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4 PRECAUTIONS AGAINST CORROSION
4.1 G
ENERAL
4.1.6 Anodes
Anodes should not be painted over as they will not
function as intended. If the anodes are being eaten
away they are providing protection. They should be
inspected and replaced when half consumed
because the material that remains will not provide
full protection. It is common for anodes to be
partially covered with a very loose scale. The colour
of the scale depends on local water conditions but
can typically be creamy white, light brown or green.
This scale, providing it is loose (i.e. easily scraped
off with a fingernail), is normal.
If the anodes are not being eaten away, they are
not doing their job and the cause should be
investigated. One reason could be that the anode
does not have good electrical contact between the
component it is protecting and itself. The electrical
resistance should be less than 0.2 ohms.
Poor quality anodes may contain too much iron
impurity. Such anodes tend to form a dense non-
conducting oxide film (usually charcoal grey in
appearance). This condition usually occurs in fresh
water. To confirm this condition, test for continuity
between the anode and the Jet Unit using a
multimeter set to ohms. If the anode has to be
scraped with a knife to get a conductive reading, the
anode is oxidized and must be replaced. Sanding
the anode surface provides a temporary solution,
but it will form the oxide again.
Jet Unit Anodes:—The anodes fitted to the Jet Unit
are made from zinc alloy to US military specification
MIL-A-18001K or aluminium alloy to MIL-A-24779
(SH). These anodes are fitted to the Reverse Duct,
Steering Deflector, Reverse Cylinder and the main
body of the Jet Unit. Anodes are also fitted
internally within the Tailpipe and in most Jet
models, within the Intake.
Hull Anodes:—Further anodes should be fitted on
the Hull, sufficient for Hull protection, as
determined using a portable reference electrode and
digital voltmeter and / or a corrosion monitor.
4.4
The Hull anodes should remain immersed at all
times.
NOTE: Anodes fitted on the Transom of a
planing speed craft will not be immersed
when the craft is at speed and therefore
will not be providing protection.
4.1.7 In Service Checks
In Service, the following three items should be
inspected regularly:
1. The Bonding System: For loose or corroded
connections and test to ensure that electrical
resistance is still low.
2. All Sacrificial Anodes: Replace when half
corroded / eroded.
3. Earth Leakage: There should be no current
leakage from any electrical item to the bonding
system.
4.1.8 Anti Fouling Paint
Anti Fouling Paints
Do not use Copper Oxide based
anti-fouling paints. Do not paint
over the anodes.
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AUTION
4.1.9 Anti Seize Compound
Anti-Seize compounds
Do not use anti-seize compounds
which are based on graphite,
nickel or copper flakes - these will
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AUTION
cause corrosion. Anti-seize
compounds, usually containing
zinc flakes, are available for
aluminium.
4.1.10 Impressed Current Protection
Impressed current protection may be used if
desired. Follow the suppliers instructions.
Impressed current systems should have a "fail safe"
HJ-241 / HSRX
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