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DC Bonding questions

Feb 25, 2018
16
Sabre 30 None Long Island
Hi,

I suspect a stray voltage problem on my sailboat because I have seen the coating on my keel bubble off, exposing the lead in several places.

In tracking this down I am at the DC bonding system and I have read just about everything I can find on the subject. I refer to this link.
https://www.westmarine.com/WestAdvisor/Marine-Grounding-Systems

I isolated a problem to my VHF radio - the antenna has continuity with the mast, and therefore is bridging the DC bonding system from the mast to keel and also into the DC Battery negative. So potentially this could allow stray current into the DC bonding wires?

If I have a DC bonding system should it be connected to the engine negative AND the DC GND Buss bar OR just in ONE place at the DC GND Buss bar ?

How about if I follow recommendations to isolate my Spartan bronze seacocks and not bond, but to keep my lightning from mast to keel, should the lightning end there at the keel or have continuity to the DC GND Buss bar AND/OR engine to zinc ?

Thanks for any help on this
 
Mar 20, 2016
225
Beneteau 351 WYC Whitby
Buy a galvanic isolator ebay has the best prices ,I purchased mine from England for half the money they want here with a lifetime warranty.
 
Feb 25, 2018
16
Sabre 30 None Long Island
Hi Mechone, thanks for the follow up. Yes I purchased a Yandina 50Amp Galvanic Isolator and installed it into the incoming AC Green wire, and this AC Green Wire is then connected to the DC GND Buss bar.
https://yandina.com/GalvInfo.htm

I'm wondering if my actual DC bonding system is in order and according to the best practices.

Thanks
 
Last edited:
Jan 11, 2014
4,055
Sabre 362 113 Fair Haven, NY
If I have a DC bonding system should it be connected to the engine negative AND the DC GND Buss bar OR just in ONE place at the DC GND Buss bar ?
All three systems should only meet at one place on the engine block.

All the DC negatives should go to a bus bar and then to the engine block.

All the AC grounds should go to a bus bar and then to the engine block.
[Edit: The AC grounds should also be connected to the shore power ground with a galvanic isolator.]

All the bonding wires should go in series to the engine block. On the fittings, the bonding wires should only attach at one point, i.e., the fitting should be connected to the bonding wire, but not part of the bonding circuit. If there are 2 bonding wires attached to a fitting, the should attach at the same point so any stray current does not pass through the fitting.

Be aware that the Yandina GI is not a fail safe GI. If for some reason it fails, the AC ground will no longer be connected to the shore power ground. On a fail safe GI, if the GI fails, the AC ground remains connected to the shore power AC ground. The first option is better for the boat and stopping galvanic action, the second option is better for humans using AC electrical equipment.
 
Feb 25, 2018
16
Sabre 30 None Long Island
Hi Dave, Thanks for your reply. Noted about the Yandina being a non fail safe, that's a shame and I will look into a future better upgrade.

Just in case I'm not understanding - does this mean that the bonding system should connect directly to the engine block and not to to the DC negative buss, where the AC Green and Main DC GND connect ?

I'm confused about that, the actual physical connections to the engine block, which has continuity to the shaft zinc.

Urgh this diagram is showing 2 separate connections for the green bonding wire...another source of my confusion...
http://newboatbuilders.com/images/circuit8.jpg
 
Jan 22, 2008
7,032
Beneteau 323 Annapolis MD
Urgh this diagram is showing 2 separate connections for the green bonding wire...another source of my confusion...
The diagram looks decent. The engine is NOT a grounding buss, it is one of the things to be grounded to the -buss. You do not want to ground one wire on one side of the engine, then others on the other side. You do not want electricity to flow THROUGH the engine! Thus the "buss" block.
 
Jan 11, 2014
4,055
Sabre 362 113 Fair Haven, NY
Hi Dave, Thanks for your reply. Noted about the Yandina being a non fail safe, that's a shame and I will look into a future better upgrade.

Just in case I'm not understanding - does this mean that the bonding system should connect directly to the engine block and not to to the DC negative buss, where the AC Green and Main DC GND connect ?

I'm confused about that, the actual physical connections to the engine block, which has continuity to the shaft zinc.

Urgh this diagram is showing 2 separate connections for the green bonding wire...another source of my confusion...
http://newboatbuilders.com/images/circuit8.jpg
I see a couple of problems with that diagram, the most glaring is the connection of the AC green grounding wire with the AC white neutral wire. The neutral and the ground should not be connected on the boat, they are connected at the shore power panel.

The bonding system is not for lightening protection, it is to keep all underwater metals at the same electrical potential. The diagram shows the AC ground and the bonding system as one system, this will encourage galvanic corrosion.

