Yet another anode question!

[Thistle]

Following earlier advice in this forum, I'm fitting a plastic flexible coupling to my drive shaft. This will electrically isolate the shaft from the engine. Will I still need an anode on the shaft to protect the prop? Should I bond the shaft to the engine through the coupling?

Thanks in anticipation!

 

[tcm]

it would be better if the whole engine and drive shaft was plastic. But anyway, anything metal in the water needs an anode. Things not in the water and not cneccted to the water don't need bonding. However, to be on the safe side, perhaps bond all metal to the shaft, including the cutlery, and put small anodes on each knife and fork and spoon for when you do the washing up.

 

[Vara]

Empirical observation I had boat (Shipman 28) with hydraulic drive therefore no ground connection through shaft.Installed Decca Navigator and for once in my life followed instructions and earthed said machine through rudder post.All the loose electricity which had previously swilled about the bilge in an aimless and harmless fashion went straight to water and the rudder fell off.
Lesson take informed advice on this matter.

Historical note ."Decca navigator"Precursor to GPS had a quarter the capability and in real terms cost 10 times as much.

 

[macd]

What type of flexible coupling are you fitting? R&D, makers of what seems the most common type, also make a flexible 'bonding strip' so the shaft is not isolated from the engine. ASAP, amongst others, stock them. From memory, they're just a few quid.

 

[fireball]

I don't know _that_ much about all things anodey ... but ...

If your prop and shaft (and all metal bits connected) are of the same metal (or of the same nobility) then you won't need an anode - as long as you haven't got a hull anode one side and skin fitting bonded to it on the other....

However, if your boat eats anodes then I would put a shaft anode on it (still not connecting inside the boat though!)

Also - if you are in a marina you can get stray currents there - and that might cause problems too ... so I'd put a shaft anode on and keep an eye on it.

We just have a shaft anode on our current boat - and it isn't eaten away much...
We had no anode on the previous boat - and no problems at all ...
Both boats on swinging mooring - no shore power!!

 

[boatmike]

Very simply if the previous coupling was earthed through to the engine and you didn't have a problem then earth across the new one with an earthing strap too. In terms of anodes. Yes you still need one. A shaft anode is the best but if this is impossible fit one as near to the prop as possible and earth it to the engine. In this case the coupling strap is essential. With a shaft anode its still desirable to protect the engine which also suffers electrolysis through the seawater coolant. Don't forget your engine also has an internal anode too that requires attention periodically! Most yotties forget this one. Out of sight, out of mind......

 

[Thistle]

Many thanks. That was pretty much what I was expecting but I was just wondering if there was any reason I'd missed for not fitting one!