Drillhing hole in rudder to fit anode

[shoc]

I need to drill a hole in my rudder to fit an disc anode, what advice would you offer a total beginner?

see pic below of the rudder which is about 6-7mm thick

I know I need to buy the right type & size of bit, but what what else should I do regarding finishing of the rudder behind the disc anode? i.e. should I grind off the paint with a flat disk?

The boat is in fresh water, so looking at the current state of the rudder, should I remove the old paint and apply paint it with something new?

Cheers

 

[Norman_E]

If the rudder is steel an ordinary high speed steel drill bit will do the job. Start with a drill of about 4mm to make a pilot hole. Even a small battery drill will be enough if you increase the hole size in stages, but chock the rudder so that it cannot move, or you will probably break a drill. You must make sure that the new anode has good electrically conductive contact with the rudder, and rust is your enemy here. If you want to be absolutely certain of good contact at least grind off the paint where the anodes will sit, and repaint afterwards up to the edges of the anode. I assume you will buy disc anodes and put one each side, held by a single bolt. The steel will likely rust beneath the anodes and at each replacement you will have to clean up again.

Your picture shows a propeller with no anode and I think you need to attend to that first. You can buy special propeller nuts that take an anode on a tapered section. I am slightly puzzled as to why you need to fit anodes to the rudder as a well painted rudder is insulated from the water and should not suffer galvanic corrosion unless it is in contact with a more noble metal

 

[VicS]

I need to drill a hole in my rudder to fit an disc anode, what advice would you offer a total beginner?

see pic below of the rudder which is about 6-7mm thick

I know I need to buy the right type & size of bit, but what what else should I do regarding finishing of the rudder behind the disc anode? i.e. should I grind off the paint with a flat disk?

The boat is in fresh water, so looking at the current state of the rudder, should I remove the old paint and apply paint it with something new?

Cheers

If you want to protect both sides of the rudder you will need two anodes, one each side! A pair of button anodes can be fitted back to back

To be effective the anodes must make good electric contact with the rudder

An ordinary HSS drill bit will be suitable but you will need to drill a pilot hole and then enlarge this to the required size


If you are in fresh water then you need magnesium anodes but I would have thought that properly de-rusting, priming and a good paint system would be all that is needed.

 

[rogerthebodger]

I need to drill a hole in my rudder to fit an disc anode, what advice would you offer a total beginner?

see pic below of the rudder which is about 6-7mm thick

I know I need to buy the right type & size of bit, but what what else should I do regarding finishing of the rudder behind the disc anode? i.e. should I grind off the paint with a flat disk?

The boat is in fresh water, so looking at the current state of the rudder, should I remove the old paint and apply paint it with something new?

Cheers

I have a steel rudder and I welded stainless steel set screws on to fix my anodes on. No problem with contact resistance.

 

[VicS]

If the rudder is steel an ordinary high speed steel drill bit will do the job. Start with a drill of about 4mm to make a pilot hole. Even a small battery drill will be enough if you increase the hole size in stages, but chock the rudder so that it cannot move, or you will probably break a drill. You must make sure that the new anode has good electrically conductive contact with the rudder, and rust is your enemy here. If you want to be absolutely certain of good contact at least grind off the paint where the anodes will sit, and repaint afterwards up to the edges of the anode. I assume you will buy disc anodes and put one each side, held by a single bolt. The steel will likely rust beneath the anodes and at each replacement you will have to clean up again.

Your picture shows a propeller with no anode and I think you need to attend to that first. You can buy special propeller nuts that take an anode on a tapered section. I am slightly puzzled as to why you need to fit anodes to the rudder as a well painted rudder is insulated from the water and should not suffer galvanic corrosion unless it is in contact with a more noble metal

What evidence can you see that the propeller needs the protection of an anode ?