How old is that diagram? Back when your Sabre 30 was built there was still some controversy on bonding and the AC ground system. I had some problems with my Sabre 30 that I wasn't able to resolve before I sold it.

Check the Yandina website for directions on how to test the Yandina GI. So long as the unit is tested periodically, it is OK to use the not fail safe GI. If you ever pop an AC circuit breaker, be sure to test the GI. I think there is more information on GIs on the MarineHowTo.Com website.

Also check Steve D'Anotonio's website for more information on bonding and GI.
 
Feb 25, 2018
16
Sabre 30 None Long Island
Thanks for the info Dave.

I have implemented some of the advice from the articles, and although not advised, I've completely separated my DC GND from the bonding and lightning systems.

1. GALVANIC - Removed bonding from all 7 of my Spartan bronze seacocks - interestingly they were bonded by the drain screws and also daisy chained, this would presumably encourage passing of voltage THROUGH the fittings... not anymore they are all totally detached from any wiring now. I was having to replace the outside fairing for the seacocks, and I wonder if the grounding was causing the fairing to separate, also the keel to shed faring...

2. GROUND FIX - Removed the Antenna connection from the rear of the VHF - thus removing the masts wrong alternate path to ground.

3. LIGHTNING MITIGATION - Replaced the bonding for mast and chainplates to one single place - a bolt on the keel (previously they dual connected to a port and starboard keelbolt)

The Zinc on the stainless prop shaft can protect the bronze Martec. For what it's worth, the zinc on the prop shaft has continuity to the engine.

If I make it to launch this season I will check the thru hulls with a silver half cell.
 
Jan 11, 2014
4,055
Sabre 362 113 Fair Haven, NY
I was having to replace the outside fairing for the seacocks, and I wonder if the grounding was causing the fairing to separate, also the keel to shed faring...
At least on the first 52 Sabre 30s, Sabre faired the through hulls and the strut with a polyester fairing compound. The trouble with polyester fairing is it shrinks. Over time the resin shrinks and eventually falls off. On the early 30s the through hull fittings were flared and not mushrooms with fairing over the top. The fairing compound lasted until it didn't.

In this image you can see the line where the fairing compound shrunk. This was taken as I was replacing the strut due to a crack in the strut. The crack followed the outline of the well into which the strut was bedded.
DSC_0066.jpg
d
 
Feb 25, 2018
16
Sabre 30 None Long Island
Wow interesting - I think you nailed it, the stuff I replaced was white, looked the same. Everyone in the yard was commenting 'why did Sabre recess the seacocks below the hull line like that'
It seems like such a bad idea that will invite rebedding at multi year intervals. I did not re-fair my strut yet.
The keel has areas of bare lead, I tried cleaning, and scrubbing epoxy into it with a new wire brush but it mostly bubbled off again last season. That's where I got my hunch about the stray current from..
 
Feb 25, 2018
16
Sabre 30 None Long Island
Also that cracked strut... wow. Firstly I can't imagine how that would even happen - maybe the yard replacing the cutlass bearing? Would be a horrible job to replace that on an S30. Would really need to take out the Diesel tank to get to the strut properly. Luckily the tank does just lift out of the port lazarette (I've replaced mine)
 

Maine Sail

Moderator
Feb 6, 1998
11,014
Canadian Sailcraft 36T Casco Bay, ME
Urgh this diagram is showing 2 separate connections for the green bonding wire...another source of my confusion...
http://newboatbuilders.com/images/circuit8.jpg
That diagram has a major flaw...

AC GREEN/GROUND/EARTH is never connected to AC WHITE/NEUTRAL on board the vessel unless you are unplugged from shore power and actively inverting, actively running a generator or you have an on-board isolation transformer.
 
Jan 11, 2014
4,055
Sabre 362 113 Fair Haven, NY
Also that cracked strut... wow. Firstly I can't imagine how that would even happen - maybe the yard replacing the cutlass bearing? Would be a horrible job to replace that on an S30. Would really need to take out the Diesel tank to get to the strut properly. Luckily the tank does just lift out of the port lazarette (I've replaced mine)
I'm not certain how the crack occurred, just glad I found it before launch.

No need to remove the fuel tank, the strut is aft of the tank. Crawl in to the sail locker and remove the side panels, its right there.
 
Jun 3, 2012
545
Hunter 33 Bay Pointe, Quincy
You can purchase a plastic antenna mounting bracket for your mast. This will keep the antenna shield isolated from the mast. I bought one years ago and it has held up fine despite my earlier misgivings about its robustness.