Marine Electrical Check List

A Guide to Inspecting Marine Electrical Systems

This document is available on the Internet at http://www.yachtdoctor.com/ and it is shareware.
copyright (c) 1990, 1996 by Robb Zuk, Salt Spring Island, Canada. All rights reserved.

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Contents

• Introduction
• Stray Current
• Common Earth Point
• Batteries
• Connections
• Wires & Cables
• Labelling & Diagrams
• Battery Switch
• Fuses, Breakers & Switches
• Bilge Pump System
• Alternator
• Starter
• Anchor Winch / Windlass
• Battery Isolator (charging diodes)
• Battery Charger
• 240 Volt AC System
• Meters
• Bonding and Lightning Protection
• Corrosion Protection
• Compass
• Electrical Interference (noise)
• Miscellaneous
• Pre-Cruise Mini Check List
  • Batteries
  • Wiring & Connections
  • Alternator, Starter & Winch Motor
  • Miscellaneous
  • Electrical System Spares
• References

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Introduction

This document is an explanatory guide for checking marine electrical systems. There are some good, detailed publications on this subject and I recommend them for additional reading when you have the time...

For now, this check list will get you started with a minimum of reading. I summarised points from Canadian, American and British marine wiring regulations. However, I did not quote these publications exhaustively so don't consider Marine Electrical Check List a legal document.

Before working on your system, clarify any confusing points with a professional electrician.

Researching and writing this document took several months of my time -- I offer it on the Internet as shareware. If you read it and use it, please send US$10 to:

Robb Zuk
Box 225 Ganges PO
Salt Spring, BC V8K 2V9
CANADA

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Stray Current (an explanation)

Stray current is electricity that is flowing where it's not supposed to -- through water, fittings on your boat, wet wood, damp surfaces, etc. It can be a shock hazard and it can cause corrosion (technically known as electrolytic corrosion). Stray current corrosion is caused by a power source such as your batteries or the shore power connection. It is unlikely for serious corrosion to be caused by stray currents flowing through the water, without a metallic path to your boat. Because of the relatively high driving voltages, stray current corrosion can act far more quickly than the corrosion caused by dissimilar metals in contact (galvanic corrosion).

Note: The word electrolysis is often mistakenly used to describe various kinds of corrosion. Electrolysis actually refers to the bubbling off of gases that occurs with electrolytic corrosion.

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Common Earth Point (ship's earth)

• earths from batteries, engine, switch-panel negative bus bar, bonding system, auxiliary power generator, underwater earth plate, ship's 240 Volt safety-earth, and GPS signal earth all meet at one point
  
  This point must be a heavy bus bar or bracket with bolted connections.
  
  Note: When referring to 12 Volt wiring, 'earth', 'negative' and 'earth return' are all equivalent terms.

• easy to access and located as far above bilge levels as practicable

• labelled as Common Earth Point

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Batteries

WARNING! The hydrogen gas in and around lead-acid batteries is explosive and the acid can burn skin and eyes. Avoid sparks and wash well after handling your battery.

• acid (electrolyte) level is up to plastic liner inside holes
  
  Letting the acid level go below the top of the plates will kill a battery quickly. Use distilled water to top up batteries. If distilled water isn't available, tap water is OK if it's clear, not 'hard,' and not highly chlorinated. Let the cold tap run for a minute to clear metal ions out of the pipes and use a well rinsed, glass or plastic container to transfer.

• fully charged specific gravity is 1.245 to 1.300 in each cell

• In a partially discharged battery, specific gravity of each cell does not vary by more than 0.050 from the other cells
  
  Battery cells sometimes charge with uneven specific gravities but after discharging about 25% (from a full charge) they should even out.
  
  Note: If it's been a while since charging the battery, acid may have settled to the bottom leaving a lower specific gravity electrolyte on the surface. If you overfilled the battery then the electrolyte may be diluted. Either of these situations can result in abnormally low readings and they don't necessarily indicate a weak battery cell.

• 'at rest' battery voltage is 12.1 to 12.8 Volts
  
  A battery is 'at rest' when it isn't being used and hasn't received a charging current for at least 12 hours. A voltage above 12.8 Volts indicates that the battery is still settling after a charge. A voltage below 12.1 Volts indicates either a weak cell or a battery charge below 50% of capacity.
  
  Note: Standard batteries have their life span shortened drastically by deep discharges, even to the 50% level. True deep cycle batteries (see below) function well with 50% discharges.

• engine cranks properly for 5 seconds with each battery alone -- battery voltage is above 9.5 Volts and steady while cranking
  
  Perform this test only after engine has been running so that protective oil has circulated. Disconnect coil '+' wire or engage diesel fuel shut-off mechanism to keep engine from starting. It's possible for batteries to fail this high current test while still being able to provide good storage capacity at lower currents.
  
  Note: If engine doesn't crank properly and battery voltage remains high, then there is a problem with the starting circuit or starter motor.
  
  Note: Starter or electric winch motors will normally 'pull' a battery's voltage down to 9 or 10 Volts while they're operating. The battery should recover most of its 'at rest' voltage within seconds.

• batteries draw not more than a few amps of charging current once they are charged

• except during conditioning (see below), water loss is at most a few ounces (50 to 100 ml) per cell, per year
  
  Significant water loss indicates a problem. If the water loss occurs evenly in the cells, alternator or battery charger voltages may be too high. Water loss in only one or two cells indicates weak or shorted cells.

• batteries are true deep cycle type if used for anything but starting
  
  Specify that you want 'golf caddy' batteries because most marine 'deep cycle' batteries are only marginally better than automotive batteries for deep cycling. True deep cycle batteries will provide many hundreds of charge/discharge cycles instead of only a few dozen.
  
  Note: Avoid discharging deep cycle batteries below 50% of their capacity. A 50% discharged battery has an 'at rest' voltage (see above) of 12.1 to 12.2 Volts.

• top surfaces clean and dry

• cables in good condition -- ends are soldered and correct size for terminal connectors
  
  Check cables for broken or corroded strands, especially at the ends.

• only one cable to each terminal
  
  In particular, avoid small wires in battery compartment. Run them to the battery switch and switch-panel negative bus bar instead.

• no connection depends on spring tension (i.e., no crocodile clips)

• connections cleaned and sealed

• positive terminals have insulating cover

• negative cables go directly to Common Earth Point
  
  Many systems have the negative cable running directly to the engine as part of the starting circuit. This means that other negative connections need to be at the engine, or in the battery box, which can cause corrosion problems.

