VP MD2020 and saildrive earth bonding

[broomstick123]

I have a Volvo MD2020 with an SD120 saildrive. The two parts are electrically isolated from one another as per the instruction book and the warning sticker on the bell housing. I had always thought that the leg is protected by the ring anode and my engine is connected to the hull anode. A friend with the identical boat and set up just had a VP engineer do some work on her boat. He fitted a new hull anode and through bolts and has bonded these to the bell housing, ie connected to the gearbox/saildrive. I've told her that I think that is very wrong, based on the instruction book and the warning label, but she has suggested that this engineer has said that this IS NOW the preferred way of bonding.
I don't want opinions as replies please. I want to hear from.anyone who can categorically confirm this advice.

 

[VicS]

The hull anode connected to the engine is serving no useful purpose.
A hull anode connected to the sail drive might offer some back up if the leg anode became completely consumed.

The saildrive leg is primarily protected by its protective coating. The anode protects the vulnerable area close to the prop shaft.

Some questions though. Does the boat have shore power? If it does is the earth connected to anything to provide a connection to the water (as required by the latest standards)? If so what?

 

[broomstick123]

The hull anode connected to the engine is serving no useful purpose.
A hull anode connected to the sail drive might offer some back up if the leg anode became completely consumed.

The saildrive leg is primarily protected by its protective coating. The anode protects the vulnerable area close to the prop shaft.

Some questions though. Does the boat have shore power? If it does is the earth connected to anything to provide a connection to the water (as required by the latest standards)? If so what?

 

[broomstick123]

The hull anode is connected to the engine block as a central ground/negative/ earth point. I would have thought that it would therefore offer protection to some of the dissimilar metals within the salt water areas of the engine. Raw water pump, heat exchanger and exhaust elbow.
Yes I hear what you say about the protective coating to the saildrive leg but are the waterways within the leg protected too. From having stripped a leg to change the hull seal I don't remember the internals having that protection.
The boat in question and mine both have shore power, but this is nothing to do with my original question. On my boat the shorepower earth goes to the hull anode and thus the block and the 12 volt negative but only having passed through a galvanic isolator on the shore power feed in.

 

[Tranona]

There is no need for a hull anode to the engine. It will do nothing because the water in the engine is not connected to the water that the anode is in! Volvo engines do not need anodes. Engines that do have pencil anodes screwed into either the block if they are raw water cooked or the heat exchanger if they are freshwater cooled (like my Beta). The anode has to be in the water with the dissimilar metals as it is the electrolyte that causes the galvanic action.

However if the hull anode is connected to the saildrive casing inside the boat it will provide some protection to the saildrive housing (just like a hanging anode that some people use) but in reality it is not necessary as the ring anode does that job and because it is actually on the housing will wear first before the remote hull anode comes into play. There is no need to ground the engine, although since 2011 it is a requirement to ground the shorepower circuit and some builders such as Bavaria do this with a button hull anode just as you describe in your last sentence - but it is nothing to do with protection from galvanic action on either the engine or drive.

 

[VicS]

The hull anode is connected to the engine block as a central ground/negative/ earth point. I would have thought that it would therefore offer protection to some of the dissimilar metals within the salt water areas of the engine. Raw water pump, heat exchanger and exhaust elbow.
Yes I hear what you say about the protective coating to the saildrive leg but are the waterways within the leg protected too. From having stripped a leg to change the hull seal I don't remember the internals having that protection.
The boat in question and mine both have shore power, but this is nothing to do with my original question. On my boat the shorepower earth goes to the hull anode and thus the block and the 12 volt negative but only having passed through a galvanic isolator on the shore power feed in.

+1 to every thing that Tranona says

Now that your friends hull anode has been bonded to the saildrive rather than to the engine there should be no other connections to it . , , , , In particular there must be no connection to the DC negative as this would effectively bridge the isolation between the engine and saildrive.

 

[Ammonite]

+1 to every thing that Tranona says

Now that your friends hull anode has been bonded to the saildrive rather than to the engine there should be no other connections to it . , , , , In particular there must be no connection to the DC negative as this would effectively bridge the isolation between the engine and saildrive.

Where would this leave other aspects of the original bonding system such as the connection to the rudder quadrant (stainless rudder stock with bronze heel fitting and copper rivets) and keel cooler for the fridge if applicable / fitted, which would be no longer connected to the anode?

Would it not be better to leave the original anode as is and add a secondary anode (if worried about the life of the saildrive anode) directly to the saildrive that is connected to nothing else?

 

[Tranona]

Where would this leave other aspects of the original bonding system such as the connection to the rudder quadrant (stainless rudder stock with bronze heel fitting) and keel cooler for the fridge if applicable / fitted, which would be no longer connected to the anode?

