Anode for rudder hinge

[john williams]

I wonder if anyone can help me with this-opinions would be most appreciated.
I have recently purchased a GRP hulled boat and have noted that there is a fair amount on corrosion on the rudder lower hinge plate. Nothing needs replacing yet but ill have to keep an eye on it.
The top hinge has an anode attached to it on the hull and seems in good shape. The bottom hinge is electrically separate and it looking the worse for it.
I want to attach an anode to the lower hinge and the obvious way to do this would be to withdraw one of the two through bolts and bolt on the anode using the vacant hole. I was going to use an anode bolt to keep the anode electrically connected to the hinge and the hinge bolted on to the rudder but then have begun to wonder if that would be strong enough. The anode bolts I have used in the past seem quite soft and the thread easily stripped.
If I were to drill a new hole in the hinge I'm worried I might weaken it. There dosnt seem a reasonable way to connect the lower hinge to the upper by the way. Any thoughts?
The boat is a 28 ft Morcombe bay prawner.
Thanks

 

[Tranona]

An anode may not do any good unless the the fittings are made of 2 dissimilar metals resulting in electrolysis. So best to investigate the materials first and if necessary change the fitting to say all bronze, all galvanised steel or all 316 stainless. Galvanised will of course eventually wear and rust and you need to be careful with stainless to avoid crevice corrosion by ensuring all bolts are well bedded in sealant.

If you do want to keep the mixed metals then you can attach the anode to the hull in the normal way and bond it with a wire internally to one of the fastenings for the fitting you want to protect.

 

[pampas]

I will assume you have a hull fitted anode earthed to the engine? If so link each pintel to the engine ( If no engine, connect to the hull anode) thus making them the same potential, should cure your problem

 

[Tranona]

An anode is not earthed to the engine, although it is commonly bonded to the bits it is protecting, usually prop and shaft using the gearbox as a path. Engines do not need any external anode. If they do have one it will be part of the engine in either the waterjacket or the heat exchanger.