• positive cables go directly to nearby battery switch

• no batteries wired in parallel
  
  Paralleled batteries tend to fight each other when they are at rest -- this causes premature discharge and a shortened life span. It's OK to parallel batteries temporarily with the battery switch, while charging, starting and running the engine -- just avoid leaving the switch on 'BOTH' when no power is being drawn. If you require a large battery capacity, connect several 6 Volt or even 2 Volt cells in series instead of wiring 12 Volt cells in parallel.
  
  Note: Two batteries are in parallel if their positive terminals are connected and their negative terminals are connected.

• ventilation is provided for cooling and for venting the gases produced by batteries
  
  Batteries produce hydrogen, oxygen and corrosive sulphide gases. The lighter-than-air hydrogen must be able to rise naturally through a venting system, with or without a blower.

• batteries can be conditioned with an equalizing current
  
  After a normal full charge, conditioning consists of applying a reduced charging current (2 to 5 amps for most batteries) either for a few hours or until battery voltage rises to 15.5 - 16.5 Volts -- this takes the lead sulphate 'crust' off the battery plates and helps maintain full storage capacity. Check the acid level when finished because this process causes bubbling and fluid loss. Condition batteries every month when they're being used heavily. Conditioning requires either an override on the alternator's standard voltage regulator or a battery charger with a conditioning or 'equalising' option.
  
  Note: Don't condition batteries when they are in parallel or one battery may take most of the conditioning current.
  
  Note: Shut off all electronic equipment during conditioning because of the high battery voltage.

• inlet vent below batteries

• outlet vent as high as possible in battery compartment

• if using an electric blower for battery venting, the motor is not in the air stream

• ventilation system is for batteries only

• batteries strapped down and prevented from shifting

• battery compartment protected against acid spills

• easy to access and located as high above bilge as practicable

• if batteries are not being used, they are given a full charge at least once every 3 months
  
  Lead acid batteries will self-discharge over a period of months so they should be charged periodically to ensure that they don't completely discharge. This is especially important during freezing weather because a discharged battery can freeze develop cracks in the case.

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Connections

• all easily accessible and above bilge water levels
  
  If you must make a connection in a poorly accessible spot, solder it and seal it against moisture.

• soldered joints are first mechanically connected (crimped, bolted or twisted) -- crimped or twisted connections are soldered as well
  
  Connections held by solder alone will fracture with little stress. Some commercially crimped connections may be OK without soldering but most are fallible in a marine environment. Make sure solder is rosin core (60/40), not acid core.

• mechanical connections are strong (nut and bolt/stud, or machine screw into tapped metal)
  
  Self-tapping screws into GRP, wood, or thin sheet metal don't provide the consistent high pressure required for a reliable gas-tight (safe from humid air) mechanical connection.
  
  Note: If you must use bare wire in a mechanical connection, solder the end of the wire first. Wire strands that are 'crushed' in a connector are very susceptible to vibration breakage.

• contact surfaces of mechanical connections are clean and coated with moisture resisting sealant before being put together
  
  Note: Sealant does not need to conduct electricity. When you force two clean and sealed metal surfaces together with enough pressure, high spots in the metals press against each other and force the sealant aside. In this way, metal-to-metal contacts occur all across a connection, with 'doughnuts' of sealant surrounding each contact area. Use petroleum jelly (Vaseline), water resistant grease, special contact lubricant such as Electrolube for sealant. When sealing light bulb bases, replaceable fuses and other friction connections, 'rock' the connection back and forth a few times to create good metal to metal contact while squeezing the sealant aside. Applying sealant to the exterior of existing connections will help prevent deterioration but may not last long. By sealing the interior surfaces of a connection before you put it together, you get a long lasting barrier to the moist marine environment

  Note: DO NOT use silicone grease on electrical connections as it will form a thin non-conducting, glassy polyoxysilane film after an indeterminate time.

• mechanical connections are locked
  
  'Star' lock washers are best for bolted/screwed connections because they dig into the metal surfaces, providing good metal to metal contact.

• no connections made with twist-on wire nuts (Marrettes)
  
  If you insulate a soldered connection with a twist-on wire nut, turn it up so that water can't collect in it.

• terminal connectors are ring type and correct size -- they are not 'forked' or spade connectors
  
  Ring type connectors hold best if a wire is accidentally pulled or a connection becomes loose. Avoid spade or other 'push on, pull off' connectors if possible. If you do use spade connectors, they must be clean and sealed, provide solid mechanical contact, be positioned so that water cannot collect in the connection, and be anchored to protect against accidental pulling on the wires. A better option is to install a terminal strip so that you can make ring terminal connections. Seal these connections as well.

• terminal strips are easy to clean type (not enclosed), with covers

• terminal strip uses minimum size No. 8 screws
  
  Stripped threads are likely on smaller sizes.

• all connections that are at a voltage different from the Common Earth Point (i.e., all positive or 'live' connections) are insulated with heat-shrink sleeving or rubber boots
  
  Electrical tape does not hold up well in a marine environment. However, if tape is used for moisture sealing or to insulate an awkwardly shaped connection, secure the finishing end with a cable tie or cover as much of the tape as possible with heat-shrink sleeving to keep it from unravelling.

• wires anchored next to connections for strain relief
  
  In places where wire vibration or movement is unavoidable (e.g., some engine and bonding wires) make sure that only unsoldered, uncrimped wire is moving. This may require heavy duty connectors and heat-shrink sleeving on the wire next to connectors. In these situations, leave a little extra wire in a loose coil so that movement of any given section of wire is minimised and there is no chance of the wire being pulled taught.

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Wires & Cables (conductors)

• 12 Volt system is all 'two wire' type
  
  All devices have insulated, positive and negative wires running to them. The hull or bonding system must not be used for the earth because of potential corrosion problems.

• all wiring is stranded (no solid wire)
  
  Solid wire is more susceptible to vibration breakage than stranded wire. However, very finely stranded wire is likely to suffer corrosion problems so it should also be avoided.

• routed as high above bilge water levels as practicable

• conductors not kinked or bent sharply
  
  Sharp bends will fatigue metal which eventually can cause fracturing.

