Anodes - lack of wear and other stuff!

[MattK1969]

Hi. I have a 1989 Malo 116. She has a stainless prop shaft and a bronze(?) prop. No sign of an anode, do I need one? Also, the main hull anode, near the rudder has been painted over with copper coat and shows no sign of wear in two years. I assume I need to remove the copper coat, but how can I make sure that the anode is properly seated and conducting?? Any thoughts?
Matt

 

[Sandy]

If there is or is not an anode on the prop will depend on the make and model. Any evidence of an anode on the shaft? It is usual for the shaft to be connected via the engine block to the main hull anode.

Whoever copper coated the anode near the prop needs keel hauled. Remove that and replace it with a new one.

Lots of stuff on YouTube about how to measure if your anode is working.

 

[Tranona]

Back to basics. Anodes are needed where two metals with different potentials are in contact in seawater. The one with the lower potential can be protected by using a sacrificial anode (usually zinc) which has a lower potential than the metal you are trying to protect. The most common is stainless shaft and yellow metal propellers which often have a high zinc content and can dezincify. An anode can be introduced either direct on the propeller or shaft or attached to the hull close by and connected electrically to the shaft by a wire, usually through the gearbox housing.

It is quite possible that your propeller is a high quality "bronze" with low or even no zinc content and has a potential close to 316 stainless so does not need an anode. If there is no sign of dezincification (brittle edges to blades and pinkish spots) then no need to do anything. The anode on the hull is a different issue. It will not do anything if it is not bare zinc - but the key thing is to trace where it is wired to as that will tell you what it is trying to protect. It could be that it is wired to the gearbox and therefore to the shaft, assuming there is no flexible coupling, in which case it is probably not needed or it could be to the steering system. Again it is probably not needed unless the steering system and rudder have mixed metals underwater. Most don't.

 

[MattK1969]

Ok, that's a good answer, thanks.

 

[Caladh]

Hi. I have a 1989 Malo 116. She has a stainless prop shaft and a bronze(?) prop. No sign of an anode, do I need one? Also, the main hull anode, near the rudder has been painted over with copper coat and shows no sign of wear in two years. I assume I need to remove the copper coat, but how can I make sure that the anode is properly seated and conducting?? Any thoughts?
Matt

I think there should be an anode on the end of the prop nut. Fit a new hull anode and make sure it is grounded indide the boat. If you join our FB Malo Owners Group you will gain further knowledge !

 

[Tranona]

I think there should be an anode on the end of the prop nut. Fit a new hull anode and make sure it is grounded indide the boat. If you join our FB Malo Owners Group you will gain further knowledge !

No point in just fitting a hull anode and "grounding it" - to what? The anode has to be electrically bonded to the thing it is protecting, normally the propeller through the shaft. Often the gearbox fastening is used, but if there is a flexible coupling this needs to be bridged. a propeller nut anode is another way of protecting the prop and is usually sufficient and helpful if it is difficult to bond a hull anode. However many boats need no anodes at all. There is nothing special about anodic protection on a Malo - just follow the principles in deciding whether an anode is required and then use the most appropriate method of introducing one.

 

[Caladh]

No point in just fitting a hull anode and "grounding it" - to what? The anode has to be electrically bonded to the thing it is protecting, normally the propeller through the shaft. Often the gearbox fastening is used, but if there is a flexible coupling this needs to be bridged. a propeller nut anode is another way of protecting the prop and is usually sufficient and helpful if it is difficult to bond a hull anode. However many boats need no anodes at all. There is nothing special about anodic protection on a Malo - just follow the principles in deciding whether an anode is required and then use the most appropriate method of introducing one.

My hull anode is grounded (possibly my poor grammar or your interpretation) to the engine/g box - standard on our Malo’s.

 

[Tranona]

My hull anode is grounded (possibly my poor grammar or your interpretation) to the engine/g box - standard on our Malo’s.

That is not "grounded", but bonded to the prop shaft (via the gearbox and half coupling)t to complete the circuit to ,protect the propeller as I explained in post#3. Pretty standard procedure on shaft drive boats of all makes and types. As I suggested to the OP he needs to trace where the hull anode is bonded to as it will not be doing anything if it is covered with Coppercoat. It may well be to the gearbox, but if there is no sign of dezincification of the propeller, it may not be necessary at all. My 1979 boat has never had an anode and no sign of any corrosion.

 

[Caladh]

That is not "grounded", but bonded to the prop shaft (via the gearbox and half coupling)t to complete the circuit to ,protect the propeller as I explained in post#3. Pretty standard procedure on shaft drive boats of all makes and types. As I suggested to the OP he needs to trace where the hull anode is bonded to as it will not be doing anything if it is covered with Coppercoat. It may well be to the gearbox, but if there is no sign of dezincification of the propeller, it may not be necessary at all. My 1979 boat has never had an anode and no sign of any corrosion.

Sorry about the use of the word “grounded“. The Op was asking the Q and whether he understood bonded or grounded is open to debate. As an aside the hull anode is also bonded connected to a prop protector /electrical bush assembly as well, as most Malo’s have various types of aqua drive flexible coupling. Not sure about a Malo 116 Well done in not having any corrosion after so many years !

 

[Tranona]

Yes, that will avoid the break in continuity that a flexible coupling may introduce. Sounds like you have a Duff Electro eliminator in which case you probably don't need the connection to the gearbox.

There is a lot of misunderstanding about the use of anodes, Not helped by many builders in the past festooning boats with unnecessary anodes. Much better now at least with sailing boats.