Somebody wrote:
................................................. .......................
Unfortunately, giving the starter and alternator a separate ground
connection is not an easy thing to do reliably.
................................................. .....................

================================
It's very easy to do.

You need a cranking motor (starter) with an isolated ground which is
standard construction, if you specify it, and an alternator with
isolated field terminals as well as isolated DC output terminals.

Again, standard hardware, if specified.

All senders (oil pressure, water temperature, etc) must be 2 pole
units with insulated ground terminal.

The above give you an electrically insulated engine.

SFWIW, the above equipment is needed in the world markets since some
parts of the world use positive rather than negative ground.
====================================

"Bruce in Bangkok" wrote:

O.K. here we go.

First of all the DC electrical system should be insulated from the
boat. No grounding, no nothing! The reason is that there is no
requirement that the DC system be connected to the boat and if it is
it can cause problems.

Agreed. It is an absolute MUST on a metal boat..


Usually the engine mounts insulate the engine from the beams on
which
it is mounted and a plastic "flex plate" can be used to insolate the
propeller shaft from the engine.

Doesn't buy you much since sea water cooling will be involved.


Radios usually need a "ground plane" that is essentially the
"ground"
side of the antenna circuit. This can be isolated from the hull by
the
using capacitors.

Yep.

See recent post on rec.boats.cruising by Larry, et
al.

Assuming that you have a steel boat that is built properly the only
dis-similar metals you have in contact with sea water is the
propeller
so with a completely isolated electrical system galvanic activity is
kept to the minimum.

True.

You do still need zincs but the need is less.

True.


Bonding - as there is no dis-similar metals then you do not need
bonding.

Agreed.

Lightning protection - as the entire hull is in contact with the
water
and the mast and stays are not insulated from the hull the boat is
effectively grounded for lightening strikes.

No comment.

Radios - Most radios use a "single sided antenna circuit" in other
words a wire leads from the antenna terminal on the radio case to an
antenna. the other side of the circuit is provided by a "ground
wire"
to some sort of ground.

The ground side of the antenna circuit can be isolated from DC
ground
by connecting it through a capacitor to the hull. See above.

Note: that some radio antennas are "two sided" and both the ground
and
"hot" connections are made to the antenna. A "case ground" does no
harm in this case.

A.C. Power - AC power is more complicated and I won't go into it in
detail, but basically you can totally isolate an on board AC system
and treat it similar to the DC system but if you use "shore power"
you
have different circumstances.

Isolation transformers are an absolute necessity on a metal boat.

A transfer switch is required if an eng-gen is on board.
===============================
AC distribution on a boat, especially if an eng-gen is in service, is
a totally separate subject.
===============================

Commercial A.C. electrical power has connections to the physical
ground (the planet/ground/earth/dirt) and thus to a boat, through
the
sea water. Because of this connection using commercial power (shore
power) without a ground circuit is extremely dangerous as standing
on
a steel deck with bare feet and touching a live AC wire could very
well result in death.

No comment at this time.


Resolving this situation is fairly straight forward but in the
interests of brevity I'll not cover it here as it gets a little
complex - Isolation transformers 'n all that...

For good electrical/electronic information you can ping Larry over
in
rec.boats.cruising as he is really knowledgeable (albeit outspoken).
There is another guy over there and I am embarrassed to say I don't
have his name (sorry mate) so you can get good information there.

Hope this helps.

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

Lew