• insulation is flame retardant and moisture resistant -- in bilge and engine compartment, it is oil resistant as well

• all wires have a flame retardant, moisture resistant (and oil resistant, as above) protective sheath over their insulation for the full length of the wire, except at the ends

• no frayed or cracked insulation
  
  The engine compartment and bilge is a likely area to have faulty insulation.

• wires are appropriate gauge for current being drawn and minimum size is 1.25 mm2 (16 AWG)
  
  Small wires break easily.

• 12 Volt system leaks less than 5 mA of current (test)
  
  With all circuits off and the battery switch off, connect a sensitive ammeter or LED indicator light across the battery switch contacts to indicate current leakage. Bilge pumps and their float switches are often a trouble spot so check this circuit as well if it bypasses the battery switch.

• supported at intervals of not more than 45 cm (18") unless running in bottom of conduit or trough -- supporting clips are screwed down, not nailed
  
  Wiring must not be able to move or flex with boat vibrations.

• if wiring is in conduit or troughs, drain holes exist to prevent collection of water

• protected from mechanical damage in exposed areas

• protected from chafing where passing through bulkheads, junction boxes, or other holes

• minimum of splices -- unavoidable splices are soldered and sealed from moisture

• wires approach terminals and devices from below (use drip loops if necessary)
  
  Water that may run along wiring must not be able to wet connections or devices.

• wire colour coding is not opposed to standards and is consistent throughout the system
  
  3-conductor AC wiring should have: live/brown, neutral/blue, and earth/green/yellow. DC standards are: positive/red or colour coded as to purpose, and negative/black.

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Labelling & Diagrams

• every wire labelled at both ends
  
  Label with descriptive words for ease of trouble shooting and modification -- colour coding is often obscured by paint and numbering requires the use of schematics. Tags can be made from white, marine-vinyl and marked with an indelible, fine black felt pen. Attach the labels with plastic cable ties. If using tape on numbers, cover them with clear heat-shrink sleeving since tape is unreliable in marine environments.

• every electrical system is documented in diagrams or schematics and these indicate colour, relative size and labelling of wiring

• all diagrams, information sheets, operating manuals, etc. in one location on board

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Battery Switch ('master' or 'main' battery switch)

• ignition protected (enclosed) and marine rated

• easily accessible for use and maintenance

• interrupts positive cables from batteries

• located near batteries

• switches off all systems except bilge pump circuit and possibly entry alarm or electronic memories

• connections clean and sealed

• for each 'On' position, voltage drop is less than 0.5 Volts in switch while engine is cranking
  
  This is a test of resistance in the switch.

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Fuses, Contact breakers & Switches

• all circuits are fuse or contact breaker protected
  
  The only exception to this may be the starter motor circuit.

• in 12 Volt system all fuses, contact breakers and switches in positive side of circuits
  
  Breaking the negative side of a circuit can cause stray current corrosion.

• contact breakers are trip free type (cannot be overridden)

• fuses or contact breakers rated not more than rating of the smallest wiring they protect

• electric motor fuses or contact breakers rated not more than 125% of maximum motor load

• no auto-resetting contact breakers (e.g., thermal cut-out contact breakers) unless circuit is already protected by fuse or manually reset contact breaker

• all fuses or contact breakers are located in switch-panel except, perhaps, main fuse or contact breaker
  
  If a fuse or contact breaker can't be in a switch-panel, it must be in the battery end of the circuit. In-line fuses should be avoided unless they're providing extra protection for a device on a shared circuit. They must be very accessible and the protected end of the fuse holder should connect to the positive wire coming from the battery.

• in 12 Volt system, main positive conductor to switch-panel is fuse or contact breaker protected as near to battery end of conductor as practicable

• fuses have clean, tight, sealed contacts

• switch-panel's wiring easily accessed for maintenance

• switch-panel ventilated

• switch-panel compartment and junction boxes not flammable and not metal

• all switches labelled

• if engine is petrol powered, switches in engine and fuel tank compartments are ignition protected and approved

• switches in head, cockpit and other moist areas have rubber covers for moisture protection

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Bilge Pump System

• wiring runs above bilge water levels where possible

• float switch is protected from being jammed open by debris

• there is a high-volume, manually-operated emergency pump

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Alternator

• with engine running, batteries fully charged and a 1 or 2 Amp load on system (a light turned on), voltage to batteries is 13.9 to 14.4 Volts -- voltage remains constant as more loads are turned on, up to the rated output of the alternator
  
  With constant voltage regulators (most common), a high voltage setting will slowly fry the batteries unless the engine is used very little. A low voltage setting causes slow charging.
  
  Note: Most voltage regulators can be overridden with additional circuitry to provide fast charging while at anchor, or to condition batteries. The override circuitry can be as simple as a switched resistor or using an automatic alternator regulator.

• IF it has earth terminal, a heavy wire connects it to the Common Earth Point or engine block
  ALTERNATIVELY: connection between alternator housing and engine block clean and sealed
  
  When an alternator doesn't have a separate earth terminal, the negative connection is made between the alternator housing and the engine block. This connection must then be treated the same as any other electrical connection.

• alternator field cut-off switch on battery switch
  OR: voltage transient suppresser on output
  OR: battery isolator/charging diodes in alternator output
  
  Any of these devices will protect the alternator if the battery switch is accidentally shut off while the engine is running.

• power to the voltage regulator supplied through an oil pressure switch unless supplied internally from alternator
  
  Some regulators are powered directly from the ignition switch. This means the engine is loaded down by the alternator even before protective oil has circulated. It's better for the engine to have the alternator turn on after oil pressure has built up.

• voltage regulator is external to alternator
  
  Some voltage regulators are located inside the alternator housing. This makes repair or replacement a time consuming job.

• brushes and slip rings clean and in good condition

• bearings in good condition

• external connections clean and sealed

• drive belt(s) tight and in good condition
  
  Note: Good quality, toothed V-belts last longer and are more efficient than solid V-belts because less heat builds up in the belt.

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Starter

• IF starter motor has earth terminal, a heavy cable connects it to the Common Earth Point or engine block
  ALTERNATIVELY: connection between starter frame and engine block clean and sealed
  
  Since starting currents are so high, good connections are crucial. Run the engine earth cable directly to the starter's mounting bolts or to the starter's earth terminal if it has one.

• brushes and commutator clean and not too worn

• bearings/bushings in good condition

• solenoid plunger clean and lubricated

• solenoid internal contacts clean and not pitted
  
  High current arcing between the solenoid's main contact surfaces makes them subject to pitting and therefore poor electrical contact.

