Another bonding/grounding conundrum

[DLETF]

When my trawler was hauled for the first time since ownership recently, an area on the starboard hull around a Dynaplate showed corrosion. The area was about 1' x 2 ' with loss of bottom paint down to bare gelcoat in places. I have the following comments/questions:
1. There are 2 hull anodes; the Dynaplate on the starboard hull and an AL anode bolted to the hull near the stern. There is no SSB/HAM radio installed on the vessel. A galvanic isolator is installed on the vessel.
2. What is the cause of the hull corrosion around the Dynaplate?
3. Why is the Dynaplate being used for the bonding/grounding system when the stern anode could be used to bond/ground the entire vessel?
4. If the hull corrosion was caused by the bonding/grounding wires connected to the Dynaplate, should I remove those wires and connect them to the stern anode?
5. Pictures of the bonding/grounding system are attached to this post. Is there anything else wrong with the installation?
Thanks

 

[O C Diver]

What type of bottom paint? Is it high copper content?

Ted

 

[DLETF]

What type of bottom paint? Is it high copper content?

Ted

Interlude Micron CSC - cuprous oxide 37%

 

[kchace]

At least some of the thruhulls pictured use a hose clamp to clamp the bonding wire to the side of the thruhull. This never works for more than a short time if ever. Not only that, but the way the wires are captured under the hose clamps in 2 different locations WILL also add to the resistance. The bonding wires need to be connected to the same point at each junction. Since the whole thing appears to be daisy chained, as soon as you have high resistance at one point, everything else downstream will not be bonded. Check resistance from the main ground on your boat to each of the thruhulls and I bet you'll find high resistance. To operate properly, you need a MAX of 1 ohm between your main ground buss and every thru hull and zinc.

I would also check the galvanic isolator just to be sure its ok.

Ken

 

[sunchaser]

Following KC's excellent observations, I'd recommend a fresh start. Engage a well experienced marine electrician to properly redo the vessels bonding system. As well, go through the 110 systems and bring the ship's ground, individual grounds and neutrals up to ABYC recommendations and new GFCI code.

On your vessel this should not be a huge job provided reasonable access is available.

 

[Fletcher500]

At least some of the thruhulls pictured use a hose clamp to clamp the bonding wire to the side of the thruhull. This never works for more than a short time if ever. Not only that, but the way the wires are captured under the hose clamps in 2 different locations WILL also add to the resistance. The bonding wires need to be connected to the same point at each junction. Since the whole thing appears to be daisy chained, as soon as you have high resistance at one point, everything else downstream will not be bonded. Check resistance from the main ground on your boat to each of the thruhulls and I bet you'll find high resistance. To operate properly, you need a MAX of 1 ohm between your main ground buss and every thru hull and zinc.

I would also check the galvanic isolator just to be sure its ok.

Ken

OP, a question for the group, but I think it relates to your situation..

I assume daisy chaining is allowed per code, but a single wire to each thru hull is the better solution?

 

[rgano]

When I removed the SSB radio from my wooden hull, I left the sintered bronze ground plate in place and connected a heavy copper cable from my lightning rod to it, nothing else. The burning away of the paint around yours suggests some unwanted current flow. You might want to carefully hammer check you underwater through hulls while you are following the advice about checking resistances.

 

[gsholz]

The burning away of the bottom paint suggests you have a stray current problem vs a galvanic cell problem. The stray current could come from your boat or a neighbor boat or even a dock. If the corrosion rate is high, the stray current is likely DC. Check all your bilge pumps and switches for exposed positive DC wires and in general for any wires in the bilge.

If you are handy with a multi-meter you can measure voltage and resistance between your underwater metals. They should all be at the same potential.

 

[Comodave]

In looking at the photos it appears that there bare bonding wires that are clamped to the through hulls using hose clamps. That is certainly not recommended. If indeed you are to use hose clamps to connect a bonding wire to a through hull then a barrel connector should be installed on the end of the bonding wire not just bare wires under the clamp. Or you can drill the hose clamp and bolt a ring connector to the clamp.

 

[kchace]

OP, a question for the group, but I think it relates to your situation..

I assume daisy chaining is allowed per code, but a single wire to each thru hull is the better solution?

Daisy chain wiring is fine as long as the 2 wires are mounted to the same location. When you start putting wires on different points of the same item, you introduce multiple ways for increased resistance between the wires.

Ken

 

[Comodave]

OP, a question for the group, but I think it relates to your situation..

