Thanks for all the comments.

Ideally I'd indeed like to have an isolated engine which would make my
dc system completely separated from the hull. It might be easy to do
if you have the money to buy a new starter motor, alternator and
senders, but I'm currently not in that position.

I'm now thinking of the second best option. Obviously I'll track down
the ground leak and correct it first. But then, what to do with the
engine? Put a ground wire to the hull or not?

Currently there is no ground wire. That means that any ground leak
takes current through the seawater to my prop/shaft or engine
internals (via cooling water) and via the engine negative wire back to
the battery. It eats away my expensive parts and paint.

If I would ground the engine to the hull, any ground leak would follow
the steel of the hull to that extra ground wire and via the engine
negative back to the battery. Hereby I assume that the path via the
steel is more attractive than "outside" via the sea water. I'd say
this is a better situation than the current because no electrolysis
takes place.

I'll post my problem to rec.boats.cruising too, see what they think.

Joost

On Tue, 5 May 2009 02:19:09 -0700 (PDT), joost
wrote:

Thanks for all the comments.

Ideally I'd indeed like to have an isolated engine which would make my
dc system completely separated from the hull. It might be easy to do
if you have the money to buy a new starter motor, alternator and
senders, but I'm currently not in that position.

Well, I have a conventional starter and alternator and my engine is
isolated from the hull and propeller shaft.

The flexible engine mounts and a plastic flex plate between the engine
and shaft engine mount insolate the engine from the hull...

I'm now thinking of the second best option. Obviously I'll track down
the ground leak and correct it first. But then, what to do with the
engine? Put a ground wire to the hull or not?

You should do that.

As far as bonding goes, how is the engine coupled to the negative
terminal on the battery? In most cases there will be a "battery cable"
connection between the engine and battery. If so then this is
sufficient. Assuming the engine - battery connection what do you
expect a second wire connecting the engine to the hull will
accomplish?

Currently there is no ground wire. That means that any ground leak
takes current through the seawater to my prop/shaft or engine
internals (via cooling water) and via the engine negative wire back to
the battery. It eats away my expensive parts and paint.


If I would ground the engine to the hull, any ground leak would follow
the steel of the hull to that extra ground wire and via the engine
negative back to the battery. Hereby I assume that the path via the
steel is more attractive than "outside" via the sea water. I'd say
this is a better situation than the current because no electrolysis
takes place.

What ground leak? You should not have any utilities like lights,
radios, etc., that are electrically connected to the hull.


I'll post my problem to rec.boats.cruising too, see what they think.

Joost

Cheers,

Bruce in Bangkok
(bruceinbangkokatgmaildotcom)

Joost,
There have been many really good replies from the other responders, so I
won't repeat the good advice of others, but here is a tip. Connect an LED
from DC ships voltage to the hull in an obvious location. If the LED is on,
you have a ground fault, fix it. Secondly, make the engine common to the
hull and not common to DC return, it's less expensive than isolating the
engine and the result is the same. Thirdly, your problem might not be on
your boat, but on the dock. When connecting shore power to your boat, never
connect the safety ground at the outlet on the dock to your hull and always
connect your AC ships ground to the hull. However, to meet code the Dock
ground needs to be connected to the isolated frame of the isolation
transformer. If you don't have a transformer, you won't comply to code, but
the solution still works and is safe, because the sea is still common to the
reference at the distribution transformer.The problem is that other boats
electrical leaks can cause electrolytic corrosion to your hull because their
DC system is connected to their ships ground and it is common to their power
outlet on their dock. It is paramount that you isolate yourself from the
electrical problems of your neighbor(s). Lastly, if you have a paint scheme
fault, you must sandblast to bare metal and redo the entire bottom
correctly. Do not do the latter until you complete the former.
Steve

"joost" wrote in message
...
Hi,

Last year when I hauled out my steel boat I found many paint blisters
on the bottom. When I opened them, clear grey steel came out
underneath. I then suspected a ground leak causing electrolysis to be
the problem. There was indeed a leak on the RF ground of the shortwave
radio, which I fixed by adding capacitors in the ground path.
According to my measurements then, no more ground leaks existed. I
scraped off all the blisters and repainted.

Today I was overwhelmed by a feeling of sadness when I discovered that
there is a whole bunch of new blisters at and below the waterline. The
question that I would like to ask is:

Are there other causes for this type of blistering than electrolysis?
The size of the blisters is about 5-25 mm.

Thanks,
Joost.

"joost" wrote:

Ideally I'd indeed like to have an isolated engine which would make
my
dc system completely separated from the hull. It might be easy to do
if you have the money to buy a new starter motor, alternator and
senders, but I'm currently not in that position.

You basically have a "pay me now or pay me later" situation.

Either way you pay.

One way you get an isolated engine, the other you don't.

Lew