• external connections clean and sealed

• starter motor gets 9.0 Volts or more while cranking engine
  
  This is a test of batteries, cables, connections and solenoid.

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Anchor Winch / Windlass

• fuse or 'trip free' (cannot be overridden) contact breaker located in positive cable near batteries

• main current switching done through a solenoid
  
  Remote mounted starter solenoids are suitable. Many momentary switches are not rated for the high current drawn by winch motors or the arcing caused by such a large inductive load. Pitting in the contact surfaces can cause the switch to 'stick' and leave you with a runaway winch...

• brushes and commutator clean and not too worn

• bearings/bushings in good condition

• connections sealed and protected from anchor chain or line

• electric motor gets 9.0 Volts or more when running under load
  
  This is a test of batteries, cables, connections and switches/solenoids.

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Battery Isolator (charging diodes)

• alternator output voltage is raised to compensate for the voltage drop in charging diodes unless the diodes are connected across battery switch
  
  Charging diodes lower the voltage received by the batteries. If this is not accounted for, charging will occur too slowly.
  
  Note: If the diodes connect ACROSS battery switch, DON'T adjust the alternator output. In this case, the switch bypasses the diodes when it is 'on' -- no diode voltage drop occurs and the batteries charge normally.

• good ventilation for cooling
  
  Charging diodes can generate a lot of heat
  
  Note: Battery isolators or charging diodes only isolate batteries from each other in the alternator or charger circuit. The batteries are NOT isolated when the battery switch is on 'ALL.' To avoid the problem of paralleled batteries discharging and harming each other, the battery switch should be on 'ALL' only while starting or running the engine.

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Battery Charger

• 240 Volt side electrically isolated from 12 Volt side (test at 240 VAC if qualified)

• ammeter to indicate output

• overload protection on output

• charger shuts off completely or drops to 13.0 - 13.2 Volts (float voltage) after charging batteries
  
  Float voltages of 13.8 Volts or more are common and these will eventually fry your batteries. If the charger doesn't have a proper float voltage, leave it off except when you need it. It's far better to leave batteries alone, and give them a charge every few months, than to have them at a high float voltage. If you must leave a charger turned on, (e.g., with fridges or heavily used bilge pumps), make sure it has a proper float voltage.

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240 Volt AC System

WARNING! 240 Volt systems can be dangerous, especially in marine environments. Don't use your system if you have any doubts about its safety. Don't work on your system if you are unsure of what you're doing.

Following are two key points to a safe 240 Volt system:

1. The live (brown), neutral (blue) and safety-earth (green/yellow) wires must be intact and not mixed up (see AC System Warning Device, below).

2. All current must flow in the live and neutral wires only. Current flowing anywhere else is 'stray', a fault condition and presents a shock and corrosion hazard. RCD's (Residual Current Device) sometimes called a Residual Current Circuit Breaker (RCCB) or Earth Leakage Circuit Breaker (ELCB) or Ground Fault Circuit Interrupter (GFCI) in the USA ensure or an isolation transformer ensures that current flows only in the live and neutral wires. RCD's trip if they detect a loss of current from the live or neutral wire. Isolation transformers allow current to flow only in the live and neutral wires

Note: No safety system protects against shock if you touch both live and neutral wires at the same time. By touching both wires, you are no different from a light bulb or toaster since you are actually in the live and neutral circuit. This can be fatal! Luckily, most fault conditions occur when current is able to flow outside of the live and neutral circuit. This is the situation that RCDs and isolation transformers protect against.

• ship to shore plug connector has a locking cover and is insulated from the hull with a rubber gasket

• ganged, double-pole main contact breaker is the first part of ship's system and it is easily accessible
  
  The main contact breaker must disconnect both live (brown) and neutral (blue) wires simultaneously.

• main contact breaker rating is appropriate for ship to shore plug connector and wiring used

• all power indicating devices are wired to live (brown) and neutral (blue) wires only unless switched by a 'momentary on' switch
  
  For example, reverse polarity (live and neutral reversed) detectors are wired between neutral and safety earth or ship's earth. If the detector is permanently wired into the circuit, it can cause stray current corrosion by allowing current to flow in the safety-earths or through the bonding system.
  
  Note: A momentary switch is not required if the device uses circuitry to keep it from drawing more than 1 mA in safety-earths, ship's earth, or bonding system.

• AC system warning device is testable and indicates reverse polarity, open safety-earth, live on earth, etc. (all are dangerous conditions)
  
  Note: Unless your AC safety indicating system is quite sophisticated, it is a good idea to have a plug-in AC socket outlet tester. They cost £8 to £10 and test most dangerous conditions with their 3 lights. Do not leave this tester plugged in because it causes current to flow in the safety-earth, which is a cause of stray current corrosion.

• no connection from either live (brown) or neutral (blue) wires to any part of 12 Volt system, including bonding system (test at 240 VAC if qualified)
  
  A connection between 240 Volt AC live or neutral wires and the 12 Volt system would be potentially dangerous and could cause stray current corrosion. This problem can occur with AC appliances, such as battery chargers or live water heaters, and with poor insulation, wet connections, or broken wires.

• wiring is stranded 3-conductor and is 2.5 mm2 (14 AWG) minimum

• ends of bare wires are soldered before screw connecting
  
  Bare stranded wire will break easily if it is 'crushed' under a screw head.

• all connections (especially 'live' ones) in switch-panel or other accessible areas are insulated
  
  Many commercially available panels contain both AC and DC systems, with all terminals exposed. The 240 Volt terminals must be insulated for safety.

• all connections are accessible only with the use of tools
  
  We wouldn't want tiny exploring hands endangering themselves would we?

• all switches, fuses and contact breakers disrupt the live (brown) wire
  
  Contact breakers may be the ganged, double-pole type, which disrupts both live (brown) and neutral (blue) wires simultaneously. The neutral wire must not be broken while the live wire is intact.

• no fuses, contact breakers, or switches in safety-earth (green/yellow)

• outlets in head and galley are protected by a RCD (Residual Current Device)
  
  Most regulatory bodies require RCD protection in heads and galleys since they tend to be especially wet spaces. However, since boats can be wet all over I highly recommended that RCDs or an isolation transformer be installed to protect the entire 240 Volt system.

