How Important is this Ground Thingy ?

[dandrews]

+1

This is completely in line with how I read Wing & Calder and their take on ABYC standards.

Don

[senormechanico]

Originally Posted by osirissail

Please explain that better. If the transmission is raw water cooled, then the transmission is "grounded" to the sea water - or at least to its heat exchanger.

For a transmission to be "electrically isolated" from the engine, the spline shaft from the transmission has to be received by something non-metallic that is attached to the engine flywheel assembly. And the bolts between the transmission and the engine have to be isolated by something that does not conduct electricity.

There should be something in the Volvo engine manual that describes what, how and why they did that. It seems like an awful lot of additional expense in "isolating" parts over just bolting the whole thing together like most all other marine engines. Easy way to find out, is to use a VOM meter and put one probe on the engine and the other probe on the prop shaft/lower unit and see if there is an electrical continuity.

Believe me, I've read the manual over and over. There is no explanation of why they did it.

There is a decal on the transmission with an earth ground icon with a circle and slash through it.

I'd go out with my multimeter to measure it right now as well as take a pic of the warning decal, but it's dark, raining and close to snowing.

The cooling water goes into the transmission case (which I think is aluminum), then out to the engine's raw water cooling pump via a rubber hose.

While I have a shaft drive with a folding prop, the manual specifies BOTH the reverse drive and S drive having the insulator between the trans and engine block.

[four winds]

Seems to me there would have to still be continuity to the prop.

Assuming the output shaft of the engine and transmission gears are metal the prop would be electrically connected to the engine's crankshaft.

Could be an attempt to protect the in-water housing of the drive unit by providing a better ground internally.

[four winds]

I'm cleaning up the wiring on my 78 model US made boat. Removed a wheel barrow full of old no longer used wiring and drawing a wiring diagram.

From the factory the DC ground bus, bonding bus, and AC green safety ground are all connected together via jumpers. And connected to the engine block.

Also a large ground from the mast base comes back to the block. I took a loop out of it today. It wasn't original to the boat and was too long so the OP just looped it. Same with the bilge pump wires. They were about five feet to long a just coiled up in the bilge.

This thread is interesting to me and I am considering what, if any, changes I would make.

[osirissail]

Originally Posted by senormechanico

Believe me, I've read the manual over and over. There is no explanation of why they did it. . . .

The cooling water goes into the transmission case (which I think is aluminum), then out to the engine's raw water cooling pump via a rubber hose. . .

I think that is your answer. There is a long history of outdrives and saildrives getting "eaten" by electrolysis in their early days. The non-steel(iron) alloy used to make the saildrive if electrically connected to the engine appears to be highly susceptible to dissolving. They even use aluminum anodes rather than zinc. See SA post #
6

Classical iron/steel engines and transmissions and propeller shafts don't have this drastic a problem with electrolysis.

[Ex-Calif]

Originally Posted by four winds

Seems to me there would have to still be continuity to the prop.

Assuming the output shaft of the engine and transmission gears are metal the prop would be electrically connected to the engine's crankshaft.

Could be an attempt to protect the in-water housing of the drive unit by providing a better ground internally.

If the engine spline goes into a clutch pad and the clutch pad is non-conductive (i.e. a pressure plate set up) then there could be no metal to metal contact between engine output spline and transmission input spline.

[four winds]

Didn't consider that, mines all metal with a cone clutch setup.

However, I'm familiar with pressure plate/clutch setup from working on cars which are usually equipped with a pilot bushing (usually bronze) or bearing that connect the transmission input shaft front tip end with the back of the crankshaft for stability and alignment.

Without this when the clutch is disengaged the shaft and disc would be free to move laterally via balance and clearance in the input bearing to the transmission.

Not saying the OPs setup is fitted this way, but I'm betting it is.

[bartonman]

If you can afford it, installing an Isolation Transformer will keep the stray electrical current from causing the severe galvanic corrosion.

[Ex-Calif]

Originally Posted by four winds

Didn't consider that, mines all metal with a cone clutch setup.

However, I'm familiar with pressure plate/clutch setup from working on cars which are usually equipped with a pilot bushing (usually bronze) or bearing that connect the transmission input shaft front tip end with the back of the crankshaft for stability and alignment.

Without this when the clutch is disengaged the shaft and disc would be free to move laterally via balance and clearance in the input bearing to the transmission.

Not saying the OPs setup is fitted this way, but I'm betting it is.

Yeah, pilot bearing will do it.

Seniormechanicos diagram is pretty clear in that case. The sd is isolated and that should be a good thing. It may not be at the engine interface as depicted but some other way in the leg or something. The picture could just be for clarity. Ohming it out would clear things up pretty quick.

[capn_billl]

The transmission may have an asbestos friction plate. If it is aluminum, they probably have it that way for a reason. Back to problem. Start at battery, go through all wires, check for any cracked insulation, corrosion on a positive wire, then check all grounds to engine/grounding plate. Chances are this will find your problem.

[Jetexas]

Thanks to some major help from Seamonkey who volunteered to go through all my wiring with me, two hours with a multimeter revealed that my DC system was clean and wired correctly, but that I was getting charge on my AC ground. After mentioning this to a neighbor a couple boats down the dock, they said that their shore power had shorted out caught fire just a couple weeks ago. We have several rather derelict boats on our dock, and one in particular has sunk twice in January. It's now sitting with an oil boom around it. I'm guessing it's the culprit that is causing the misery for the rest of us.

The fuel gauge issue turned out to be totally unrelated. The new float I'd put in the tank back in November had been bad straight out of the box. I bought another one and voila. Miraculously West Marine still accepted a return on the non-functional one despite the fact that it had already been cut to size and soaked in diesel.

[Sailmonkey]

AC ground current was around 70ma from the shore conductor to mass, on a nice day.....who know what will happen when summer arrives and air conditioners are running!!

[kefroeschner]

Originally Posted by goboatingnow

Why in the same of god would you want to connect DC negative to seawater ground. It serves no purpose whatsoever and in fact promotes impressed corrosion. It is never done in European boats. The engine is connected for the reasons you give, but that's it.

Dave

Yes.

As to Ike's statement that 'ground' is at zero voltage potential -- voltage is measured between two points. It is meaningless to say that any point is at 'zero voltage.' (The earth itself is at something like a million volts potential relative to the upper stratosphere -- thus lightning.) And as many keep trying to point out in these threads, trying to establish a boat ground at the same potential as everyone else's is a losing (i.e.corrosive) endeavour. And as I've said before, most US harbors are a big electro-chemistry experiment. Do not participate.

[capn_billl]

Originally Posted by Jetexas

, they said that their shore power had shorted out caught fire just a couple weeks ago. We have several rather derelict boats on our dock, and one in particular has sunk twice in January. It's now sitting with an oil boom around it. I'm guessing it's the culprit that is causing the misery for the rest of us.

Very likely, in fact I would insure to drop power to the sunk boat for everyones safety. Demand the harbormaster verify no AC to the water, or unplug yourself, and move), until they fix it. This is one of the many reasons they discourage swimming in a marina. It can also wreak havok on the other boats electrical systems, as you found out.

[Paul Elliott]

Originally Posted by kefroeschner

It is meaningless to say that any point is at 'zero voltage.'

Except by definition. We can in theory define our local "ground" (whatever that node may be) as the reference for all voltage measurements.

However in practice there is usually a voltage difference between your "ground" and all those other "grounds" out there.