App. Note 42 - Marine Electrical & Electronics
Many pieces of marine electrical or electronic equipment function perfectly
when first installed and quite often function perfectly when removed for
Unfortunately, they prove to be erratic in their operation when re-installed
and returned to use in a marine environment.
This type of failure is quite frustrating both to the owner and to the
installer, service technician who has to cope with the type of intermittancies
that cannot often be duplicated on the bench.
What are some of the marine (and other) environmental conditions that cause
Typically, these are those found in coastal or other regions where
a combination salt-spray and/or moisture together with high winds and/or
vibration combine with large temperature variations to produce an environment
which is very hard on electrical connectors.
What are some of the reasons for connector failure under these conditions?
There are two types of failure, either of which can render a piece
of electrical electronic equipment so erratic as to be unserviceable. While
these can generally b classed as either physical or electrical failure
of the connector and although there are some designs in which only one
or the other failures will occur, normally a combination of the two will
The physical failures generally result from the use of connectors which
are n designed for the environmental conditions encountered. Unfortunately,
even with a the thousands of designs on the market today, it is often very
difficult to find connector which will survive some of the more severe
environments. When one is found, the limited market for such a design usually
results in a very high cost. The engineer specifying the connector has
to face the decision of first cost versus replacement/maintenance costs.
It is not unusual for an attractive first cost of the connect coupled with
an apparently low replacement costs to account for the choice of connector.
Often costs due to such items as: unanticipated corrosion due to galvanism
between the connector and the cable, dissimilar metals in a connector an
another part of the equipment housing, as well a5 environmental-effects
due to increasing pollution levels are underestimated. This is similar
to the way in which Ion term maintenance costs due to increased wages are
The most common physical failure results from corrosion eating away
the parts of the connector holding the male and female components together.
The result is that the connector simply disconnects. The cause of the corrosion
is usually a lack of resistance of the connector body material and/or finish
to the combination of salt/water and/or chemicals in the environment; but
the corrosion can be hastened by the use of dissimilar metals. These are
materials which are incomparable galvanically.
Quite frequently encountered is an electrical-based erosion caused
by the use of the connector shell as both a physical coupling and a current
carrying element. This same type of breakdown can occur where a connector
no longer is able to carry its rated current without electrical erosion
taking place. Eventually so much material is lost from the mating contacts
that the actual area of the contact-surface is so reduced that the connector
runs hot, or even gets so hot that it destroys itself.
Assuming that the connector cannot be replaced with a type more suitable
for the climate, and that the connector is still functioning, the usual
solution is to clean all traces of salt/corrosion from the connector and
re-assemble it. The final step may be enclosing it in such a way as to
prevent the entry of the contaminants. This may consist of "buttering"
over the connector body with a high viscosity silicon grease and placing
it in some sort of protective sleeve which will prevent the grease from
being eroded away although because of the potential for silicone-induced
problems the preferable method would be to use a layer of self-fusing tape
followed by layers of vinyl tape and vinyl coating as mentioned later.
In spite of the general use of silicone greases, they themselves can
introduce a form of connector failure, especially when exposed to salt.
Where a silicone is present it can combine with the salt to form a thin,
hard film of sodium silicate that is not only non-conductive, but very
difficult to remove without damaging the connector. Even where silicon-based
water-excluding gaskets are employed in the connector design, migration
of the ethyl and methyl-silane based oils that are often added to the silicone
rubber as softeners can cause problems. These are usually encountered where
a connector is crimped to a cable.
Many physical failures take place because salt water has penetrated
into that part of the connector where the wires are crimped or soldered
onto the pins. Quite apart from the electrical effects of the corrosion
products, these products frequently occupy much more volume than the metal
upon which they feed. Occasionally enough pressure can be generated to
rupture a shell that has already been weakened by corrosion.
Sometimes it is necessary to use a supplementary means of cable/wire
strain relief in order to minimize the effects of wind-induced vibrations
in the cable in causing a "grinding" action between the two halves of the
Another Type of failure:
A third type of failure is the exposure of the connector to unusual
corrosive liquids or gasses not normally encountered in the environment
but which might be generated, from time to time, by other failures in the
operating plant. This can also extend to corrosion-inducing chemicals being
liberated from connector components subject to overheating due to thermal
runaway of contact-wire junctions.
It must also be remembered that there are two elements involved in the
electric failure of a connector: the insulation, and the conductor/contacts/connections;
in other words, the non-conductive parts and the conductive parts.
Dealing for the moment only with the part of the connector that is meant
to disconnect and reconnect (and not with the parts that are attached electrically
or other wise, to the cable) any connector may be broken down into a male-female
or hermaphroditic component which is designed to mate with an equivalent
part, an thereby pass electricity, and the parts needed to hold the former
in alignment. The latter are usually insulators. In many connectors carrying
Radio Frequency signals it is necessary to have the latter parts dimensioned
so that the electrical impedance the connector is the same as that
of the wire. Otherwise there will be a discontinue and a reflection will
occur in the transmission system. This can reduce the effective radiating
power of a transmitter, or cut the signal-strength of a received signal.