• all 240 Volt socket outlets are 3 pin, earthing type and are incompatible with 12 Volt DC outlets

• outlet faces clean and terminals coated with a moisture resistant sealant such as petroleum jelly
  
  240 Volt AC current leakage is likely with dirty or moist outlets. This leakage can cause RCD devices to trip and, in extreme cases, can cause stray current corrosion or be a shock hazard.

• if there's an on board 240 Volt AC power source (generator or inverter) wired into the system, there is a DPDT (double-pole, double-throw) switch in the live (brown) and neutral (blue) wires that switches the system between shore power and ship's AC power source
  
  Shore power and the ship's AC power source must not connect to each other or sparks can fly!

• all wiring enters its destination from below (or in a way that won't allow water drips to enter)

• AC system is one of the following three types:

1. Fully RCD protected:
   • all circuits protected by RCD (Residual Current Device) devices
     
     RCDs are available as both circuit contact breakers and socket outlets. RCD socket outlets must be in a circuit already protected by a circuit contact breaker (usually 20 Amp maximum) they do not function as an overload protector. RCD socket outlets can be wired to protect the rest of the circuit, continuing from that socket outlet. RCD devices must have a test feature and they should be tested monthly to ensure safety and corrosion protection.
     
     Note: The entire AC system could be protected by a single RCD main contact breaker. However, this is not advisable if you have many AC circuits because the combined leakage of all AC devices could trip the RCD unnecessarily. For large systems each circuit should have its own RCD device.

   • shore safety-earth (green/yellow) continues as far as first RCD device, stops there and does not connect to anything at that point

   • ship's safety-earth (green/yellow) starts at the first RCD device, connects to RCD and its box and continues from there

   • ship's safety-earth is connected to Common Earth Point

   • no connection from shore safety-earth to Common Earth Point (test at 240 VAC if qualified)
     
     The connection from shore safety-earth to ship's earth can allow stray current corrosion. This connection is safely avoided only with complete RCD protection or an isolation transformer system.
   
   
2. Isolation transformer protected:
   • all AC current supplied through an isolation transformer located between main contact breaker and switch-panel
     
     The transformer should be marine rated and large enough to supply all circuits used on board.

   • if neither secondary wires (ship side of transformer) are earthed to Common Earth Point, all circuit contact breakers are ganged, double-pole type

   • shore safety-earth (green/yellow) connected to isolation transformer case only

   • ship's safety-earth (green/yellow) connected to Common Earth Point

   • no connection from shore safety-earth to Common Earth Point (test at 240 VAC if qualified)
     
     The connection from shore safety-earth to ship's earth can allow stray current corrosion. This connection is safely avoided only with complete RCD protection or an isolation transformer system.
     
     Note: RCDs are not required with a correctly operating isolation transformer but may be added as protection against a malfunctioning transformer.
   
   
3. Incomplete RCDs, no isolation:
   • missing or incomplete RCD (Residual Current Device) protection and no isolation transformer

   • AC safety-earths (green/yellow) from shore and ship are connected together and to Common Earth Point
     
     In this system, the connection between ship and shore safety earths, and ship's earth is critical for protection against shock hazard and stray current corrosion. This connection does not protect against someone touching the live (brown) wire directly while in contact with bilge, sea, or bonding system. A RCD or isolation transformer system would protect in this case.
     
     Note: Connecting the ship's safety-earth to ship's earth only, or to shore safety-earth only, can create a shock and corrosion hazard in this system.
     
     Note: Without complete RCD or isolation transformer protection, the safety-earth system must be solid on boat and shore to get the protection it can provide. While this 240 Volt AC system is common, it provides limited safety protection and allows several kinds of stray current corrosion to occur since your boat's underwater metal parts are electrically connected to other boats and to the shore system earth. DC stray current can be blocked with a 'galvanic isolator' (diode or capacitor type) connected in series with the safety-earth wire. However, high voltage AC stray current cannot be blocked safely. For these reasons, the full RCD or isolation transformer systems (No. 1 and No. 2 above), which safely eliminate the shore safety-earth to ship's earth connection, are highly recommended.

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Meters

• DC voltmeter can be read to nearest 0.1 Volt
  
  A voltmeter allows monitoring of alternator and charger operation. A sensitive voltmeter will also indicate storage capacity remaining in batteries.

• DC ammeter showing alternator output
  
  An ammeter is usually part of engine instrumentation. It allows monitoring of alternator operation.

• DC ammeter indicating power drawn from batteries
  
  An ammeter for the switch-panel can indicate faults in individual circuits. The meter's resolution should be better than 1 Amp (.01 Amp or 1 mA resolution is best). An indicator light for small current leaks is desirable and simple to install.
  
  Note: The connections on DC ammeters (or their shunts) carry full current so they must be clean, sealed and locked.

• AC voltmeter and ammeter in system if shore power used extensively or if there's an on board AC generator (alternator)
  
  AC meters show the status of shore power or generating system and can indicate faults in the ship's AC system.

Note: A meter can be installed to monitor the functioning of your zinc anode, anti-corrosion system.

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Bonding and Lightning Protection

Four reasons for a bonding system are:

1. Electrically connect metal fittings for corrosion protection systems.
2. Protect metal fittings from stray currents originating on board.
3. Reduce electronic interference (noise) for GPS and radios.
4. Provide a safe path for lightning strikes and the high voltages induced in metal objects by a lightning strike.

• system uses heavy conductors -- minimum size is 8.5 mm2 (8 AWG) wire or 1 mm x 10 mm (1/32" x 1/2") copper or bronze bar
  
  Some sources recommend a heavier conductor (up to 65 mm2 (2/0 AWG) for the main lightning path which is down the mast, along the main bonding conductor, and out to the shaft and prop and/or underwater earthing plate.

• all connections above normal bilge water levels

• all connections accessible, clean, bolted and soldered or sealed
  
  Soldered connections must first be well connected mechanically since solder is weak. Also, solder can melt with the high current of a lightening strike.

• conductors are run with no sharp kinks or bends
  
  Sharp bends will fatigue metal and can eventually cause fracturing.

• conductors run separate from other wiring as much as practicable
  
  The high current of a lightning strike can cause equipment damaging voltages to be induced in nearby wiring.

• insulation (optional) is green or yellow
  
  Note: This system is separate from the 240 Volt safety-earths which may also be green.

• does not normally carry current (except for corrosion protection current)
  
  Do not use the bonding system in place of negative power wires (i.e., as a 'earth return') or stray current corrosion problems can result.

