I wish I had gone with a degree in engineering instead of finance. Because when I read about how to test for this and that it hurts my head.

So with that said here are my concerns: It's a 75 model. I had slight pitting near the stern. I pulled it, sanded it to bare aluminum, then etched it out with acid, then applied some goop stuff to seal it off. (This stuff was recomended by a couple local marinette mechanics)

#2- During the summer when I'm all hot and sweaty and down in the motor room. When I slightly rub against my 3208 it feels, very slightly, like an electrical current exists.

I know the boat has a huge galvonic isolator installed. And there are no steel hulled boats within 100 feet.

So what do I check? And how?

How can I check if the docks are grounded correctly? How about the motors?

Can someone dumb this down to a bankers level.

I can think of at least 700,000,000,000 reasons why you were smart to choose banking rather than engineering for a career.

But, back to boats. Your engine should be connected to the hull via the battery ground lead. Use a multimeter to check for both AC and DC voltage between your engine block and your hull.

Unplug your shore power from the boat, and measure the dc and ac voltage between the ground slot (the one with the "hook" in it) and your boat's hull. You should see no dc and no more than a few volts of ac, perhaps 5 or six. If this fails, then your marina wiring has a problem. The marina ac is grounded (to the actual ground) at the transformer (usually on a pole) and if the dock wiring has problems you will see voltage between the water at your boat (measured at the hull) and the ground that the marina gives you.

The isolator is supposed to block current flowing from the marina ground into/outof your hull, while at the same time providing safety if a hot ac lead shorts to your hull. It should show very high resistance when measured with a multimeter, but that isn't enough to prove that it works. A good tech can determine what its "threshold voltage" is.

I don't trust galvanic isolators. I would get an isolation transformer.

With the boat unplugged from the dock, measure the resistance from all three leads to your hull. If there is any connection (low resistance) then try to find and fix it. You can do this by disconnecting one thing at a time until the short goes away. First, of course, everything that is plugged in. Then disconnect circuits behind the power panel until you find the baddie. I had a nasty short in a 12V/120V blender in the galley, easy to find since it was plugged into an outlet. I threw it in the dumpster and then covered it with other trash to keep some soul from salvaging it and maybe screwing up their boat.

As for that other thing, Jeff, it's where you give all of your money to somebody, and they give you some of it back....

Dang it, you guys. Now I'll never understand what an annuity is!

Jeff

I signed on today to ask if anyone has opinions on this latest gizmo from Marinco, it's advertised in the current (no pun intended!) West Marine ad. Is it something that can help us maintain our vigilance or is it only for the things that should be obvious anyway, such as reverse polarity at the dock?

http://www.marinco.com/product/galvanalert-shore-power-corrosion-detector

Since it seems to fit with this topic, I thought I'd add it into this chain.

I always appreciate the knowledgeable answers from Jeff and Doug regarding all of the unending questions the rest of us have on this issue. I wish I had studied EITHER investing or electrical engineering, but since I didn't, I'll just keep on reading the Forum.

JIM

This thing seems to have two functions: it detects reversed power and return (black and white) and detects direct current in the ground (green) wire. It looks very easy to use, just put it in line with the shore power cable.

Reversed power and return is a BIG safety concern, since all the gadgets on the boat are designed to keep you away from the hot (black) and aren't so concerned about the return (white) because white is at the same potential as the green, and the boat, approximately.

You can get a tester for a few bux at Home Depot or the like that plugs into a socket and shows various faults with little lights. This will test for reversed power, among other things. I leave one plugged in where I can see it. It has the advantage that it can be moved to check all the sockets, although you will see reversed power in ANY socket. When my marina was rewired, power was reversed on one of the docks, so don't trust even professional wire guys.

The electrolysis meter measures the voltage between the water and the boat hull, so if the reading is within spec (0.9 to 1.2) then the hull should be fine. If the reading is not within spec, then one of the causes could be direct current flowing in the ground (green) wire from the dock. This is tough to measure with a meter unless you have some provision for breaking the ground (green) wire while keeping the other two wires (black and white) connected. The gizmo does this very neatly. If there is direct current flowing, then the galvanic isolator in the green wire is defective.

