Replacement anode problem

[zimbo]

I have today replaced the anode on my motor cruiser (moored and only used on the non-tidal Thames, so "freshwater").

On fitting it, there is a problem - see photo. The fixing brackets on the new anode are not flush with the bottom of the anode, whereas they were on the worn anode I removed. The new anode is a genuine MG Duff product.

The problem is that on tightening the nuts and getting the anode base flush and tight to the hull, there is a gap of about 5 mm between the underneath of each bracket and the hull (which is GRP).

This strikes me as a potential 'disaster' in waiting when sailing along: all sorts of debris could get caught in the forward gap (and maybe the rear somehow) and it would be impossible (I think) to be able to remove this when the boat is back in the water for the season (my boat is craned out of the river over winter).

I think I need to fill these gaps before craning back in to create a smooth profile so that nothing can get caught up whilst sailing.

Anyone had a similar problem and/or got any suggestions as to what I can use to achieve this? Obviously needs to be waterproof but I'm not sure what will permanently stick (and stay in place) on the metal brackets and the anti-fouled GRP hull.

 

[DavidJ]

Can you fit something more like this. Not necessarily this size but the shape

MGDUFF ZD58 Disc Shaped Zinc Boat Hull Anode (2.2kg)

 

[oldgit]

Leave it alone ...........nothing wrong with that anode or the gap.

If you want to be really fussy it is not unknown for folks to buy sheets of thin rubber and install between hull and anode.
Cut rubber to shape of anode after fitting.

 

[Bodach na mara]

The last Duff anode of that type which I bought came with a dense foam rubber mounting pad a spare nuts and spring washers.

 

[Plum]

The last Duff anode of that type which I bought came with a dense foam rubber mounting pad a spare nuts and spring washers.

That foam backing pad between the hull and the anode is really important. It stops wasting of the zinc from the underside of the anode. There is only a limited volume of zinc on the uderside of the slightly curved steel bar that projects out of each end. Once that zinc is lost the rest of the zinc falls off the steel bar leaving no protection. The next to go will be the zinc plating on your anode studs then the studs start corroding.......

 

[philipdawsonladds]

Most of the replacement anodes that I buy all come with the rubber backing gasket - easy enough to make one up though

 

[zimbo]

Thanks for the replies. I have visited the shop where I bought the anode and purchased a suitable backing gasket. Their view was that a gasket is not necessary, but it does no harm to fit one. I didn't argue but will err on the side of safety and fit it tomorrow.

 

[oldgit]

Thanks for the replies. I have visited the shop where I bought the anode and purchased a suitable backing gasket. Their view was that a gasket is not necessary, but it does no harm to fit one. I didn't argue but will err on the side of safety and fit it tomorrow.

The idea of the "gasket" is probably that of cushion so that the anode does not leave unsightly indentations in gelcoat ?
Usually only found on plastic boats,nobody bothers on working commercial steel boats.

 

[zimbo]

The idea of the "gasket" is probably that of cushion so that the anode does not leave unsightly indentations in gelcoat ?
Usually only found on plastic boats,nobody bothers on working commercial steel boats.

Don't know, I was more concerned by @Plum's post above. I have no reason to question him but I need to take the anode off again to replace one of the washers on one of the studs, so may as well fit a gasket. As my hull is GRP, your comment about not leaving a 'dent' also makes sense.

 

[Bodach na mara]

The replacement anode for the bow thruster came without the pad. Suggestions of what to use to make a pad would be welcome. It will need to be thinner than the sort of pad you find under a pear-shaped anode on the hull but slightly compressible to allow the flat-based anode to bed against the cylindrical tube of the tunnel.

 

[Plum]

The idea of the "gasket" is probably that of cushion so that the anode does not leave unsightly indentations in gelcoat ?
Usually only found on plastic boats,nobody bothers on working commercial steel boats.

See post #5

 

[Plum]

The replacement anode for the bow thruster came without the pad. Suggestions of what to use to make a pad would be welcome. It will need to be thinner than the sort of pad you find under a pear-shaped anode on the hull but slightly compressible to allow the flat-based anode to bed against the cylindrical tube of the tunnel.

Not all anodes need the foam pad. If the zinc can waste from under or behind the steel reinforcement that is within the anode then the front part of the zinc may fall away from that reinforcement. Worse, if the zinc behind wastes such that the tension on the studs is lost the anode will be loose with minimal electrical continuity to the studs so stops working. In these cases the pad behind prevents zinc lost behind. If the anode design is such that loss of zinc behind has no affect on the effectiveness then no pad required.

 

[Tranona]

The replacement anode for the bow thruster came without the pad. Suggestions of what to use to make a pad would be welcome. It will need to be thinner than the sort of pad you find under a pear-shaped anode on the hull but slightly compressible to allow the flat-based anode to bed against the cylindrical tube of the tunnel.

Never seen a pad on a bow thruster anode. The electric contact is made between the anode and what it is attached to. If you isolate it the anode will not work. As plum says it performs a specific function on a hull anode as the electrical contact with whatever it is protecting is via wire attached to the studs.

 

[Bodach na mara]

It's a plastic tube that goes through the hull from side to side. The anode is held on by two stainless setscrews which go into threaded holes in a metal strip on the "outside" of the tube, ie they are inside the hull.

 

[lydiamight]

An old discarded wet suit will provide you with enough material to make gaskets for a lifetime

 

[Tranona]

It's a plastic tube that goes through the hull from side to side. The anode is held on by two stainless setscrews which go into threaded holes in a metal strip on the "outside" of the tube, ie they are inside the hull.

Not sure I have seen an arrangement like that. On my thruster the anode is a button attached to the end of the drive shaft with a cap screw. What is the metal plate attached to/ and what is the anode protecting? The electrical contact will be through the screws to the plate and no need for a gasket.

 

[Bodach na mara]

As far as I know the screws go through the tube wall and tap into a plate on the other side. I confess that I have not looked to find out. I will check next time I am at the boat. I just assumed that it would be some part of the drive motor. I have no idea what is being protected as the propeller is plastic. It would not surprise me if nothing is being protected!

Not sure I have seen an arrangement like that. On my thruster the anode is a button attached to the end of the drive shaft with a cap screw. What is the metal plate attached to/ and what is the anode protecting? The electrical contact will be through the screws to the plate and no need for a gasket.

 

[Daydream believer]

Perhaps a fairing of Sticks Like. Or the equivalent waterproof version in Sika, whatever that may be.
A forumite will be along with the correct product to use, I am sure