Would it not be better to leave the original anode as is and add a secondary anode (if worried about the life of the saildrive anode) directly to the saildrive that is connected to nothing else?

There is nothing in the original question of a "bonding system" nor of anything to do with the rudder or keel cooler. If a boat requires these items to be protected by an anode they should be done directly and probably individually as it is difficult to site one anode that will protect things so physically far apart. Bonding systems are not favoured now simply because most modern sailing boats don't need anything protected apart from the drive system - that is saildrive housings and propellers on shaft drives and these are dealt with individually. The need for anodes on modern steering gear is overrated as they rarely have dissimilar metals actually in seawater. Same with seacocks. There was a tendency at one point to festoon boats with anodes which sometimes caused more problems than they "solved" - because there was not a problem to solve in the first place.

These observations apply to GRP hulled boats. Obviously metal boats require a different approach. Wooden hulled boats are different again, but more akin to GRP in that generally they only need anodes for propellers, and many older boats don't even need that because they often have bronze shafts and proper bronze props - at least originally.

 

[Ammonite]

There is nothing in the original question of a "bonding system" nor of anything to do with the rudder or keel cooler. If a boat requires these items to be protected by an anode they should be done directly and probably individually as it is difficult to site one anode that will protect things so physically far apart. Bonding systems are not favoured now simply because most modern sailing boats don't need anything protected apart from the drive system - that is saildrive housings and propellers on shaft drives and these are dealt with individually. The need for anodes on modern steering gear is overrated as they rarely have dissimilar metals actually in seawater. Same with seacocks. There was a tendency at one point to festoon boats with anodes which sometimes caused more problems than they "solved" - because there was not a problem to solve in the first place.

These observations apply to GRP hulled boats. Obviously metal boats require a different approach. Wooden hulled boats are different again, but more akin to GRP in that generally they only need anodes for propellers, and many older boats don't even need that because they often have bronze shafts and proper bronze props - at least originally.

Thanks Tranona. It was more of a what if question, hence the "If applicable/ fitted" in case the original anode was connected to something other than the engine, which happens to apply in my case where the heel of the stainless rudder stock is bronze...and VicS comments about making sure the anode connected to the saildrive is not connected to anything else. My guess is that the VP engineer is probably not thinking about anything other than the saildrive and engine which might be fine, but potentially not, which is why I asked.

 

[Tranona]

I had a stainless rudder stock into bronze, but with a Delrin bearing. however if the shoe is proper bronze it should not be a problem with 316. The problem with modern props is that they are usually brass and it is the zinc that gets depleted when on a stainless shaft. an anode reduces that. On my last boat with a shaft I had no anode and no problems with a fixed prop, but when I fitted a feathering prop that had an anode because of the mix of metals in the prop rather than the prop and the shaft. Current boat has the same and no anode to the shaft. Will see if the prop anode is enough when I lift in a couple of months' time. The 2 blade folder on a saildrive on my Bavarias had no anode at all. No sign of any corrosion in the 10 years I had it.

 

[Ammonite]

I was forgetting about the delrin bearing that the rudder stock sits in. Do you know what the thinking was behind bonding the rudder in the first place? It's a late 90's Moody.

 

[Tranona]

That was the "bond everything" era when designers and builders were still getting their heads around galvanic action on new style boats with new combinations of materials. So covered themselves by adding anodes where in reality they were not needed. The subject is much better understood now and the approach now is to look at a situation from first principle. are the 2 dissimilar metals in contact in seawater; is there a big enough potential difference that might lead to a galvanic circuit. If yes fit an anode, if no don't. Your steering system does not pass the test. Sure there are dissimilar metals in the quadrant, stock, rams etc but none of these are in seawater as the seal on the stock keeps it out.

 

[Ammonite]

This is the current setup with the exception of the keel cooler for the fridge which has been subsequently added. What do you think should be left, altered or can safely be removed? There's also an additional belt and braces anode connected solely to the isolated saildrive for peace of mind after an electrical fault (now fixed) depleted the saildrive anode in 5 months. There isn't a galvanic isolator and the boat is not left plugged in. Apologies for the poor photo.

 

[Alex_Blackwood]

The hull anode is connected to the engine block as a central ground/negative/ earth point. I would have thought that it would therefore offer protection to some of the dissimilar metals within the salt water areas of the engine. Raw water pump, heat exchanger and exhaust elbow.
Yes I hear what you say about the protective coating to the saildrive leg but are the waterways within the leg protected too. From having stripped a leg to change the hull seal I don't remember the internals having that protection.
The boat in question and mine both have shore power, but this is nothing to do with my original question. On my boat the shorepower earth goes to the hull anode and thus the block and the 12 volt negative but only having passed through a galvanic isolator on the shore power feed in.

