Hamilton Jet HJ241, Manual

Page: 57 / 202

4.3
4 PRECAUTIONS AGAINST CORROSION
4.1 G
ENERAL
HJ-241 / HSRX
have a direct path back to the battery negative or the
AC source.
Alternatively, this connection to the battery
negative can be deleted Provided that the
following are carried out:
1. There is a two wire normally current conducting
electrical system which is isolated from the Hull,
Jet Unit and Engine,
2. There is an effective leakage monitoring system,
such as the "Test Light" system, which is used
regularly and the results are recorded.
Without the bonding system to battery negative
connection, stray current corrosion is possible and
it is important to check for leakage:-
a) For every item of electrical equipment in
operation.
b) When there is any alteration to the electrical
system of the boat.
c) When any electrical connection is made to
shore.
4.1.3 Corrosion Monitor
It is recommended that a corrosion monitor be
fitted.
The corrosion monitor should be a high impedance
device. There must be no possibility of an electrical
connection between the Jet Units and the ships
batteries.
If the Jet Units are isolated from the hull, corrosion
monitoring of each Jet Unit external wetted surface
and internal Intake Duct should be carried out.
If the Jet Units are electrically connected to the hull,
corrosion monitoring of the hull only and each Jet
Unit internal Intake Duct should be carried out.
4.1.4 Trim Tabs and Other
Submerged Fittings
When 2 dissimilar metals are electrically connected
and submerged in a seawater, then galvanic corro-
sion can occur.
If a large stainless steel fitting (such as a trim tab) is
electrically connected to the jet, then the corrosion
protection of the jet unit will be compromised. In or-
der to ensure adequate corrosion protection for the
jet, stainless steel trim tabs should be fully painted
or electrically isolated from the jet unit, or prefera-
bly both. Normally an anode would be fitted to the
trim tab to provide corrosion protection to the tab.
Trim tabs made of aluminium will not affect the jet
corrosion protection.
4.1.5 Earth Plate Connections for
Electronic Transmitting
Equipment
Radios, radar and other transmitting equipment
should Not use the Jet Unit for an earth plate but
must have a separate earth plate.
Be guided by the installation instructions for the
radio; radar equipment etc, but in general these
systems should be electrically insulated from the Jet
Unit
except that both the earth plate and the metal
casings of the electrical transmitting equipment
should be connected to the earth bonding system.
1. An area of metal plate is required which is not
painted and always immersed, even when at
planing speeds. It is always in electrical contact
with the sea water.
2. The area of metal plate is typically
approximately 400 x 400 mm and should be
located close to the equipment radiating
electrical waves but well forward of the Jet Units.
3. For a metallic hull, the earth plate can be a
thickened area of the hull, formed by welding
additional plate inside the hull skin, up to 25 mm
thick.
4. For a non metallic hull a separate metal earth
plate must be fixed externally to the hull. It
should be of material compatible with both the
"bonding strip" and hull (stainless steel is likely
to be the best option. It is not advisable to use
copper as it can cause corrosion problems for
other metals).
5. The "plate" should have a large stud welded to its
centre and protruding inboard to which all the
zero voltage wires from equipment can be
connected to.
6. The earth plate should be connected by an
insulated wire to the vessels "Earth Bonding
System".