Advice on Anode please

[Billy Blue]

I had the boat lifted out yesterday after a year in the water and discovered that the single anode protecting the shaft & propellor had been completely eaten away, all that was left was the securing steel bar so it is presumably working well but I do not have sufficient protection. It was replaced last year. There is no damage to the propellor or shaft.
I am moored in the tidal part of the Medway on a pontoon and I do not keep power connected normally. The boat is semi displacement, single shaft.
The set up that I currently have has a anode on each trim tab and one on the side of the keel just forward of the propellor. The anode on the trim tabs are maybe 30% used after 2 years and I will replace them. The shaft/propellor anode is screwed into the side of the hull and then has a wire which runs from the anode to the fitting around the prop shaft where it comes out of the hull.
My knowledge of the science of how they work is somewhat small, well probably zero actually. So, I have some probably pretty basic questions which I would appreciate the answers to. I have already bought a replacement anode for the one that has been totally used up, I bought it before the boat came out of the water. So I was thinking of putting that one on and then supplementing it with a new larger one which I would secure by the more normal method of bolts through the hull.
(1) Is this sensible?
(2) What do I connect the new anode to? The engine block? Is there any particular type of wire I should use.
(3) Where should I place the new one? As near as possible to what it is protecting? It seems more sensible to put the new one on the transom rather than on the side of the hull (less impedance to the water).
(4) Do the anodes need to be linked at all?
(5) Or should I just scrap the original one and put one each side of the propellor on the transom.
I am sure you get the idea that I don't really know what I am doing so your advice would be much appreciated.

 

[bluejasper2]

hi billy there working ok you just have to change them every year i do,if they are not wearing away they are not working.

 

[carlton]

If it's eroding it's doing its job. Anodes tend to erode faster when fastened directly to the metal they're protecting.

I'd be tempted to stick two directly ON the shaft this time and monitor developments.

 

[VicS]

Anodes should be close to the items they are fitted to protect and "within line of sight" . The latter not to be taken too literally but they must not be shielded from what they are to protect.

There must be a good low resitance electrical connection between the anodes and the items they are protecting

Much useful information to be found on MG Duffs website

IIRC they recommend quite heavy gauge wire for connecting hull anodes.

If anodes are connected to the stern gear via a connection to the engine block/gearbox any flexible coupling in the shaft must be bridged.

MG Duffs "Electroeliminator" makes direct connection to a drive shaft.

I would not interconnect the anodes protecting the trim tabs with the one protecting the prop and shaft.

The statement, "The shaft/propellor anode is screwed into the side of the hull and then has a wire which runs from the anode to the fitting around the prop shaft where it comes out of the hull", makes me wonder if there is any connection to the prop shaft.