Guru on Marinette electrical grounding?

[martindesign]

As I am working out the bugs on my new problem child I have growing concern of what p.o. has done to this boat. Is there a verdict on whether or not the hull should be grounded to batteries? I didn't think mine was but turns out I was wrong and hull and engines are both grounded to battery ground. My boat does not have a galvanic isolator or a isolation transformer. I am running a aims power 2000w inverter charger. It runs online of shorepower between the boats input plug and the main breaker. The guys at aims said it works (like) an isolation transformer... I have major concerns mostly from the Marinette guys around my dock scarring me with terrible corossion stories. I am pretty sure the marina is partly gulity for this also. I tested with a dvom from my battery ground to the water around the boat and even with all my breakers off and shorepower disconnected (so I know its not my power cause I have no parasidic drains in my boat) I'm reading a voltage potential of almost 2 volts ac and 1 volt dc! Can someone help educate me with what really needs to be done to make this boat same to leave in the water with shorepower on. BTW. P.o. removed the capac. So I have nothing there either. Thanks in advance

[javalin390]

Wow, after reading this, it kinda has me stumped. I have a 1975 37' flybridge, that as far as I can tell, is pretty close to what is was since new. It's had some stuff "modified" and butchered up, but for the most part it's pretty original. I think my engines and batteries ground to the hull, but I'll have to double check. With the recent purchase of my boat, I was blessed with 3 previous owners that kept good records of her, as I have all of the original paperwork, manuals, even the original build contract & sales invoice. It seems to me that one of the books I have tells me that ALL 12 volt accessories are to have their own ground, back to the batteries and the only 12 volt accessory that is allowed to be grounded to the hull is the horn ( due to the fact that it only gets used once in a great while ) I'm not far, my boat is around the corner in Marblehead. I'd like to see how yours is set up.

[martindesign]

Jim, I would like that as well. I can't find any hull grounds other than the horn on mine either. All go to battery also. Do you leave your shorepwoer on all the time? If so do you have any corossion issues? I may just be paranoid because of horror stories but I'd rather not have any surprises. Let me know when you'd like to set something up. Thank you.

[jralbert]

Improper shore power hookups are reportedly more of an electrocution problem (ain't that a cozy thought) than corrosion. DC is the main culprit in that case. In AC, the electrons are constantly reversing direction while with DC they are moving only one way and taking metal from where it's supposed to be to where it isn't. Simplistic but I think you get the drift. I kept shore power up almost all the time (for battery charger and fridge) for years with no corrosion problems. The boat was properly "zinced", engine isolated, and thankfully no exposed DC wires. For the AC side, it had a Quicksilver isolator to reduce stray AC bogies. I could never figure out why but some people cut off their AC ground wire. Hope they raised their insurance at the same time.
There is a way to substitute for the Capac. Jeff Perry (Sir FastJeff) has the device and can explain better its workings. But in summary you dunk a special silver chloride probe into the water. The other lead clips to metal on the hull such as a rail and you can read the results on a meter.
Finally, marinas can be poor stewards of their electrical systems but I am completely clueless on how you ride herd on them (unless a dedicated county or other govt electrical inspector is on the case).

[martindesign]

Joel, is ur hull grounded to battery ground?

[jralbert]

Yes, it was (I no longer own the boat as I note in my signature). Heavy cable connected neg battery posts (both stbd and port battery setups) to an aluminum upright in front of the shelf on which the batteries sit fwd of the engines.

[javalin390]

Also go under the site heading "Electrical & Electronics" where you will find a deeper explanation of the grounds on a Marinette. Some of the guys have a better way of explaining the way AC and DC should be wired.

[barkleydave]

Yes Please check out our other posts. This topic has been covered numerous time.

1. Yes your DC grounds through the hull. On most M's you will see a grounding lug on the forward bulkhead for each engine. From there there is a direct Neg. 12 Batt. connection. It will branch off and a heavy gauge (I forgot how big) will travel up to your helms to a grounding buss bar.

2. Yes your engines are grounded as well. To verify just take a test light from your Pos. batt. terminal and touch the Neg. to the engine block and it WILL LIGHT UP!

3. Our boat fittings ARE NOT BONDED!! This is where a lot of the confusion comes in. On fiberglass boats (especially high quality sailboats) you will find a solid bare copper wire connecting ALL the metal thru hulls, chain plates, etc. This in turn is connected to a Dina Plate which is on the outside of the hull. (a rectangular block of compressed copper beads) This does a couple of things. 1. creates a grounding lightning path, 2. is required to create a ground plane for S.S. radios. (our M's do not normally have SS radios. They are for long range ocean transmissions)

4. Your AC safety ground should go through a Galvanic Isolator or transformer. All this is is a low pass filter (capacitor) which will block stray DC current from flowing from the AC line leaking which can cause corrosion issues.

5. NEVER CUT YOUR GREEN SAFETY WIRE FROM YOUR DOC AC TO YOUR BOAT!

REMEMBER THAT ELECTRICITY IS ALWAYS TRYING TO GET BACK TO COMPLETE A CIRUCIT. (GROUND PATH)

12 volt grounding should be as close to the battery as possible and as clean a path as possible. That is why we run wire directly back to a ground buss which in turn has a clean connection to the battery through the welded grounding lug on the bulkhead.

Poor wet 12 Volt splices in the bilge on bilge pumps etc can cause serious corrosion issues. 12 volt current will flow through the bad splice if in the water and create a low voltage short to ground. Since water is a poor conductor it becomes a very high resistance circuit but that is for another day.

Hope that helps.

safe boating,

dave