Grounding, bonding and lightning protection on a steel hull

[Julien de Tilly]

Hi everyone,

A friend of mine is seeking my help for finalizing the electrical installation on his boat before leaving for a 7-years trip around the world. The boat, for the most part, has been built from scratch by himself from an old Bruce Roberts steel hull that he acquired ten years ago. From what I know, he received a good deal of help from many friends, but many of these, among whom I place myself, weren't always specially qualified in boat building and engineering.

For my part, I only have the experience and knowledge that a total electrical refit on my own fibreglass sailboat gave me, which is, in my opinion, not that much. For that project, I read a lot (Calder, Cassey, Wing, ABYC regs, Maine Sail posts and website, etc.) to make sure I get appropriate and learned information on the topic. That be saying, and even if I'm proud to say that, too the best of my knowledge, I did a job up to the applicable standards, I'm obviously nothing even near of a certified marine electrician. And the knowledge I acquired during that project seems in my view to be only enough, in a somewhat socrative manner, to point out the vastity of my ignorance on the topic.

To be less lyrical, I came to think that if I simply apply the standards requirements the way they are stated, it is possible that they might pretty well cause a lot of undesirable side effects on a steel hull, potentially putting at risk the integrity of the boat itself, due to corrosion. Again, i'm not a physicist nor an engineer (in fact, I study philosophy), so my doubts may well be unfounded. And to be honest, it is more by what learned and trusted source stay silent upon than by what everybody else noisely jabbers upon that disturb me. Of course, I can ultimately refer my friend to some "certified marine electrician", but, from experience, these specimens seems to be pretty rare in my region - not to mention that some of the topics seems to a certain degree to be intrinsically controversial. So, as a first step, I would like to heard knowledgeable people with more experience than I have, to help us made our mind, and seek professional service if really needed (and available). If much of the wiring in itself doesn't pose a problem, i'm specially confuse by these topics:

A. DC grounding
1. Does a DC system should be kept on a floating ground on a steel hull?
2. If true, wouldn't the seawater inside the engine block/heat exchanger (a flexible coupling isolate the prop shaft) be enough to cause such a link to earth (the engine use a ground-return circuit) ?
3. If 1 and 2 are true, how corrosion should potentially be address and/or are they means to prevent unwanted ground to earth through the engine in normal circonstance (i.e. except while cranking)?
4. If grounding is a possibility, should the grounding point be the engine negative terminal, or on a dedicated submerged plate (which have to be isolated from the hull or not?), or directly on the hull (which is cover with an epoxy primer and antifouling paint).

B. AC grounding
1. If grounding DC circuit on a steel hull is a problem, how the issue of tying AC ground to DC negative be dealt with ? ABYC states that in an ungrounded DC system, AC ground must be connected to main DC grounding bus (and then to seawater). If that effectively provide a secondary path to ground for AC current in case of a fault, I don't see how it protects DC system (and people) from leaks in DC from a faulty charger or inverter (for exemple). Does using only marine rated equipment provide a sufficient degree of safety (isolated transformer), etc. Also, if I'm right, ABYC also ask to connect the chassis of such and equipment to DC negative bus as well, which seem contradictory to me here.

C. Bonding
1. The way I understand it, bonding is completely useless in any floating system, because there is no path in any case between earth (the seawater) and the negative side of the system (so leaking current will never try to reach battery terminal through thru-hulls, etc. ) If am I right here, it is however still questionnable if we could ever achieved a completely isolated system on a boat (an AC considerations here might be of some importance here)... But if grounded system is to be preferred even on a steel hull, should bonding be still avoided at any price, given corrosion problems ?
2. Related to that question : should the hull be grounded or bonded to something else (given tat it is coated on both side with epoxy primer and paint.)

D. Lightning protection
1. Should the hull itself be considered a good grounding point for lightning protection system, or should a dedicated plate be installed ? If so, does that plate needs to be elecritcaly isolated from the hull and/or linked to a sacrificial anode ?

Thanks a lot to everybody !

