set of conditions.

[km1125]

I definitely agree with the "five anodes is probably a Band-Aid for a problem that should be corrected."

I've only ever seen 1 per device (shaft, rudder, tab, etc). I might see a need for two if the shaft was VERY long or segmented but that would be pretty rare too.

I would also think that those extra four, especially if on both sides, would add a lot of drag to the running gear and eat up a few MPG at speed.

[tomschauer]

I run two aluminum anodes on each shaft and a 4 x 8" aluminum on the transom. They are good for three seasons in fresh and brackish water.

[bud37]

The reason I asked where the boat will end up ( salt or fresh ) is just this.....If going from salt to clean fresh, then you will have got zinc anodes on your boat now...the correct anodes are Magnesium so you will have to change all the anodes, the transom, any on trim tabs .rudders and shafts to Mag anodes. You should not have different metals in your anode package.

Now if the boat will end up in in salt going from salt, then zinc would be preferred, and I would replace all anyway cause clearly there may be a problem, zincs can get a coating rendering them ineffective ....they are cheap enough to go all new.....much cheaper than props/struts/rudders/thru hull fittings etc.

To add to all this, further investigation is necessary while the boat is on the hard, go about and test continuity from all the anodes to the boat ground to make sure they will be able to do their job efficiently.The transom divers dream should be checked also.This is the perfect time to inspect and clean all the bonding connections to engine ground and all the hull fittings, see if someone cut something.

Remember whatever situation you find yourself in, all the anodes should be matching materials.....good luck with your refit.

[Viper]

QR_BBPOST ....I would also think that those extra four, especially if on both sides, would add a lot of drag....

Totally agree km, not to mention that you can actually cause a wobble in the shafts which will likely become more pronounced as each anode wears at a different rate and causes an imbalance.

Sooo many things at play here, even how fast the water's current is plays a roll in how much protection you need.

[V12diablo]

QR_BBPOST Where will the boat end up....fresh water or salt ?

Fresh water,, Erie Canal and upstate NY lakes., it was in brackish water previously. I don’t mind replacing all of them, I do believe they are magnesium , is there a way to check? I planed on replacing them as I already removed the shaft anodes. I can definitely check the wiring and continuity on everything while it’s out.

Jason