The hull anode that you refer to in the original post is your Earth connection for your electrical system , at least from your later description, nothing to do with protection for galvanic action. Do not confuse the two! The VP engineer has apparently, fitted an extra anode to to protect the sail drive. Nothing wrong with that.
Edit. Should have refered to Cathodic Protection. Not galvanic!,

 

[Tranona]

This is the current setup with the exception of the keel cooler for the fridge which has been subsequently added. What do you think should be left, altered or can safely be removed? There's also an additional belt and braces anode connected solely to the isolated saildrive for peace of mind after an electrical fault (now fixed) depleted the saildrive anode in 5 months. There isn't a galvanic isolator and the boat is not left plugged in. Apologies for the poor photo.

If I were uncharitable I would say that demonstrates a complete lack of understanding of the nature of galvanic action. What do they think that bonding the fuel tank, filter and filler to an external anode will achieve? I know they have problems with corrosion of fuel tanks, but that is because they use mild steel, and that there is a mix of metals (aluminium, brass and copper plus steel) in the system, but the key ingredient for galvanic action, an electrolyte is missing. So that can be removed. The engine makes some sense IF it is a shaft drive as that is the path to connect the anode to the prop, provided a bridge goes across a flexible coupling. However your boat has a saildrive so it does nothing because the engine is electrically isolated from the drive. While it might make some sense to attach it to the saildrive housing internally it really should not be necessary. the 240V circuit does not need grounding, but if you are doing it best to treat it independently with its own ground. I used a button anode direct from the CU after the galvanic isolator for mine as this was the way my Bavaria was done.

That just leaves the rudder and as I suggested earlier there may be some value in that, but I guess they did it because that is what they did on MOBOs where they used rudders that had stainless stock and bronze blades. Your rudder is a 316 stock and GRP blade. It is not clear where it is bonded to on the steering, but I guess the quadrant, but this is only a path to the stock as the quadrant is not in the water so does not matter what material it is made of. A slight proviso here is that this area of the boat can be damp so you could still get corrosion for example where stainless fastenings are used on aluminium tiller arms. Some lovely horror pictures on here recently of Beneteau MOBO tiller arms that have this problem.

My take on the subject.

 

[Ammonite]

If I were uncharitable I would say that demonstrates a complete lack of understanding of the nature of galvanic action. What do they think that bonding the fuel tank, filter and filler to an external anode will achieve? I know they have problems with corrosion of fuel tanks, but that is because they use mild steel, and that there is a mix of metals (aluminium, brass and copper plus steel) in the system, but the key ingredient for galvanic action, an electrolyte is missing. So that can be removed. The engine makes some sense IF it is a shaft drive as that is the path to connect the anode to the prop, provided a bridge goes across a flexible coupling. However your boat has a saildrive so it does nothing because the engine is electrically isolated from the drive. While it might make some sense to attach it to the saildrive housing internally it really should not be necessary. the 240V circuit does not need grounding, but if you are doing it best to treat it independently with its own ground. I used a button anode direct from the CU after the galvanic isolator for mine as this was the way my Bavaria was done.

That just leaves the rudder and as I suggested earlier there may be some value in that, but I guess they did it because that is what they did on MOBOs where they used rudders that had stainless stock and bronze blades. Your rudder is a 316 stock and GRP blade. It is not clear where it is bonded to on the steering, but I guess the quadrant, but this is only a path to the stock as the quadrant is not in the water so does not matter what material it is made of. A slight proviso here is that this area of the boat can be damp so you could still get corrosion for example where stainless fastenings are used on aluminium tiller arms. Some lovely horror pictures on here recently of Beneteau MOBO tiller arms that have this problem.

My take on the subject.

Thanks Tranona. Could the bonding of the tank, filler and filter be to comply with the US market as I think the US Coastguard do or did insist that all fuel systems are grounded regardless of whether they are petrol or diesel, even though diesel won't be ignited by a spark. So more to do with static rather than galvanic corrosion. Mind you the schematic is titled cathodic protection system. The tank is aluminium btw.

 

[Tranona]

Think you are right about the grounding rather than protection, but I don't think it is in the RCD and don't recall other boats of that era having it. However now most tanks, at least in production boats are plastic. not aware they used aluminium for tanks, all my experience of Moodys was looking at older ones almost all of which had rusty fuel tanks which were a PITA to remove!

Having slagged it off, TBH it does no harm leaving it all connected - just not doing anything useful. Would guess the hull anode lasts a long time.