Your measurements will tell the story, Larry.

We tend to believe that salt water is a great conductor. Compared to
fresh water, it is some orders of magnitude better. Compared to metal
conductors, salt water is many orders of magnitude worse. Dirt and sand
are even worse conductors than salt water.

Here's an even simpler experiment. Take a couple of one foot lengths of
copper pipe attach a 20 foot wire to each and connect the wires to an AC
voltmeter. Drop the pipes into the water with say 20 to 40 feet of
separation. If your boat is in a marina, there is a chance you'll detect
an electric field in the water with this setup. If you find one around
your boat, switch the meter to AC current and see if any current flows.
Because the "probes" are not dissimilar metals, any current you detect
will not be due to a galvanic couple. Now connect one of the "probes" to
the AC grounding conductor while leaving it in the water. Remeasure the
voltage and current. Does it drop to zero?

In the other experiment, you'll be creating an electric field.

Next step is to consider that happens to conductors in electric fields.

But if you've got a copy of either of Beyn's books handy (The 12 Volt
Doctor's Practical Handbook, or The 12 Volt Doctor's Practical Handbook
for the boat's electric system) you can read up on these fields.

Chuck

Larry wrote:
chuck wrote in news:wV3Sf.4616$sL2.2779
@newsread2.news.atl.earthlink.net:


We can just multiply by ten to get the 120
VAC current.


I don't think it's linear, actually. The curve would be more log-like.
The transformer would show it, though.


Turns out that the lethal situation for swimmers in the presence of
these strong fields is far worse in fresh water than in sal****er,
contrary to one's initial expectation. In sal****er, the current is so
overwhelmed with little high-conductivity paths around the swimmer that
virtually no current passes thru the swimmer.



This is why I don't think I'm in any danger ungrounded like that. The
same principle of the swimmer being a greater resistance is true of our
underwater prop. The path DOWN under the offending boat in your scenario
is much easier than trying to get the current to go from his little prop
to our little prop sideways away from the giant ground 15' under the
keel. The current distribution is going to be massive down but very
little sideways. Unless I'm DIRECTLY connected between the underwater
metal and AC ground or neutral, I'm completely insulated from any path,
whatsoever! Even if his boat is turning the water blue with current, If
I just touch the engine block, I'm totally isolated. If I'm touching an
insulated appliance, I'm totally isolated. The scenario becomes very
absurd, very fast, not a normal condition that might happen. The one
engine-to-AC line possibility might be if I touch the engine and the
water heater's grounded case simultaneously. There might also be a
current path through the fresh-water-cooling loop the water heater
connects to the engine with. If this loop is conductive, the heater is
already semi-grounding the engine block to the AC line, but I've never
seen any evidence it makes a difference. We moved the water heater out
of the engine room into the portside deep locker to get the heater out of
the way of engine belt and impeller maintenance on the front of the
Perkins. I never thought of this current path through the hot water
heating hoses before this morning. Interesting. Being fresh water
contaminated with antifreeze I'm not sure what its resistance would be.

There's no galvanic current to the dock through that hose I can
measure....