Additional sacrificial anode for SO 42DS?

[andrewtas]

We’ve recently had Genevieve, our 42DS, out of the water for the first time in our ownership. Scrub, sand, anti foul and polish. You know the drill...

Whilst having a look underneath, I noticed some odd colouring on the shaft just forward of the prop. Scratching it with a screwdriver, we were horrified to see chunks of it come away. The collar anode was (obviously) just about gone and hence the shaft was being corroded. Fortunately, we were able to rescue it with repairs (replaced bushes and pins, filled holes) rather than having to replace the prop (nearly gave up when I saw the price for that!).

The motor vessel on the marina next to us had a sacrificial anode dangling over the side with an old power lead running back to the engine.

So - a comment and a question:

Comment - wow, the collar anodes are small. Check yours as there’s not much between you and a big repair bill...

Question - has anyone used the second anode to the engine solution? If so, how have you set it up? Or have you us d an alternate solution that you might share?

Thanks in advance.

[Charlie-Bravo]

Dangling an anode over the stern I have seen, and even considered doing it, however I believe the proximity of the anode to the mechanics you need to protect being greater than the existing shaft prop and hull anode ( some here have added another anode on the P bracket ... but mostly as the earth strap from bracket to ground is often broke) the Proximity of anodes is a real consideration, e.g. if you dangle it 50 feet away from your boat it will not have any noticeable effect, the closer it gets the better it will help.
Motor boats with equipment very close to the stern just might benefit from one a little.

I presume when you purchased, and surveyed , that the anodes were all newish, so they have been eaten in one year, and so you are wondering how you can improve the set up.

Having attached new anodes it is a good idea to meter each one to show a low ground resistance, next, the cable from. hull anode needs to be large and in good condition.
You may not have THE problem, marina stray currents , boats with dubiousness in their shore power set up close by, can lead to zincs disappearing faster than they should. 
Prop anode and shaft anode should last over a year, but I like to replace each season, hull anode I find they last 4 or more years , but I don't moor where you do.

last tip, place the shaft anode a good 2" away from the P bracket ( presuming not a saildrive) as the cutlass bearing lasts much longer if it gets a good flow of water to it.

CB