 

[Tranona]

Like others, can't see any need for an anode on a mild steel rudder. Anodes are used where there are two different metals in contact with eachother in (usually) seawater. Your setup is not like that so does not need an andoe - indeed you may well cause problems by fitting one as quite probably the plate is galvanised and you will break that cover by drilling.

As suggested the way to stop rust is to keep the rudder well painted. If you do have patches of rust then grind them off, coat with a rust converter such as Fertan and prime (Primocon is good) then antifoul.

 

[Norman_E]

What evidence can you see that the propeller needs the protection of an anode ?

It might well be the most noble piece of metal there and thus acting as cathode to the rudder but if the OP or other boats near him connect to shore power then an anode would be a very good idea. That Prop looks OK now as far as galvanic corrosion is concerned but I have seen plenty that have turned pink despite there being other metals of less noble character near them. I also know a case where a steel boat was moored next to yacht and the steel boat was connected to shore power and was putting current into the water. The yacht needed a new propeller because of corrosion after a winter afloat. With no anode on either prop or shaft its often the shaft that suffers most corrosion, and an anode on the shaft nut protects the shaft as well as the prop.

 

[VicS]

It might well be the most noble piece of metal there and thus acting as cathode to the rudder but if the OP or other boats near him connect to shore power then an anode would be a very good idea. That Prop looks OK now as far as galvanic corrosion is concerned but I have seen plenty that have turned pink despite there being other metals of less noble character near them. I also know a case where a steel boat was moored next to yacht and the steel boat was connected to shore power and was putting current into the water. The yacht needed a new propeller because of corrosion after a winter afloat. With no anode on either prop or shaft its often the shaft that suffers most corrosion, and an anode on the shaft nut protects the shaft as well as the prop.

You are making a good case for a galvanic isolator! Without if the situations you describe exist they will make short work of any anodes bonded to the shorepower earth

 

[Norman_E]

You are right about galvanic isolators, every boat connected to shore power should have one, but if the boat next to you does not anodes at least delay the onset of your underwater metalwork getting eaten.

 

[VicS]

You are right about galvanic isolators, every boat connected to shore power should have one, but if the boat next to you does not anodes at least delay the onset of your underwater metalwork getting eaten.

If you have your own GI in your shorepower connection that protects your anodes and other underwater metal work whether the boat next to you has one or not.
Its not only the boat next to you that can cause trouble, it's the steel piling etc around the marina that can be eating away at your anodes in you dont have a GI in your shorepower connection.


Not sure though whether all this talk of anodes and GIs is really relevant to a boat in fresh water or whether its a bit OTT.

 

[shoc]

Thanks for the advice so far, very helpful.

I wasn't too concerned about corrosion until the boat was lifted this year and the rudder appears to be quite pitted, some pics below.

In the marina there are lots of nearby boats connected to shore power so I've invested in a galvanic isolator and am fitting two weld on anodes (on the horizontal plate below the prop) and a rudder disc anode. Since the boat is kept in fresh water, it doesn't get lifted that often, about every 3-4 years so while its out now, I want to fit do whats required.




Here's a pic of the rudder in June-16, I don't know what the blue paint is but the 'broker' that I bought it from was quite 'dodgy' so could be cheap stuff to make it look good on the day.

 

[Tranona]

Really don't think an anode is going to help. That looks just like rust where the coating has failed. Same with an anode on the skeg if that is steel. I explained galvanic action earlier. It mostly affects yellow metals such as propellers when they are in physical contact with other metals such as a stainless shaft. If, however you electrically connect zinc to the yellow metal or the stainless it is attached to the zinc will erode in preference to the zinc in the yellow metal. There is no sign of that on your prop.

So your corrosion on the steel bits is likely just rust. The ultimate prevention is to take the rudder off, blast it and then galvanise before painting. The objective is to keep the water away from the steel.

 

[rogerthebodger]

If your boat is kept in freshwater I would grit blast back to bare metal then paint with at least 6 coats of epoxy tar. That's how the underside of my boat was treated.