• the 'main bonding conductor' runs near the centre line of the ship and connects to the Common Earth Point -- all other bonding conductors connect to the main bonding conductor or directly to the Common Earth Point
  
  Running bonding conductors from one fitting to another increases the risk of shock and corrosion damage if stray currents run through the bonding system. Each bonded fitting should have only one connection point and one wire running to it.

• bonding system connects with DC power system at Common Earth Point only (test)

• The following connections exist to reduce the danger from stray currents originating on board:
  
  Note: These connections also provide the basis for hull-mounted zinc anode or impressed-current corrosion protection systems and are part of the lightning protection system.
  • rudder shaft (if not mild steel) to main bonding conductor

  • trim tabs to main bonding conductor

  • propeller and shaft to main bonding conductor via wiper on shaft
    
    The prop shaft wiper provides a path for corrosion protection current. It also allows lightning strikes to earth through the propeller (at least one square foot of underwater metal is required). Make sure that wiper is on the propeller side of any non-conducting, flexible shaft couplers or install a jumper wire over the shaft coupler.
    
    Note: Electrical contact through lubricated gears and bearings is unreliable. Therefore, the engine block connection must not be counted on to connect the propeller and shaft to the bonding system.

  • shaft support strut/bracket (if not mild steel) to main bonding conductor

  • metal through-hull fittings to main bonding conductor
    
    Through-hull fittings that are electrically isolated, in little danger of stray current corrosion and remote from protective zinc anodes, need not be bonded (fittings that are far away from your zinc anodes are not protected anyway). Keeping these fittings unbonded is desirable since a large system is more likely to pick up stray currents flowing through the water.

  • if equipped with underwater earth plate, it is connected to Common Earth Point

  • engine block to Common Earth Point
    
    The engine block is often connected to the Common Earth Point as part of the starting circuit.

  • other metal components, that are exposed to water and require protection from corrosion or stray currents, are connected to the main bonding conductor.
    
    Note: Underwater metals that are widely separated in the Galvanic series (e.g., mild steel and stainless steel) must not be electrically connected. For example, a mild steel rudder should have its own attached zinc anode and must not be connected to a bonding system containing bronzes or stainless steel. Otherwise, the brasses and stainless steels will be over-protected, causing wasted battery power or a shortened zinc anode life span and possible alkali rot in wood hulls. Also, if the corrosion protection system were to fail, the mild steel would be attacked by the more noble brasses and stainless steels. With zinc anode or impressed-current protection, bronze, stainless steel, monel, lead and some other alloys are compatible.

• The following connections exist for lightning protection:
  • each piece of metal standing rigging (stays and shrouds) to main bonding conductor

  • if mast is metal, mast base to main bonding conductor

  • if mast is not metal, a copper spike extends 15 cm (6") above top of mast and a conductor runs from the spike down mast to main bonding conductor
    
    If lightning does not have a metallic path to the sea, it can travel through wood or you causing serious damage.

  • if equipped with masthead aerial, it is a metal whip on a base loading coil and it is well connected to mast or mast conductor
    
    Various kinds of lightning arresters are available to provide protection for aerial cables and radios.

  • all metal parts of fuel system (tanks, lines, electric pumps, valves and fill fittings) to main bonding conductor

  • metal water and holding tanks and their fill hardware on deck to main bonding conductor

  • large or long metallic items (steering and engine control cables, sail tracks, stanchions and life lines, pulpit, cockpit railing, stove, chimneys, sinks, metal cabinets, etc.) to main bonding conductor
    

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Corrosion Protection

• if hull is wood, all fasteners are same type of metal
  
  In wet wood, different metals that are near to each other can cause galvanic corrosion to the less noble metal (zinc is one of the least noble metals). For example, galvanised fasteners would have a shortened life if bronze fasteners were nearby.

• galvanized fasteners used underwater are hot-dipped type
  
  Zinc plated fasteners will rust quite quickly because the protective plating is not very thick compared to a hot-dipped zinc coating.

• fasteners or fittings that are exposed to water are not made of brass, naval bronze, or manganese bronze
  
  These metals have a high zinc content and will corrode severely due to 'dezincification.' Most true bronzes (silicon, aluminium, or phosphor bronze) are OK under water, provided they aren't in contact with incompatible metals.
  
  Note: Do not use household-plumbing type gate valves in salt water systems because they are usually made of brass.
  
  Note: Propellers and shafts are sometimes made of brass or manganese bronze. Dezincification of these fittings can be slowed down with zinc anode or impressed-current protection systems.

• fasteners are same metal as fittings, or slightly more noble than fitting
  
  Note: Skin fittings are a particular problem area for underwater corrosion. Skin fittings and their fasteners should both be made of a true bronze.

• no copper in areas of fast moving water (e.g., exhaust elbows)
  
  Copper corrodes very little in still water but suffers from impingement attack (a type of corrosion) in fast moving water.

• no copper alloys (brass, bronze, etc.) within 60 cm (2 ft) of aluminium outdrive
  
  Underwater aluminium can corrode severely in the vicinity of copper so existing copper alloy parts should be painted with epoxy paint to help minimise their impact.

• no electrical path from underwater aluminium to any other underwater metals (test)
  
  Underwater aluminium will galvanically corrode when electrically connected to most other underwater metals. Magnesium and zinc are exceptions that can be used to protect aluminium.

• aluminium masts, outdrives or other fittings exposed to the weather use stainless steel fasteners and are in contact with no metals other than aluminium, stainless steel, galvanised steel, or monel
  
  Copper and copper alloys such as brass and bronze must not be joined to aluminium that is exposed to the weather because of the vigorous galvanic corrosion that they can cause. Stainless steel is much more noble (further from zinc) than aluminium but it develops a protective oxide coating so corrosion of the aluminium is minimal. Also, the corrosive effects of a small stainless fastener are spread out over a relatively large area of the aluminium fitting and so it will do little concentrated damage.

• hot-dipped zinc or galvanised metals (chains, anchors, etc.) in contact with galvanised, hot-dipped, or mild steel metals only
  
  Severe corrosion can result from mixing these metals incorrectly. Do not use galvanised chain on a stainless steel anchor, stainless shackles on galvanised chain, or stainless wire on a galvanised shackle, etc.

