Nautical terms
27 of 469 terms in Electrical & electronics. Show all
A
- AIS (Automatic Identification System, Class A AIS, Class B AIS) Electrical & electronics
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A radio system that automatically broadcasts a vessel's identity, type, position, course, speed and status to other ships and shore stations and shows theirs. Vessels required to carry it generally use Class A units; the simpler Class B is allowed for some of them and can be fitted voluntarily.
An AIS must be programmed with the boat's official MMSI and kept on and accurate once installed.
- Alternator (Voltage regulator, Regulator) Electrical & electronics
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The engine-driven generator that charges the batteries while the engine runs. It makes AC internally and converts it to DC; a voltage regulator keeps adjusting its output to the right charging voltage.
- Automatic charging relay (ACR) Electrical & electronics
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A relay that senses voltage and automatically connects two battery banks while a charging source is running, then separates them when charging stops, so both get charged but the house loads cannot flatten the starting battery.
Unlike a diode battery isolator, an ACR has no voltage drop to cause incomplete charging. Blue Sea's version connects the banks after seeing 13.0 volts for 2 minutes and separates them after 12.75 volts for 30 seconds.
- Autopilot (Heading sensor, Fluxgate compass, Rudder sensor) Electrical & electronics
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A system that steers the boat on a set heading or route: a heading sensor (often a fluxgate compass) tells a course computer where the bow points, and a drive moves the rudder to correct any error.
The NMEA warns autopilots can fail and invite complacency; their alarms help, but they do not replace a person keeping watch.
B
- Battery bank (House bank, House battery, Starting bank, Starting battery) Electrical & electronics
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A group of batteries wired together. The house bank runs the boat's DC loads; the starting bank is kept for starting the engine. Capacity is rated in amp-hours (what a battery delivers over 20 hours before falling to 10.5 volts); parallel wiring adds amp-hours, series wiring adds voltage.
- Battery charger (Three-stage charging, Multi-stage charger, Float charge) Electrical & electronics
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An AC-powered charger that recharges the batteries. Multi-stage chargers charge in steps, a fast bulk stage first and finally a lower float voltage that keeps a full battery topped up without overcharging.
- Battery switch (Battery selector switch, Paralleling switch, Emergency parallel) Electrical & electronics
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A heavy-duty switch that connects or disconnects the batteries from the boat's circuits. A paralleling switch can tie the house bank to the starting circuit to start the engine in an emergency.
- Bonding system (Bonding, Cathodic protection) Electrical & electronics
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Wiring that connects the underwater metal fittings and engine to each other and to the sacrificial anodes, so they are all protected together. ABYC technicians check this cathodic protection system.
C
- Chartplotter (Chart plotter) Electrical & electronics
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An electronic navigation display that shows the boat's GPS position on electronic charts, used to plan and follow routes. Many can also overlay radar on the chart.
- Circuit breaker (Breaker, Overcurrent protection) Electrical & electronics
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A switch-like device that opens a circuit automatically when current gets too high, protecting the wire from overheating. Unlike a fuse, which melts and must be replaced, a breaker can be reset.
ABYC standards call for the right fuses and breakers so wiring cannot overheat and start a fire.
D
- Deep-cycle battery (Deep cycle) Electrical & electronics
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A battery built with thick plates so it can be discharged deeply and recharged over and over, as house batteries are.
- Depth sounder (Echo sounder, Depth finder, Fishfinder, Transducer) Electrical & electronics
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An instrument that measures water depth by timing a sound pulse from a transducer on the hull to the bottom and back. Fishfinders use the same sonar to show fish and bottom structure.
A through-hull transducer is a hole in the boat; BoatUS Foundation warns removable ones must be locked in place or they can work loose and sink the boat.
- Digital selective calling (DSC, DSC distress button) Electrical & electronics
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A digital feature of modern VHF and HF radios that can "dial" and "ring" other radios directly and, with one button, send an automatic distress alert with the boat's identity and, if a GPS is connected, its position.
It works only with an MMSI programmed in; the Coast Guard recommends connecting the GPS to the radio. Hold the red distress button about 5 seconds, then continue on channel 16.
E
- ELCI (Equipment leakage circuit interrupter) Electrical & electronics
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A device on a boat's shore power system that interrupts the circuit when AC current leaks from it, guarding against stray AC in the water that can cause electric shock drowning. ABYC standards require one on new boats.
