earth in a steel yacht

[Ike]

Comparing a boat sitting in water, especially saltwater that is very conductive, to an auto chassis is an invalid comparison. The hull is never used as a conductor in boats, This is common in automobiles, but in a boat results in serious problems, stray current corrosion (not electrolysis, they are two different chemical reactions), and stray currents that can be deadly to life.

[Frosty]

Not only the above but when you hit the starter all that power 300 amps or so will try to get back to the batt. If there is no cable at least the size of the starter feed cable the power will go down anything it can such as welding your control cables solid.

[MikeJohns]

Originally Posted by Fanie

Perhaps a simple way to explain why you don't use the body (or hull) to conduct current through. If you push the + and - leads of a battery in the sea water it begins to boil the water.

This is due to the salt water being conductive. If you pass current through the hull then the same effect may take place - even a very small voltage drop over two point will cause conduction. ...................


If you generate AC then both L and N should be insulated from earth. To prevent static buildup for whatever reason a 10K 5W resistor is usually connected between one AC wire (Neutral) and ground.

But the reality is that there is a conductor say 1m2 in cross section aluminium for a small ship hull, it's insulated from the seawater ( epoxy paint coating ) has the connections introducing the leakage current above the waterline ( inside the hull ) and has a bare anode in contact with the seawater close to each end of it's immersion.

What possible sensible mechanism could be suggested for this to cause corrosion of the conductor ?
Lets say we put a fault leakage current from a damp connection of 300mA returning through the hull: You won't get any effective current flowing in the sea water, because there will be no effected voltage across the conductor.

In Australia aboard ship the Neutral must be directly tied to the earth, the ships hull is also earthed. That doesn't cause any problems at sea whatsoever and is considered the safest setup.

[michael pierzga]

The problems I see caused by stray electricity are not on the hull...they are in the yachts systems. Many wet disimilar metals.

[MikeJohns]

Originally Posted by michael pierzga

The problems I see caused by stray electricity are not on the hull...they are in the yachts systems. Many wet disimilar metals.

There shouldn't be any exposed wet electrical connections ever !
Nothing would last , even tinned copper wire corrodes rapidly when exposed to salt water.

[michael pierzga]

Its plumping, pumps, oil coolers, rudder beaings, keel bolts...the list is long

[MikeJohns]

Yes on a wood or GRP boat but not on a steel hull which is what we are talking about.

[michael pierzga]

Im talking about Metal boats. I have very little experience with system intensive wooden boats, only 30 years with steel and Alloy yachts