I assume daisy chaining is allowed per code, but a single wire to each thru hull is the better solution?

Yes daisy chaining is ok, but it is better to have a home run, so to speak, from each item. And it isn’t a code but rather recommendations.

 

[Duke of Patch]

I have a grounding conundrum - Grand Banks 36 trawler. . AC power is leaking though my engine DC neg ground to the prop shaft into the water. My AC power system seems good - however I found my AC green ground connected to the boats DC negative ground somehow- is this correct? DC and AC interface at the generator, frig and battery charger - is something wrong there. MY air cond. system is AC only (3 units) . I am getting serious corrosion on my bronze bow thruster and prop shaft anodes. It could be the marinas power has no earth ground and the neutral and ground are effectively one without earth ground at the panel? It could also be a live marina wire in the water looping through water to my boat ground - but seems unlikely.

 

[fgarriso]

You need to a Certified Marine Electrician to come out and check your grounding system, and AC system.

Someone could get electrocuted from stray currents !

 

[Comodave]

+1 on the certified marine electrician checking out the boat. You likely won’t electrocute someone but ESD, Electro Shock Drowning, is certainly a possibility, especially in freshwater.

 

[Comodave]

The AC ground and DC negative should be connected in the boat. But the AC neutral should not be connected to either of those. If you are not up on marine electrical work get a certified marine electrician, not a home electrician but a marine electrician. Electrical on a boat is different than a house. Don’t accept the yards guy that does electrical work, ask for one certified by ABYC standards.

 

[Duke of Patch]

stray currents

thanks for the tips - I am aware of the danger of electric shock drowning and a frightened the boat was in this condition for an entire season. I am 90% convinced the marina power has no earth grounding at the panel. I ran into this once in house wiring, lights would flicker and dim occasionally. I found the grounding rod wire in the panel was loosely connected to the neutral making the green grounding house wiring effectively partially live and sometimes fully live. I am still not convinced the green AC grounding system should be interconnected with the DC negative ground. I cannot see the purpose - I guess this is a question for a marine mechanic - again thanks - much appreciated.

 

[SteveK]

"When my trawler was hauled for the first time since ownership recently,"
What has changed if anything?
Pre purchase haul out did not see this and/or was the bottom newly painted? Was this plate bottom painted?

While daisy chain may be OK, what if the connection to the transom anode is lost and this dynaplate is now the in water sacrificial anode.

Also the bonding wire from dynaplate should be going direct to RF ground and/or your DC accessories' negative ground and not within the daisy chain circuit. IMO

 

[CharlieJ]

I hate it when somebody on a forum spouts their experience before posting but in this case I have to. I am a Certified ABYC Corrosion Tech with over 20 years in the field. I used to teach the ABYC Corrosion Certification course so I know a bit about the subject.

With that preamble, much of what is in this thread is wrong and/or dangerous if implemented. For instance; "daisy chaining" is specifically prohibited in the ABYC Standards; not dangerous, just wrong. And before the usual nay sayers jump in with "ABYC Standards are only voluntary." yes they are voluntary...but it is what insurance companies, surveyors and lawyers use so YMMV.

Regarding tying AC safety ground to DC ground, Nigel Calder has an excellent explanation on YouTube.

As for the rest of this thread, hire an experienced ABYC Corrosion Tech and have them perform a proper corrosion survey on the boat.

 

[twistedtree]

The AC ground and DC negative should be connected in the boat. But the AC neutral should not be connected to either of those. If you are not up on marine electrical work get a certified marine electrician, not a home electrician but a marine electrician. Electrical on a boat is different than a house. Don’t accept the yards guy that does electrical work, ask for one certified by ABYC standards.

The AC Neutral DOES need to be connected to the AC ground, but the "where" varies depending on the intended design. This "bonding" needs to happen and one, and only one location, typically at or near the power source. This gets complicated on a boat because the power source can and does move around. When plugged into shore power, the bonding point is always on shore in the land power distribution. This is probably what you are thinking about when you say it should not be bonded on the boat, and you are correct in this instance.


However if you have a generator, then when the generator is providing power, you need to bond on the boat. This is typically done right at the generator, and the power selector switch connects and disconnects the neutral as well as the power lines. So when the generator is selected, it's bonded neutral is used, and when the shore power is selected, it uses the on-shore bonding.


The same is true for inverters and inverter/chargers, and becomes even more complicated because sometimes the inverter is the only power source so need to have it's neutral bonded, yet other times there could also be shore or generator power operational in which case they would be providing the bonding. So Inverter bonding is often switched, either internally to the inverter, or externally.