G
- Galvanic corrosion (Galvanic series, Dissimilar metals) Electrical & electronics
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Corrosion that happens when two different metals are electrically connected in water: the less noble metal (lower on the galvanic series) acts as the anode and wastes away, protecting the more noble one.
Boaters often call this "electrolysis", but that term strictly means chemical change caused by an electric current.
- Galvanic isolator Electrical & electronics
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A device wired into the green grounding wire of the shore power cord that blocks small DC galvanic currents from flowing through the shore ground wire, while still letting AC fault current pass. Most are a pair of diodes.
An isolation transformer does a similar job by coupling shore power to the boat magnetically, with no direct wire connection to the dock.
I
- Inverter Electrical & electronics
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A device that turns 12-volt (or 24- or 32-volt) DC from the batteries into 120-volt AC to run household-type appliances.
L
- Lead-acid battery (Flooded battery, Wet-cell battery, AGM battery, Gel battery, Gel cell) Electrical & electronics
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A battery of lead plates in sulfuric acid, made in three main types. Flooded (wet-cell) types need their water level checked and topped up and give off gas when charging; AGM and gel types are sealed, with the acid held in glass mat or gel, so they resist spills and leaks.
Charging lead-acid batteries gives off hydrogen, which is explosive; keep sparks and flame away.
M
- Marine wire (Tinned wire) Electrical & electronics
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Stranded, tin-plated copper wire suited to boats; never solid wire. Size it by American Wire Gauge (AWG) for the current and the round-trip length so voltage drop stays small, and finish ends with proper crimp terminals.
BoatUS Foundation recommends the most flexible (Type 3) wire, a voltage drop of no more than 3 percent, and wire strippers made for AWG rather than the smaller SAE gauge.
- MMSI (Maritime Mobile Service Identity) Electrical & electronics
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A nine-digit number that identifies a boat's DSC radio and AIS. U.S. numbers start with 338 or 366 to 369. Boats that need a station license get one from the FCC; recreational boats in U.S. waters can get one from BoatUS or America's Boating Club.
N
- NMEA 2000 (N2K, NMEA 0183) Electrical & electronics
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The standard network that lets marine electronics such as GPS, plotters, autopilots and instruments share data on a single network, with many devices both talking and listening. Its older predecessor, NMEA 0183, is a simple serial link where one device talks to several listeners.
R
- Radar Electrical & electronics
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An electronic system that uses radio waves to detect other boats, land and buoys and show their positions, useful at night and in poor visibility. The Navigation Rules require proper use of radar if it is fitted.
Recreational radar needs no FCC license. Overlaying radar on the chart requires a heading sensor.
discoverboating.com · navcen.uscg.gov · uscgboating.org · nmea.org
- Reverse polarity Electrical & electronics
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A wiring fault in which the hot and neutral wires of an AC circuit are swapped, which can be very dangerous. Most boat AC panels have an indicator light that warns of it.
S
- Sacrificial anode (Zinc, Zincs, Anode, Zinc anode, Pencil zinc) Electrical & electronics
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A piece of less noble metal, most often zinc, fastened to underwater metal or inside an engine's cooling system so it corrodes instead of the propeller, shaft, outdrive or heat exchanger.
BoatUS Foundation says replace zincs that are badly eroded, and zincs gone after one season point to a bonding or electrical problem. Westerbeke checks the engine zinc monthly.
bluesea.com · discoverboating.com · boatus.org · westerbeke.com · boatus.com
- Shore power (Shore power cord, Shore cord) Electrical & electronics
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AC electricity from the dock's utility supply, brought aboard through a shore power cord to run the boat's AC outlets and equipment while it is tied up.
ABYC-certified technicians check shore power connections, and ABYC standards now call for an ELCI on the shore power system of new boats.
- Stray current corrosion (Stray current) Electrical & electronics
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Corrosion caused when current from a battery or other outside DC source, such as a partial short in the wiring, makes an underwater metal part act as an anode so it wastes away.
V
- VHF radio (VHF, VHF-FM, Marine radio) Electrical & electronics
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The main short-range marine radio, working on the very high frequency band. Channel 16 is for distress and calling; channel 9 is the recreational calling channel. Recreational boats on domestic trips generally need no FCC license to use one.
Most recreational boats under 65.6 feet (20 m) are not required to carry a radio, but any radio aboard must be used under FCC rules.
uscgboating.org · dco.uscg.mil · discoverboating.com · fcc.gov
General guidance for recreational boaters, researched from the sources listed and written in our own words. Your equipment manuals, local knowledge, the Navigation Rules and a qualified instructor come first.