Insulation leakage can cause loss of signal strength and/or unacceptable
modification of the signal caused by line reflections. A good example of
the latter is ghosts detail blurring in cable TV.
The result can be a radio, communication system, a GPS or Loran, or
even a radio system that is unserviceable!
Where the RF impedance is not a consideration we still have to deal
with losses in on the electrical insulation. Excessive leakage across the
insulation will result in heating in high-power applications, insulation
breakdown in high-voltage applications, signal leakage in multiple-pin
control circuits. None of these are acceptable, and the consequences could
be destruction of the connector and a fire hazard to consequential damages
due to failure of a process-control, alarm, or communications system.
The introduction of corrosion products into the gap between the connecting
pair connecting means can also result in problems ranging from rectification
effects (most corrosion products can act like crude semiconductors) which
can produce strange modulation distortion of the signals or even introduce
spurious signals derived from the rectification of whatever RF (conventional
RF of even fast rise time) signals ma be present in the environment. Generally
this is characterized as excessive sensitive to "electronic smog".
As noted earlier, corrosion products can completely break the contact
means through its increased volume, lock-up the connector so that it cannot
How can I achieve electrical contact improvement?
If a mated contact were potted in a clear material, sawn along at right-angles
to, the connection plane polished, and examined under a microscope, it
would be seen that what we think of as smooth contact surfaces are really
almost mountainous. As consequence, the contact area is far from continuous.
One of the benefits of gold plating in the days when gold was much less
expensive was derived from the fact that gold is soft and malleable. Under
the action of making the connection, the gold deformed, producing a much
larger total contact area. The plating, being thicker was much less likely
to be porous, and so corrosion was also prevented. In addition the closely
mated surface prevented the intrusion of oxygen and other contaminants.
At the present cost of gold, where gold is used, it is applied in as
thin a "flash" a possible consistent with low porosity. Even so, special
processes must be used to minimize this porosity as will be evident upon
reading almost any connector manufacturer's brochures.
Where gold is not used on both surfaces, the question becomes one of
the compatibility of the connecting surfaces both with one another and
with the intrusion environment. Often when less noble metals than gold
are used in a contact pair and combined with sufficiently high contact
pressure, they perform with greater reliability than gold to gold, or gold
to ? at lower pressure. The key here is to have enough pressure to exclude
oxygen and other contaminants.
Stabilant 22 (or either of its diluted form, Stabilant 22A
- isopropanol or Stabilant 22E - ethanol) when used on a contact
need only be present in a film thick enough to fill the interstices (or
gaps) between the contact surfaces. Because of its switching ability, it
will become conductive across these minute gaps without becoming conductive
between adjacent pains or causing leakage across insulating surfaces.
The conductivity of a new connector will not be substantially
improved by the Stabilant for the reason that there will probably
be a sufficient contact-area already. Thus any added contact-area (aided
by a material which has a higher volume resistance than the contacting
metal) will be of minor consequence. However the Stabilant's presence
will help to exclude oxygen and corrosive materials from the contacts,
and its surfactant action will keep existing contaminants in suspension.
The action of Stabilant on an aging or older contact is somewhat
different. Here the contact will not be as good; thus the conductivity
of the Stabilant (once switched on) will appreciably lower any contact
On high current applications, the lowered resistance well may be enough
to stop thermal runaway of the contact means, a situation where the heating
of a joint causes expansion which by stretching the clamping means beyond
their elastic limit results in a reduced contact pressure, increasing the
resistance of the contact area, and further increasing the heating. In
extreme cases this can literally cause a high current connector to explode.
Because of the "switching threshold effect", Stabilant
"switch" to a conductive state between adjacent contacts and its "off"
resistivity is high enough to prevent signal leakage.
Another potential problem in connectors is the area where the wire and
or cable is connected to the contact means. Frequently the wire may be
of solder or tin plated copper, while the rear of the contact body could
be anything from gold-plate, through silver or tin plate, to an as-machined
alloy. The introduction of solder itself on a bare copper wire can provide
a potential problem of galvanic corrosion while some of the fluxes themselves
can cause problems if they wick up into stranded wires. Then too there
is the possibility that breakdown products from the cable jacket can cause
corrosion of the copper.
Multiple point crimps, (made with properly designed tools) which insure
that there is sufficient pressure on the conductors to absolutely exclude
the entry of oxygen (and any contaminants as well) are often much more
reliable than soldered joints besides having greater consistency, The Stabilants
be used to enhance the operation of such joints.
What procedures can be followed on completed connectors?
Once a connector is assembled, it may be necessary to protect it against
the environment by somewhat (in the eyes of the connector manufacturer)
less orthodox mean One of the simplest of these is the use of a heat-shrinkable
polyolefin tubing with a internal low-molecular weight polyolefin (or equivalent)
material that literally melted when the outer tube layer is being shrunk.
This provides a much more intimate sea especially when the length is long
enough to stretch from the wire jacket over the connector and over the
connecting wire jacket. A problem with this material is that it looses
its elasticity and gets stiff at low temperatures.