And if your shore power runs through an isolation transformer, then a simplification is allowed where all the onboard neutrals are common, and there is a single ship-side bonding point, typically in the main electrical panel.


All this is in ABYC E-11 is you want to wade through it.

 

[twistedtree]

I hate it when somebody on a forum spouts their experience before posting but in this case I have to. I am a Certified ABYC Corrosion Tech with over 20 years in the field. I used to teach the ABYC Corrosion Certification course so I know a bit about the subject.

With that preamble, much of what is in this thread is wrong and/or dangerous if implemented. For instance; "daisy chaining" is specifically prohibited in the ABYC Standards; not dangerous, just wrong. And before the usual nay sayers jump in with "ABYC Standards are only voluntary." yes they are voluntary...but it is what insurance companies, surveyors and lawyers use so YMMV.

Regarding tying AC safety ground to DC ground, Nigel Calder has an excellent explanation on YouTube.

As for the rest of this thread, hire an experienced ABYC Corrosion Tech and have them perform a proper corrosion survey on the boat.

Listen to Charlie. He knows his stuff.


One thing I'll add is that if you have corrosion on the prop and other underwater metal, it's from DC leakage, not AC leakage.


Also, I see you have Picton listed as your location. If that's the NZ Picton, then everyone should note that we are talking about a 230V 50hz system, so some important details may be different vs North American power systems.


Regardless, all should be checked including dock power.

 

[twistedtree]

"When my trawler was hauled for the first time since ownership recently,"
What has changed if anything?
Pre purchase haul out did not see this and/or was the bottom newly painted? Was this plate bottom painted?

While daisy chain may be OK, what if the connection to the transom anode is lost and this dynaplate is now the in water sacrificial anode.

Also the bonding wire from dynaplate should be going direct to RF ground and/or your DC accessories' negative ground and not within the daisy chain circuit. IMO

Just a heads up that this is a new inquiry tacked onto a 4 year old thread.

 

[SteveK]

Just a heads up that this is a new inquiry tacked onto a 4 year old thread.

I hate when that occurs, now I have to read dates.

 

[CharlieJ]

#21:
Thanks Peter. I did not recognize that this was a vampire thread.

 

[BruceK]

Profile says OP is in Canada.
"About Duke of Patch
Vessel Name Duke of Patch Vessel Make/model Grand Banks 36 Classic City or Town Picton Zip or postal code K0K 2T0State/Province Ontario Country CANADA Home Port Waupoos"


Why does it matter so much it`s an old thread revived? The OP`s a new member who looks to have searched the archives,now labelled a vampire. Let`s be more welcoming.

 

[backinblue]

Sorry, but another learning opportunity for me. What is a vampire thread????

 

[Duke of Patch]

I am relatively new to this forum and am unaware of etiquette. I searched the archives for the most relevant posting and hoped that despite the stale date of the thread, some of the boaters with electrical systems experience might respond. I have come to realize that this is a complex question or more accurately a complex problem to solve as no solution is 100% safe and each solution has its downsides. In addition the subject becomes more complex with stray currents from nearby boats and faults in the marina power systems setup. A big topic..I wish to thank member Commodave for his suggestion to watch the youtube video by Nick Calder - very informative.

 

[Cigatoo]

I am relatively new to this forum and am unaware of etiquette. I searched the archives for the most relevant posting and hoped that despite the stale date of the thread, some of the boaters with electrical systems experience might respond. I have come to realize that this is a complex question or more accurately a complex problem to solve as no solution is 100% safe and each solution has its downsides. In addition the subject becomes more complex with stray currents from nearby boats and faults in the marina power systems setup. A big topic..I wish to thank member Commodave for his suggestion to watch the youtube video by Nick Calder - very informative.

Welcome to the forum. Happy to have another / fellow GB owner on board.

 

[twistedtree]

I am relatively new to this forum and am unaware of etiquette. I searched the archives for the most relevant posting and hoped that despite the stale date of the thread, some of the boaters with electrical systems experience might respond. I have come to realize that this is a complex question or more accurately a complex problem to solve as no solution is 100% safe and each solution has its downsides. In addition the subject becomes more complex with stray currents from nearby boats and faults in the marina power systems setup. A big topic..I wish to thank member Commodave for his suggestion to watch the youtube video by Nick Calder - very informative.

Your post is completely appropriate. I made the comment only because someone quoted the very first post which doesn't describe your situation. You have mostly received good answers to a good question.