[Breaking Waves]

There are different perspectives on this.

There is the bond both ac and dc approach, the rational is well described here:

SmartGauge Electronics - To bond or not to bond - Hulls and electrical earthing

I think that would be the default approach without knowing more.


However, we personally had a “dc only” aluminum hull, which we designed to have a fully insulated/floating hull, with indicator meters to ensure it stayed floating.

[billknny]

Originally Posted by Julien de Tilly

Hi everyone,

A friend of mine is seeking my help for finalizing the electrical installation on his boat before leaving for a 7-years trip around the world. The boat, for the most part, has been built from scratch by himself from an old Bruce Roberts steel hull that he acquired ten years ago. From what I know, he received a good deal of help from many friends, but many of these, among whom I place myself, weren't always specially qualified in boat building and engineering.

For my part, I only have the experience and knowledge that a total electrical refit on my own fibreglass sailboat gave me, which is, in my opinion, not that much. For that project, I read a lot (Calder, Cassey, Wing, ABYC regs, Maine Sail posts and website, etc.) to make sure I get appropriate and learned information on the topic. That be saying, and even if I'm proud to say that, too the best of my knowledge, I did a job up to the applicable standards, I'm obviously nothing even near of a certified marine electrician. And the knowledge I acquired during that project seems in my view to be only enough, in a somewhat socrative manner, to point out the vastity of my ignorance on the topic.

To be less lyrical, I came to think that if I simply apply the standards requirements the way they are stated, it is possible that they might pretty well cause a lot of undesirable side effects on a steel hull, potentially putting at risk the integrity of the boat itself, due to corrosion. Again, i'm not a physicist nor an engineer (in fact, I study philosophy), so my doubts may well be unfounded. And to be honest, it is more by what learned and trusted source stay silent upon than by what everybody else noisely jabbers upon that disturb me. Of course, I can ultimately refer my friend to some "certified marine electrician", but, from experience, these specimens seems to be pretty rare in my region - not to mention that some of the topics seems to a certain degree to be intrinsically controversial. So, as a first step, I would like to heard knowledgeable people with more experience than I have, to help us made our mind, and seek professional service if really needed (and available). If much of the wiring in itself doesn't pose a problem, i'm specially confuse by these topics:

A. DC grounding
1. Does a DC system should be kept on a floating ground on a steel hull?
2. If true, wouldn't the seawater inside the engine block/heat exchanger (a flexible coupling isolate the prop shaft) be enough to cause such a link to earth (the engine use a ground-return circuit) ?
3. If 1 and 2 are true, how corrosion should potentially be address and/or are they means to prevent unwanted ground to earth through the engine in normal circonstance (i.e. except while cranking)?
4. If grounding is a possibility, should the grounding point be the engine negative terminal, or on a dedicated submerged plate (which have to be isolated from the hull or not?), or directly on the hull (which is cover with an epoxy primer and antifouling paint).

B. AC grounding
1. If grounding DC circuit on a steel hull is a problem, how the issue of tying AC ground to DC negative be dealt with ? ABYC states that in an ungrounded DC system, AC ground must be connected to main DC grounding bus (and then to seawater). If that effectively provide a secondary path to ground for AC current in case of a fault, I don't see how it protects DC system (and people) from leaks in DC from a faulty charger or inverter (for exemple). Does using only marine rated equipment provide a sufficient degree of safety (isolated transformer), etc. Also, if I'm right, ABYC also ask to connect the chassis of such and equipment to DC negative bus as well, which seem contradictory to me here.

C. Bonding
1. The way I understand it, bonding is completely useless in any floating system, because there is no path in any case between earth (the seawater) and the negative side of the system (so leaking current will never try to reach battery terminal through thru-hulls, etc. ) If am I right here, it is however still questionnable if we could ever achieved a completely isolated system on a boat (an AC considerations here might be of some importance here)... But if grounded system is to be preferred even on a steel hull, should bonding be still avoided at any price, given corrosion problems ?
2. Related to that question : should the hull be grounded or bonded to something else (given tat it is coated on both side with epoxy primer and paint.)