• stainless steel used with caution underwater
  
  Stainless is good underwater except when oxygen is not available to its surface, as happens under marine growth, in wet wood, inside stuffing blocks and rubber bearings, and underneath fittings. When stainless is in these common situations, deep pitting (crevice corrosion) of the metal can occur and structural failure can result. If stainless components are used underwater, they must be well bedded in waterproof 'mastic' to exclude moisture from underneath the fitting and they should be inspected annually to check for pitting. Stainless fasteners in damp wood are particularly prone to crevice corrosion and should definitely be avoided. If stainless fasteners or bolts are used underwater, lots of mastic must be placed on their threads, in the pre-drilled hole and under and around the head of the fastener to seal out moisture. These fasteners or bolts must be withdrawn periodically to inspect for crevice corrosion.
  
  Note: Stainless steel that is connected to a zinc anode or impressed-current protection system will not necessarily be protected. Crevice corrosion occurs where oxygen cannot get to the metal's surface. If oxygen can't get to the surface then it's very likely that protective current won't be able to either.
  
  Note: Use only 'austenitic' stainless steels in marine applications. These steels can be differentiated from other steels with a magnet, which will attract them very weakly or not at all. The stainless should preferably be type A4 (316) or better. Type A2 (304 or 18/8) stainless is the most common but is not as corrosion resistant as A4 (316)

• if propeller, prop shaft, or rudder shaft are stainless steel, waterproof grease or thread sealant is used to keep salt water out of threads, shaft taper and key way
  
  Note: Make sure grease is not graphite based.

• underwater stainless fittings are fastened with monel fasteners

• no gaskets containing asbestos or graphite and no underwater use of graphite based grease or graphite impregnated packing
  
  Asbestos and graphite are very noble in the galvanic series (opposite of zinc) and will, therefore, corrode most metals they are in contact with.

• no copper, mercury, or lead based anti-fouling paint on aluminium or mild steel
  
  In general, no metal based anti-fouling paint should be used on metal unless you know that they are compatible or an appropriate type of sealer coat is first applied to the bare metal.

• keel bolts in good condition and compatible with keel material

• centreboard pivot and lifting gear in good condition and made of compatible materials

• fittings that are in the bonding system are painted and isolated from wood as much as practicable
  
  Painting a fitting will reduce the amount of protective current it requires. Isolating it from the wood with paint or gaskets will protect the wood from hydroxides created by the protective current. These precautions minimise the damage by alkali rot to wood around protected fittings.

• if engine or its cooling system uses internal zinc anode protection, zinc anodes are not corroded away
  

Zinc anode corrosion protection system:

A protective current flows through metals that are electrically connected to the zinc anode. The current is forced by the galvanic voltage difference between the zinc anode and the underwater metal parts of the boat. Metals that are too far away from the zinc anode will receive little protective current.

• zinc anodes are bright, unpainted and not corroded away
  
  Note: There may be zinc anodes in the engine block, in heat exchangers, on the rudder, or on outdrives.

• zinc anode connection locked with star washer and moisture sealed
  
  Zinc anodes that are cast around a mounting bar are best. If you have stud mounted zinc anodes, use a waterproof mastic to seal in and around the mounting hole. This will help prevent corrosion that can lead to loosening of the zinc anode by undermining the stud connection.

• shaft zinc anodes not too near propeller
  
  A zinc anode on the shaft can cause turbulence which will decrease the efficiency of the propeller. Shaft zinc anodes also tend to protect only the forward part of the propeller. It's better to have hull-mounted-zinc anodes connected to the shaft via a shaft wiper (see Bonding System).

• appropriate protection current is flowing (10 to 25 mA, or more, per square foot of bare metal to be protected, depending on many factors)
  
  Note: Too much protective current can seriously damage wood or, in extreme cases, aluminium around protected fittings. Too little current will not provide adequate protection of fittings. With a wood hull, it's cheaper to err on the side of too little protective current since most underwater fittings are reasonably corrosion resistant anyway.

• there is a meter for monitoring protection current
  
  A protection current meter is easy to install with a hull-mounted-zinc anode system. It will show how much protection is being given and when zinc anodes need replacing. It will also indicate problems in the system, including stray currents. The meter should be 1 Amp (1000 mA) full scale and have a remote shunt. The shunt should have a pair of 40 Amp Schottky diodes wired in parallel with it, one in each direction, to protect the meter from lightning or electrical fault current surges. The remote shunt is important for allowing lightning strikes to flow directly to the sea, without first being routed up to your meter location.
  
  Note: Stray currents picked up by a bonding system will corrode any attached zinc anodes before damaging other metals.
  

Current limiting systems:

These systems are essentially the same as a hull-mounted-zinc anode system except that current limiting circuitry is placed in the wire running to the sacrificial zinc anode, allowing an extra large zinc anode to be used. Current is held at an appropriate level and the zinc anode may last for several years or more. These systems may have reference anodes mounted on the hull as well as the sacrificial zinc anodes.

• follow manufacturer's instructions for maintenance and make sure it's working...
  

Impressed-current systems:

Impressed-current systems 'force' a protective current to flow, using battery voltage instead of the natural voltage present between zinc anode and the bonding system. An underwater anode is still required but it is made of some non-corroding metal instead of zinc. Reference anodes may also be required with this system.

• follow manufacturer's instructions for maintenance and make sure it's working...

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Compass (traditional, fluxgate and autopilot compasses)

• not affected by operation of any of ship's equipment -- check on two perpendicular headings (e.g., N and W)
  
  Any DC current flow and most electronic devices can affect the compass if they're nearby. Check everything.
  

Note: AC current does not affect compasses so the next three points do not apply to 240 Volt wiring.

• no wires carrying heavy current nearby

• no single wires near compass
  
  The switch-panel's main earth wire and the alternator output wire are examples of potential problems because they carry a lot of current and they often run alone. When both positive and negative wires of a circuit run together, their opposite magnetic fields tend to cancel each other out.

• if wiring is nearby, it has both conductors tightly twisted together

• no speakers, swinging needle meters, transformers, ignition coils, or other magnetic devices nearby
  
  Speakers often contain powerful permanent magnets. They should be at least 1.5 m (5ft) away from any compass.

• no metal objects nearby unless they're non-magnetic
  
  Steel and iron usually cause most of the problems. Stainless steel and aluminium should be OK. All nearby metals should have their effect on the compass checked.

