Anode Best Practice on GRP hulls

[Swenns Dad]

Hi all.

New to the forum so assume this has been asked a dozen times, so links to previous advice welcome.

I have a Contessa 28. Reasonable amount of electronics aboard. Survey carried out prior to my ownership advised a teardrop anode should be installed, but without detail.

To this end I’m looking for ‘best practice’ advice.

Boat currently has stainless shaft with bronze prop, shaft anode fitted but seems to work loose.

She’s in saltwater harbour, chain mooring (no electric hook-up).

Bronze through hulls fitted, some have bonding leads on, some don’t.

Toe rail and other ally items have signs of electrolysis.... for info.

To this end, any advice in the following appreciated.

1. Best anode to fit.
2. Where to fit
3. Where and what should be bonded
3. Anything else you think may be useful.

 

[pvb]

The through-hulls don't need bonding. You could bond an anode to the engine block; as long as there's continuity to the prop shaft this will help protect the shaft. You could also bond to the rudder stock. The anode ought to be near the stern of the boat, fairly close to the centreline.

 

[Swenns Dad]

The through-hulls don't need bonding. You could bond an anode to the engine block; as long as there's continuity to the prop shaft this will help protect the shaft. You could also bond to the rudder stock. The anode ought to be near the stern of the boat, fairly close to the centreline.

That’s interesting re, bonding of the thru hulls.... as some are and some are not?

 

[doug748]

That’s interesting re, bonding of the thru hulls.... as some are and some are not?

Similar size and vintage of boat; none of my Blakes through hulls are bonded and have not been a problem so far. I have a single pear anode connected to the engine, this was the set up from new. The anode is often crusted over but it does seem to work but very slowly and unevenly, I moor in a mix of marinas and swinging moorings.

I think your toe rail corrosion may be an unconnected random event, I have four alloy cockpit jammers which have dissolved for no obvious reason

 

[De.windhoos]

put some locktide on the bolts in your shaft anode and if possible put 1 in from left to right and 1 from right to left.
I actually always have 2 anodes, just in case 1 drops off for some reason. It's overkill, but anodes are cheap and it beats putting one on underwater

 

[neil1967]

Remember that the anode should be in 'line of sight' of the object it is supposed to be protecting (in your case the prop).

 

[VicS]

That’s interesting re, bonding of the thru hulls.... as some are and some are not?

Through hulls and seacocks should be made of corrosion resistant material . ( bronze/ gunmetal, DZR brass , or plastic) and will not therefore need the protection of an anode.

I would feel inclined to remove the existing bonding .... if you do not have a hull anode at present just what are they bonded to ?

If you have no problem with corrosion of the prop you need do no more than maintain the shaft anode. If you have a decent manganese bronze prop you may not even need the shaft anode.

When fitting a shaft anode either whack both halves simultaneously with a good sized hammer in each hand or hold something heavy behind one half while whacking the other in order to bed the anodes onto the shaft. Then re-tighten the bolts using some loctite as suggested.

If you fit a hull anode ( see MGDuff's website for instructions.) it must be "able to see" the prop and be reasonably close to it. There must also be a good electrical circuit connecting it to the prop which will mean bridging any flexible shaft coupling or employing some kind of brush system such as MGDuff's "Electro- eliminator"