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The following is an article
written by Vern Linkhorn, electrolysis authority.
Is my vessel safe from Stray
Current in the Marina?
This question is being asked more
frequently these days and basically the answer in most of New Zealand is
YES. All marina complexes must have their shore power supply equipment
conform to Electrical Power Supply Authority Regulations. This means
that the power supply to any vessel must be through an isolation
transformer or earth leakage detection outlets. As you go around
marinas, this equipment is quite obvious at intervals down most marina
berth fingers. In earlier type installations it was usually done with
isolation transformers which proved to be expensive to operate and
maintain for marina groups, but kept the vessel's hull and cathodic
protection system isolated from the dock. As the earth leakage detection
systems became more popular and less expensive a lot of the original
equipment was replaced.
This is now where most of the recent
problems have appeared for boat owners, especially those who leave their
vessels permanently connected to shore power for running equipment such
as battery chargers, hot water cylinders and refrigeration units. But it
would be very unusual for this to cause actual stray current corrosion
to vessels in the vicinity. The corrosion that is actually still
occurring in these vessels is the same old Galvanic Corrosion. This type
of common corrosion attack occurs on any vessel whether it is connected
to shore power or not. In fact it happens to many vessels not
necessarily in marina environment.
How then does shore power make any vessel
more susceptible to this type of corrosion attack you may ask.
If your vessel's AC-system is wired as
per current electrical regulations, as it should be, the earth wire will
be connected to the DC ground or negative and in turn to the bonding of
the boat's corrosion protection system. When the AC shore power lead is
then connected to the vessel, EVEN WHEN NOT SWITCHED ON, you in fact
connect to every other boat in the marina that is also on shore power,
via the earth leakage detection system. You are also connected to the
marina structure and your cathodic protection system is protecting it
from attack. This will cause your zinc anodes to deplete at a much
faster rate and they will not last for a period of time that they
usually do. Because of variations in different boat's requirements for
levels of cathodic protection, by all being connected together via the
AC power, some vessels will be either under or over protected with the
subsequent detrimental effects.
Random, checks have been carried out on
several vessels connected to shore power in the marina complex with
mixed results, but on average, most were in some way affected. So how
can the boat be isolated from problems while on shore power.
Firstly, the facts:
- The corrosion attack occurring on
vessels in the marina complex is usually traced to natural Galvanic
type problems.
- As all boats are generally isolated
electrically from each other by mooring lines, the only time another
neighboring vessel can affect your boat is by the common connection to
shore AC power.
- There is a requirement to protect all
vessels and their occupants from the chance of electric shock by way
of either earth leakage detection devices or isolation transformers.
- Any stray current problems that do
occur with the AC or DC electrical systems in a boat will usually only
affect the vessel that has problem. This is true electrolysis.
Secondly, the immediate answers:
- Shore power leads to the vessel should
be of heavy duty quality to preclude the possibility of stray current
corrosion damage to a boat due to voltage drop problems going back to
the marina structure.
- The vessel should be checked to ensure
that it's AC electrical system is safe and conforms to local
regulatory requirements.
- The AC system on the vessel should be
fitted with an isolation transformer or galvanic isolator to again
isolate it from other boats and the marina structure.
- Have your boat checked for any
corrosion problems that could be occurring, whether it is galvanic or
stray current before accusing other vessels in your vicinity.
This is normally carried out while the vessel is still in the water.
- Corrosion problems can be prevented or
at least controlled so as to allow you safe and happy boating.
If you would like to discuss your own
situation, please contact direct:
Vern Linkhorn
Phone: 09 520 0520
Mobile: 0274 792276
Email:
marinecorrosion@clear.net.nz
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