Because the polyolefin material looses its resiliency at low temperatures,
leaks ma occur when its cold. We have seen this material used with rubber
splicing compound (as used on high voltage connections) where a single
layer of stretched splicing co pound is wrapped around the wire-connector-wire
area before the heat shrink tubing is used. The elasticity of the splicing
compound under compression is certainly better than that of any of the
heat shrinkable materials and the resultant "booted joint" much less messy
to open up.
A better method for environmental sealing to protect against the weather
(as practiced by the U.S. Navy) is as follows:
- A layer of ScotchTm 3M type 79 self-fusing tape wound with a 50% overlap
an stretched while being applied.
- A Layer of ScotchTm 3M type 33+ Vinyl tape wound with a 50% overlap an
stretched while being applied, followed by a similar layer wound in the
opposite direction. (also at a stretched - 50% overlap). 3) A sealant layer
of Scotchkotem Liquid Vinyl is applied overlap the layer of 33 tape. ScotchkoteTm
has a MEK solvent which melts into the surface of the 33+ tape to form
a continuous layer of vinyl material.
This type of sealant procedure can be applied over any type of connector
including heat-shrink boots to protect the polyolefin material against
UV rays), although in this latter case only the 33+ and Scotchkotem is
needed to provide a protective an flexible layer.
This and other solutions are, of course, designed to exclude the salt
and moisture from the connector and a choice of which treatment to use
will be based on the location of the connectors, the ease of application
of the treatment, and the life the materials used. Consideration must also
be given to possible degradation of he shrink materials themselves by ultraviolet,
ozone, or chemical contaminants.
What other uses are there for Stabilant materials in the marine/maritime field?
Mechanical switches in radios - digital, audio, RF, or high-voltage usage:
Typically a Radio consists of a transmitter/exciter, a RF power-amplifier,
and a receiver (possibly mounted separately), as well as high and low-voltage
power-supplies all which may be connected with multiple-pin plug and socket
connectors. These usually are often modular for ease of service and the
modules/cards may be, in turn, into connected with a combination of card-edge,
discreet card-connectors, as well as connectors which allow cards to be
stacked, wiring-harness-mounted connectors, coaxial RF connectors (either
discreet or modular) and header connectors just to mention few. The units
may also have manual or motor-driven rotary selector switches that carry
DC, AC or RF energy at many different levels. An area of significant failure
within HF, VHF, and UHF transmitters is the final amplifier switching circuits.
These often use relays and/or rotary switches. Failures are usually caused
by heating and conductivity erosion. The application of Stabilants to
all of these areas would improve the service life of the equipment and
reduce "resistance erosion with the concomitant increase in operational
One caveat; Where connectors operate under high-voltage conditions (such
as on some power-amplifier tubes) it is advisable to confine the Stabilant
areas to the actual contact surfaces.
RF connections - Interior and Exterior:
Radio-Frequency Coaxial and Waveguide connections operate in both dry-air
pressurized and un-pressurized (ambient-air) conditions. Stabilants
provide the appropriate protection for these connections.
RF wipers and Matrix RF power switches:
These applications provide switching for HF transmitter to Antenna
coupling connections. In some of these applications the control signals
are digitally multiplexed on the Coaxial cable center-conductor and the
matrix connection conductivity is critical, an obvious application for
Transmitter/Receiver switchboards on Military Ships:
Transmitter and receiver switchboards consist of rotary wafer-type
switches with typically 5 receiver or 20 transmitter positions and 2 receiver
to 12 transmitter poles of switches for each equipment position. Each patch
panel consists of 10 of these switch elements. In a typical large ship
installation, there may be over 4,000 individual switch wafers in the transmitter
patch panel alone. These are a common source of intermittent operational
problems. An obvious Stabilant application.
These include everything from navigational equipment to pilot lights
and comprise every imaginable sort of connection from microprocessors to
remote-compass readouts (not to forget engine instrumentation). Stabilants
reduce or eliminate problems here.
Miscellaneous Applications in the Marine Field:
These can cover everything from outboard-motor connections, flashlight
batteries, to emergency equipment and cameras. One often overlooked use
is the application of a minute amount of Stabilant to the micro-power
battery of a wristwatch or camera.
Quite literally, every electromechanical connection can benefit from
the use of the Stabilant family of materials.
In what forms is Stabilant available?
The Stabilants come in several common forms. The basic material
or concentrate is called Stabilant 22, while the isopropanol-diluted
form is designated Stabilant 22A. This is a 4:l dilution (by volume)
and is much easier to apply. (A third type is used for some military applications
where isopropyl alcohol cannot be used, This is Stabilant 22E, which
has an ethanol diluant. It is available on special order.) When used at
normal room temperatures or higher, the diluant will evaporate after the
application, leaving a thin film of the concentrate in place. In some applications
such as socketed IC's it is not even necessary to unplug the IC to treat
The dilute form should be used for treating existing crimp type joints
between multiple stranded wire and the contact.
What are the names of some of the materials that can be used to exclude
Heat Shrinkable tubing is manufactured by such companies as Alpha.
The surface irradiated type with the soft inner core is their type FIT-300
and FIT 321. The standard shrinkable polyolefin tubing is type FIT-221
and the 6:1 High-ratio is FIT 621