I am not sure about $150. You can buy a nice multimeter for that. Not to mention the beer.



As far as I know, it is not. You should have a heavy wire running from the block (at the starter preferably) to the battery negative terminal, and another smaller wire running from the block to the hull. The factory provided a stud between and forward of the engines on my boat. You could also have a heavy wire running to the stud on the hull, and another heavy wire running to the battery negative terminal. This is electrically the same, and is convenient but adds another connection for the starting current to go through. Either way, you should have no resistance between engine block and hull. This differs from a gas engine only in the fact that you have a starting circuit but no ignition circuit.



Use a multimeter and measure between a clean spot on the engine block and a clean spot on the hull. Verify the lead resistance by measuring with the two leads together. Subtract this lead resistance. You should be well under an ohm, my Perkins show no resistance at all on my cheap meter.



If your block is not connected to your battery negative terminal, you would have noticed by now. It is possible that both block and battery are not connected to the hull. If so, I would recommend a yellow wire, of at least the same size as the alternator output (red) wire, from a starter mounting stud to the ground stud on the hull. This should be the ONLY connection to the hull for all the motor circuits.



Plug the boat in to dock power, and turn it on. Put your multimeter on ac. Find the shore side of the galvanic isolator and put the probe on the terminal. touch the other probe to a clean spot on the hull, anywhere will do. Some voltage is normal, but more than 10 volts ac is a concern. Make the same measurement with the multimeter on dc. DC voltage will be slight, if any. More than a few volts is a concern.

Move to the boat side of the galvanic isolator and remeasure ac and dc voltage. The voltages should be gone. If they are the same as before, then the isolator is toast, and it is not grounded to the hull. Lift the ground to the hull and measure again. Voltages should still be gone, although some electronic meters are so sensitive that they will register (I prefer needle meters for this reason). If it looks fishy, take out the galvanic isolator and take it to a tech for testing.



Turn off all your ac breakers except for the main breaker.

Disconnect the shore power cable from your power inlet. Conveniently, all three wires are there, on prongs. The prong with the bent edge is ground ( green), the middle-sized one is neutral or return (white) and the small one is hot (black).

Find a bare spot or screw for the hull connection. Put the other lead on another screw, and measure resistance. No resistance means you have a good hull connection. Move the other lead to the bent-edge prong. You should see a high resistance, because the galvanic isolator is between green and the hull and it is not supposed to pass dc. Check the neutral lead. It should show very high resistance because it doesn't connect to the hull anywhere. Check the hot lead. It should show very high resistance also.

Turn on all your ac breakers. This connects the hot to all of your loads. Note that the neutral is not switched: all neutral is connected together.

Recheck the isolation of all three prongs. They should still all be high. If they are not, then you have a short inside some ac appliance, and you can find the offender by disconnecting things one at a time.

Remember: The green wire, once it is past the isolator, is hull. The best way to mount ac appliances is to isolate them from the hull, attach the green wire to the frame of the appliance, and then hook up the hot and neutral. Neutral is at the same potential as the green, but must absolutely not be connected to green. If it is, then you have neutral all the way from the dock to your hull, unprotected by an isolator. When your appliance is isolated from hull and grounded with green, then any leakage from the hot lead goes directly back to the dock through the ground wiring and the isolator -- there is no current through the hull itself. Of course, if the leakage becomes a short, then a breaker opens.

I have a diagram of what your ac circuit might look like at http://www.geocities.com...ette_Wiring_Generic.pdf

Matt:
Sorry for the confusion. Both diesel and gas engines are typically grounded to the hull in Marinettes.
Sometimes, an additional negative cable is also run from the negative battery terminal to the starter or to the block of a diesel engine because of the higher current needed to start a high compression diesel.
The only reason I mentioned it was because you touched the engine and felt some electricity. If you had gas engines which use a coil to boost voltage from 12 volts to 8,000 to 40,000 volts for the spark that ignites the fuel, I might suspect you touched the plug wires or distributor cap.
But diesels don't use electricity to ignite the fuel. They use compression. So we can eliminate any 12 volt DC source and look for a 120 volt AC source as Doug suggests.

as long as products have been mentioned, how about the Corrosion Reference Electrode at boatzincs.com?
sittin duck