D. Lightning protection
1. Should the hull itself be considered a good grounding point for lightning protection system, or should a dedicated plate be installed ? If so, does that plate needs to be elecritcaly isolated from the hull and/or linked to a sacrificial anode ?

Thanks a lot to everybody !

I am going to pickup a couple of your questions... If you have a steel hull, lightening ground is really a non-issue. Your mast and rigging are surely already in good electrical contact with the hull, and nothing else is needed.

The BEST engine installations DO have the block isolated from battery negative return. These are not common (more parts to manufacture==higher cost), but are also not at all unheard of. Use an isolated negative alternator, and a relay that only connects the engine block to ground during cranking. There is a bit more to it, but that's the gist of the idea. My Volvo TMD22 has such an installation. A few VERY well made engines actually have a starter motor that has a dedicated negative return, but these are rare in normal marine conversions of general purpose blocks.

Your comment that "bonding is useless" in a floating ground system is 100% wrong. Bonding for corrosion control and battery negative return are completely different things, and CAN be done separately. Bonding ties all the underwater metal parts to a common zinc for corrosion control. This CAN successfully be done with no connections to the AC Safety ground system or the battery negative return system, but it take care and understanding to do so properly. There are many complications...

There are many way to do this, and there are well found and long lived boats that are done in different ways. The key is picking ONE system and sticking to it with religious fervor. Mixing and matching--even inadvertently-- different kinds of bonding/grounding/negative return systems will cause nothing but trouble.

[geoleo]

Originally Posted by Julien de Tilly

Hi everyone,

A friend of mine is seeking my help for finalizing the electrical installation on his boat before leaving for a 7-years trip around the world. The boat, for the most part, has been built from scratch by himself from an old Bruce Roberts steel hull that he acquired ten years ago. From what I know, he received a good deal of help from many friends, but many of these, among whom I place myself, weren't always specially qualified in boat building and engineering.

For my part, I only have the experience and knowledge that a total electrical refit on my own fibreglass sailboat gave me, which is, in my opinion, not that much. For that project, I read a lot (Calder, Cassey, Wing, ABYC regs, Maine Sail posts and website, etc.) to make sure I get appropriate and learned information on the topic. That be saying, and even if I'm proud to say that, too the best of my knowledge, I did a job up to the applicable standards, I'm obviously nothing even near of a certified marine electrician. And the knowledge I acquired during that project seems in my view to be only enough, in a somewhat socrative manner, to point out the vastity of my ignorance on the topic.

To be less lyrical, I came to think that if I simply apply the standards requirements the way they are stated, it is possible that they might pretty well cause a lot of undesirable side effects on a steel hull, potentially putting at risk the integrity of the boat itself, due to corrosion. Again, i'm not a physicist nor an engineer (in fact, I study philosophy), so my doubts may well be unfounded. And to be honest, it is more by what learned and trusted source stay silent upon than by what everybody else noisely jabbers upon that disturb me. Of course, I can ultimately refer my friend to some "certified marine electrician", but, from experience, these specimens seems to be pretty rare in my region - not to mention that some of the topics seems to a certain degree to be intrinsically controversial. So, as a first step, I would like to heard knowledgeable people with more experience than I have, to help us made our mind, and seek professional service if really needed (and available). If much of the wiring in itself doesn't pose a problem, i'm specially confuse by these topics:

A. DC grounding
1. Does a DC system should be kept on a floating ground on a steel hull?
2. If true, wouldn't the seawater inside the engine block/heat exchanger (a flexible coupling isolate the prop shaft) be enough to cause such a link to earth (the engine use a ground-return circuit) ?
3. If 1 and 2 are true, how corrosion should potentially be address and/or are they means to prevent unwanted ground to earth through the engine in normal circonstance (i.e. except while cranking)?
4. If grounding is a possibility, should the grounding point be the engine negative terminal, or on a dedicated submerged plate (which have to be isolated from the hull or not?), or directly on the hull (which is cover with an epoxy primer and antifouling paint).