• autopilot and steering compasses separated by 1 m (3ft) or more (check their effect on each other)

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Electrical Interference (noise)

• GPS, autopilot, VHF, RADAR, depth sounder, etc. continue to operate properly when other electrical systems are turned on -- Do not perform this test with engine starting circuit or winch motor!
  
  No electronic device should be 'on' while the engine is being started or the winch is operating unless they are in an isolated circuit. The voltage transients or 'spikes' generated by starter and winch motors can cause damage to sensitive electronics. In this test, watch for noise generated by petrol engine ignition systems, alternator, DC to AC inverters, depth sounder, RADAR, strobe light, fluorescent lighting, electric motors, electric fuel pumps, VHF and SSB radios. Note that electronic noise can be transmitted through wires or air. For example, a GPS may have poor reception due to noise in its power cable or noise picked up by its aerial.

• autopilot, RADAR, inverter and SSB radio have their own circuits, with the wires running separately from wires for sensitive electronics

• able to isolate autopilot circuit
  
  Some electric autopilot motors can cause noise problems for electronics (e.g., GPS). If this happens, isolation is desirable. This can be achieved by directly wiring the autopilot circuit to one battery (at battery switch) and running the system on the other battery. Alternatively, the GPS can have an isolated power supply by having its own small battery, which is wired to the system with appropriate filters for charging.

• power wires for sensitive devices run separately from other wiring, especially alternator output, engine instrument and electric motor wires
  
  Wires that run parallel and close to each other can cause problems. However, wires may cross without affecting each other. Shielding may be required if close parallel wiring can't be avoided.
  
  If noise problems continue after following the above suggestions, filtering of offending and/or sensitive circuits may be necessary

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Miscellaneous

• depth sounder transducer is free of marine growth and has thin or no paint layer on bottom surface

• if LPG or petrol are used on board, appropriate sensing devices are installed to warn of leaks

• autopilot, VHF, RADAR, SSB and other critical, high-power devices have an input voltage that differs from battery voltage by less than 0.5 Volts while operating
  
  The voltage drop in a circuit is an indication of the condition of connectors, switches and wiring.

• solar panels have diodes in their circuits
  
  Without diodes, solar panels can take power from the batteries at night.

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Pre-Cruise Mini Check List

Maintenance check points are covered only briefly here. For explanations and construction check points, see the main sections of the check list

Batteries

• top surfaces clean and dry
• acid (electrolyte) level up to plastic liner inside holes
• fully charged specific gravity is 1.245 to 1.300 in each cell
• In a partially discharged battery, specific gravity of each cell does not vary by more than 0.050 from the other cells
• 'at rest' battery voltage is 12.1 to 12.8 Volts
• engine cranks properly for 5 seconds with each battery alone -- battery voltage is above 9.5 Volts and steady, while cranking
• cables are in good condition
• connections clean and sealed from moisture

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Wiring & Connections

• contact surfaces of mechanical connections are cleaned and coated with moisture resisting sealant before being put together
• no frayed or cracked insulation (check bilge and engine compartment)
• 12 Volt system leaks less than 5 mA of current (test)
• battery switch connections clean and sealed
• for each 'on' position, voltage drop is less than 0.5 Volts in battery switch, while engine is cranking
• fuses have clean, tight, sealed contacts
• every electrical system is documented in diagrams or schematics and these are in one location on board

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Alternator, Starter & Winch Motor

• with engine running, batteries fully charged, and a 1 or 2 Amp load on system (a light turned on), voltage to batteries is 13.9 to 14.4 Volts -- voltage remains constant as more loads are turned on, up to the rated output of the alternator
• brushes and slip rings or commutators are clean and in good condition
• bearings or bushings in good condition
• external connections clean, sealed from moisture, and positive terminals are covered
• alternator drive belt(s) tight and in good condition
• starter solenoid plunger clean and lubricated
• solenoid internal contacts clean and not pitted
• starter and winch motors get 9.0 Volts or more while operating

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Miscellaneous

• 240 Volt AC socket outlet faces clean and terminals coated with a moisture resistant sealant such as petroleum jelly (NOT Silicone)
• underwater stainless steel fittings and fasteners not pitted
• if engine or its cooling system uses internal zinc anode protection, zinc anodes are not corroded away
• corrosion protection zinc anodes bright, unpainted and not corroded away
• in corrosion protection system, appropriate protection current is flowing (10 to 25 mA, or more, per square foot of bare metal to be protected, depending on many factors)
• compasses not affected by operation of any of ship's equipment -- check on two perpendicular headings (e.g., N and W)
• GPS, autopilot, VHF, RADAR, etc. continue to operate properly when other electrical systems are turned on -- Do not perform this test with engine starting circuit or winch motor!
• depth sounder transducer is free of marine growth and has thin or no paint layer on bottom surface
• if LPG or petrol are used on board, appropriate sensing devices are installed to warn of leaks
• autopilot, VHF, RADAR, SSB and other critical, high-power devices have input voltage different from battery voltage by less than 0.5 Volts while operating

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Electrical System Spares

• fuses (check electronic devices for internal fuses)
• bulbs
• VHF aerial that will connect directly to radio
• alternator belt
• alternator brushes (most alternators have brushes)
• voltage regulator for alternator and/or a method of 'live wiring' alternator field coils for emergency charging
• 4 litres (1 gallon) of distilled water
• engine starter solenoid
• winch motor solenoid
• if petrol engine, complete set of ignition system parts
• plug-in AC socket outlet tester (has 3 indicator lights, costs £8 to £10)

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References

• The Bullet Proof Electrical System, Cruising Equipment Co., Seattle, 1986.
• Construction Standards for Small Vessels, Canadian Coast Guard, Ship Safety Branch, Part V, 1978.
• Corrosion Related Problems, Ed McClave, WoodenBoat magazine #93 (April, 1990), pp. 94-113.
• Electrolysis and Corrosion (3 parts), Jerry Kirschenbaum, WoodenBoat magazine #23, #24 & #25 (July - November, 1978).
• Metal Corrosion in Boats, Nigel Warren, 1980.
• Rules and Regulations for the Construction ... of Wood and Composite Boats, Lloyd's Register of Shipping, 1966, pp. 171-184.
• Standards and Recommended Practices for Small Craft, American Boat and Yacht Council, Inc., 1990-91.
• The 12 Volt Doctor's Practical Handbook, Edgar J. Beyn, 1983.
• Your Boat's Electrical System, Conrad Miller and E.S. Maloney, 1988.

Comments welcome!

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