Grounding system on 1993 H375 Legend

[JamesG161]

When you talk about "avoiding it" Nigel, talks about creating a "zone of protection" and how to do that (see attachment). It was in reference to this concept that I asked about connecting the mast to the keel bolts, and if they would provide grounding the necessary ground to water...if they had a direct path to create the zone of protection. Please, bear in mind that Nigel is NOT talking about carrying lighting voltages THRU the mast to the water....

Nigel is well versed in lightning avoidance. The zone of protection is real and needs your stays and mast grounded. That zone is called a Faraday Cage. Deep or shallow water grounding, may have a point, but any grounding is better than NONE.

This rule - connect AC safety green to DC negative - is to keep people safe from an AC shock hazard on the boat. This has nothing to do with galvanic or stray current corrosion issues.

True with one exception, you don't have a galvanic isolator on the AC green and some idiot sends a DC current down the shore power on the AC green.
Jim...

 

[Charles Erwin]

True with one exception, you don't have a galvanic isolator on the AC green and some idiot sends a DC current down the shore power on the AC green.
Jim...

Jim

DC presents no shock threat. As to corrosion -- won't matter because galvanic isolator will not trap DC potential > 1.5 vdc,

Charles

 

[JamesG161]

DC presents no shock threat. As to corrosion -- won't matter because galvanic isolator will not trap DC potential > 1.5 vdc,

Don't tell me that! Really?
I thought the isolator was 2 isolated transformers, thus passing AC and not DC. I am going to check mine this week end.
Thanks
Jim...

 

[Charles Erwin]

Jim

No transformer stuff involved in a plain vanilla galvanic isolator.

Maybe you have isolation transformer installed that provides true (100% ) AC isolation. If so - a very different animal than we are talking about here

Charles

 

[Maine Sail]

Don't tell me that! Really?
I thought the isolator was 2 isolated transformers, thus passing AC and not DC. I am going to check mine this week end.
Thanks
Jim...

A galvanic isolator is nothing more than diodes that block galvanic corrosion but will not block stray DC corrosion. An isolation transformer electrically isolates your boat from shore AC and DC on the green wire..

IMHO every boat that plugs into shore power should be equipped with a true isolation transformer or simply not plug in... A galvanic isolator is a Band-Aid at best..

 

[Lander]

Thank You Everyone! You guys are great! Now, I have one more question about a common ground. As you may remember from the text above, the keel bolts are not part of the current carrying negative dc, but they are connected to the engine block (via water or..?) Nigel Calder discusses the concept of the common ground and illustrates it with a diagram in his book, which I have attached, rather than try to explain. So, my questions are:

1. whether the keel bolts are a de-facto common ground, and
2. whether using them as such is good or bad idea?

 

[Charles Erwin]

Questions
1. whether the keel bolts are a de-facto common ground, and
2. whether using them as such is good or bad idea?

We are not on your boat so we are accepting the results of those tests you have so far reported

Moreover, semantics are obviously a problem here. For example, it is impossible to understand why you continue to characterize how any three #10 wire keel bolt connections to 'something' could possibly represent any benefit under any conceivable circumstances (no matter whether these three are facto or de-facto) . To the point - how could such a connection possibly be a part of "a common ground" and what difference would it make if it were part of "a ground" whether common or uncommon? Even more confusing your question how "it" could be a good or bad idea.

You really cannot expect anything more than what has already been said in this discussion.

If you are actually serious about these questions - get somebody one who knows the score to go through this stuff with you, in person, with you present , on your own boat.

Do not take my comments as criticism. To the contrary there is nothing better - for any of us no matter how much we may have learned - than to go through this kind of thing in the field with someone else who has spent time and treasure to study these questions.

Charles

 

[JamesG161]

An isolation transformer electrically isolates your boat from shore AC and DC on the green wire..

That is what I understood.
I found about 5 VDC on my marina green wire that doesn't appear to entering my boat's green wire, but if the boats nearby don't have that "Band Aid", I can still have that stray DC come through the keel.

A new boat, three slips down, had just rewired their boat with a landlubber electrician. Before we knew what happened, had 2 burnt power cords, I lost 2 Hunter intermediate internal power breaker that were in the lazarette next to the inlet plugs, and smoked one shore power receptacle (much more happened to others). The only good news was my Hunter panel shore power breakers protected my main system. I also lost my zincs in 4 days from their stray currents.

Sounds like I need to patent a 15,000 volt Diode to prevent stray Currents from using my boat/keel as a DC ground. Why 15k? Nearby water lightning strikes.

DC presents no shock threat.

Yes and it is a good thing that boats don't have 80+ VDC which could be a threat.

Good info on this post for sure.
Jim...

PS: I checked my Stainless Steel Rudder post with my Ag/AgCl reference probe (-0.01 mV) so it is either totally isolated or passive SS. No zinc needed.

 

[fredanderson2000]

Everybody with the ground plate connected to keel bolts on the bilge floor be careful. Yes, thee will be current flowing through the wires to the keel, and yes it is because of vampire currents. The problem that this causes is when boats get to be a certain age, the stainless plates, bolts and nuts start to corrode, especially when they are on the floor of the bilge. This corrosion will cause some arcing that will rot the bolt holding the plate. I wrote about my experience on a 1992 Legend 33.5 on the Hunter Owners site a few years back (http://hunter.sailboatowners.com/mods.php?task=model&mid=29&mn=33.5). After repairing the bolt, I relocated the plate above the floor of the bilge so it would stay dry. My current boat, MH 40, will have a similar problem. Part 2 of the solution is to run an auxiliary cable (larger means lower resistance and is better) to host a secondary zinc plate to expose more square inches to be sacrificed to the electrolysis gods (or your neighbors mis-wired boat). My plate is a 6" x 6" and cost around $5. A stainless bolt on the transom is connected to my sail-drive with AWG10 wire. The run is about 12 foot. The zinc cable attaches to the bolt with a wing nut when in port. It is removed and stowed when underway.

 

[Charles Erwin]

If you connect (bond) your saildrive or engine to any other underwater metal you need to read and completely understand the attached notice.

FWIW the Volvo version is different but overall saildrive type units (that includes any outdrive propulsion) need to be carefully monitored - and particularly so in a marina.

Charles

 

[fredanderson2000]

Good point Charles, if there is enough resistance difference between the 2 anodes, it is possible to have the 2 zincs feed from each other. I believe that it is more prudent for me to bolt the zinc cable to the engine that is bolted to the sail drive. This will remove some of the burden from the sail drive zinc. It is important that this be the same material. I do agree with the article, and have the proper isolators on board. In addition, the boat is kept at a private pier (only boat) and only plugged in on weekends. My closet neighbor is 100 yards away. I do worry about the galvanic issue and know it becomes worse with the sail drive.
I currently have the sail-drive painted with the Interlux system (epoxy/primer/trilux33). I have the original 3 blade aluminum propeller as well with the same treatment (it does pretty good). After speaking with the Interlux folks, they say they have an improved formula for their trilux (compared to the formula I used last spring).