B. AC grounding
1. If grounding DC circuit on a steel hull is a problem, how the issue of tying AC ground to DC negative be dealt with ? ABYC states that in an ungrounded DC system, AC ground must be connected to main DC grounding bus (and then to seawater). If that effectively provide a secondary path to ground for AC current in case of a fault, I don't see how it protects DC system (and people) from leaks in DC from a faulty charger or inverter (for exemple). Does using only marine rated equipment provide a sufficient degree of safety (isolated transformer), etc. Also, if I'm right, ABYC also ask to connect the chassis of such and equipment to DC negative bus as well, which seem contradictory to me here.

C. Bonding
1. The way I understand it, bonding is completely useless in any floating system, because there is no path in any case between earth (the seawater) and the negative side of the system (so leaking current will never try to reach battery terminal through thru-hulls, etc. ) If am I right here, it is however still questionnable if we could ever achieved a completely isolated system on a boat (an AC considerations here might be of some importance here)... But if grounded system is to be preferred even on a steel hull, should bonding be still avoided at any price, given corrosion problems ?
2. Related to that question : should the hull be grounded or bonded to something else (given tat it is coated on both side with epoxy primer and paint.)

D. Lightning protection
1. Should the hull itself be considered a good grounding point for lightning protection system, or should a dedicated plate be installed ? If so, does that plate needs to be elecritcaly isolated from the hull and/or linked to a sacrificial anode ?

Thanks a lot to everybody !

You are correct, your specialty is Philosophy.

[Julien de Tilly]

Thanks billknny ! For better understanding, let me follow up on some your answers as well:

Originally Posted by billknny

If you have a steel hull, lightening ground is really a non-issue. Your mast and rigging are surely already in good electrical contact with the hull, and nothing else is needed.

I agree that the rigging in itself will probably make a good path to earth. However, isn't it one of the purpose of lightning protection system also to try to "direct" the lightning current to maximize the safety on person on board by providing an insulated and low resistance path to ground ? Calder speaks in is book of the possibility, for exemple, on an arch forming, through the skipper, between the backstay and and binnacle/wheel/rudder assembly. Also, the mast base in itself is actually isolated from the hull via a rubber gasket to prevent corrosion. I perfectly understand that there is no miracle solution here, but wouldn't be better to stay on the safer path ?

Originally Posted by billknny

The BEST engine installations DO have the block isolated from battery negative return. These are not common (more parts to manufacture==higher cost), but are also not at all unheard of. Use an isolated negative alternator, and a relay that only connects the engine block to ground during cranking.

Yes, it was one of the options that we were already considering. However, I suppose that such an installation needs to have all of the gauge senders on the block be equipped with their own negative return as well to work while the engine runs ?

Originally Posted by billknny

Your comment that "bonding is useless" in a floating ground system is 100% wrong. Bonding for corrosion control and battery negative return are completely different things, and CAN be done separately. Bonding ties all the underwater metal parts to a common zinc for corrosion control.

I am not sure if I agree with you on that. For galvanic corrosion to occur, isn't an electrical connection between dissimilar metals parts in a same electrolyte (sea water) precisely required ? On fibreglass hull, for exemple, is it not true that electrically isolating each thru-hull from one another and other underwater metal parts considered a sufficient mean to prevent galvanic corrosion ? Tying them down to a sacrificial anode seems to me to be only required when a bonding system is also installed to prevent stray current corrosion that may be caused by some electrical fault, on a grounded system (leaking current from a worn bilge pump, to a seacock, to sea water, to propeller, to battery negative terminal). If the DC system isn't tie to earth, there wouldn't be in anyway a return path to the battery via sea water, hence no circuit ? It is certain that here, with a steel hull, all underwater metal parts are already electrically bond together via the hull itself, so zincs have already been placed to prevent galvanic corrosion. But if the DC system is kept floating, isn't true that stray corrosion form within the boat will never occur ?

Thanks again for the advice !