Unnecessary anode?

[mullet]

I'm scratching my head about whether my boat's hull anode is needed. Details:

• GRP boat on swinging mooring in saltwater
• Beta engine with pencil anode on raw water side of heat exchanger
• Flexible propshaft coupling; long keel so almost no prop shaft exposed to seawater
• Featherstrem prop with anode
• Bonding from engine block to hull anode

Is the hull anode actually protecting anything? It doesn't seem to have wasted at all last season (but the other anodes did, fast). I'm wondering if it is a hangover to the previous engine which was probably raw water cooled without a pencil anode.

 

[Pye_End]

If you have a flexible coupling your anode may well not be connected to anything in the sea. You may need to electrically bridge it. The one on the prop is probably doing the work (and is probably significantly more expensive). If you paint the prop then you may find significantly less anode loss.

 

[VicS]

I'm scratching my head about whether my boat's hull anode is needed. Details:

• GRP boat on swinging mooring in saltwater
• Beta engine with pencil anode on raw water side of heat exchanger
• Flexible propshaft coupling; long keel so almost no prop shaft exposed to seawater
• Featherstrem prop with anode
• Bonding from engine block to hull anode

Is the hull anode actually protecting anything? It doesn't seem to have wasted at all last season (but the other anodes did, fast). I'm wondering if it is a hangover to the previous engine which was probably raw water cooled without a pencil anode.

A hull anode has nothing to do with protecting an engine!

It has almost certainly been fitted to protect the prop .... If that is so the flexible coupling must be bridged to complete the electrical connection from anode to prop.

The Featherstream instructions say

About the anode
The propeller is protected from electrolysis by the zinc anode. This is designed to be used in addition to other anodes on the boat (hull, shaft anodes etc). If it is the only anode on the boat it is likely to be consumed quickly. The rate at which the anode is consumed varies enormously and it will be used at whatever rate it needs to in order to protect the propeller.

You should make sure your flexible coupling is bridged so that the hull anode can protect the prop

Alternatively a hull anode can be connected to the shaft immediately inboard of the stern gland using an "Electro eliminator " or similar arrangement

 

[[70521]]

You could remove it, but don't forget to plug the holes in the hull.

 

[Tranona]

at the moment it is doing nothing, but as already suggested it was probably intended to protect the prop from the shaft so the flexible coupling needs to be bridged to do that job. You are currently relying on the prop anode to ptotect both the mixed metals in the prop and the prop with the shaft -and it could be that is enough. However having an anode bonded to the shaft may reduce the rate of depletion of the prop anode. As it is there suggest you bridge the coupling and see what happens. BTW the shaft is totally immersed in seawater downstream of the inboard shaft seal.

 

[mullet]

Thanks, everyone, this has clarified things. Thinking about it, the prop anode didn't wasted that fast, it is the engine pencil anode that went really quickly. The prop anode wasn't new last season and there was still some left after 7 months in the water. But bridging the flexible coupling sounds sensible, I'll do that.

 

[Poey50]

I have an almost identical set-up having changed to a Featherstream, but in my case I know the hull anode does have electrical continuity to the shaft and propellor. I thought about removing the barely used hull anode but there are two reasons for keeping it. First, it provides some backup if, for any reason (e.g. illness) I can't get the boat hauled out at the end of a season. Secondly it acts as a grounding point for my AC system. I learned recently from Vyv Cox that it is possible to have too much anode protection which can show up in a reaction to the surface surrounding the anode, but in the absence of this I'm keeping it.