A/D Converter - A device that changes an analog signal (such as voltage) into a digital signal (discrete data values.)

Accelerometer - A sensor that measures acceleration. Acceleration can be due to gravity or changing motion. Acceleration is measured in units of earth's gravity (G's) or meters per second squared.

Bandwidth - The frequency range within which the product will be able to accurately measure signals. Specified in Hz.

Bias Stability - The maximum expected drift in a sensor’s output. This can be measured as a function of time or as a function of temperature.

Bight - The part of the rope or line, between the end and the standing part, on which a knot is formed.
Bilge - The interior of the hull below the floor boards.
Bitter End - The last part of a rope or chain. The inboard end of the anchor rode.
Blink - I Loran-C, a signal used to indicate that a station is malfunctioning. Intended to prevent the use of that signal for navigation.
Boat - A fairly indefinite term. A waterborne vehicle smaller than a ship. One definition is a small craft carried aboard a ship.
Boat Hook - A short shaft with a fitting at one end shaped to facilitate use in putting a line over a piling, recovering an object dropped overboard, or in pushing or fending off.
Boot Top - A painted line that indicates the designed waterline.
Bow - The forward part of a boat.
Bow Line - A docking line leading from the bow.
Bowline - A knot used to form a temporary loop in the end of a line.
Bridge - The location from which a vessel is steered and its speed controlled. "Control Station" is really a more appropriate term for small craft.
Bridle - A line or wire secured at both ends in order to distribute a strain between two points.
Brightwork - Varnished woodwork and/or polished metal.
Bulkhead - A vertical partition separating compartments.
Buoy - An anchored float used for marking a position on the water or a hazard or a shoal and for mooring.
Burdened Vessel - That vessel which, according to the applicable Navigation Rules, must give way to the privileged vessel. The term has been superseded by the term "give-way".
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C


Cabin - A compartment for passengers or crew.
Calibration - A general term for any kind of alignment procedure or compensation routines to improve the accuracy of a sensor.

Capsize - To turn over.
Cast Off - To let go.
Catamaran - A twin-hulled boat, with hulls side by side.
Chafing Gear - Tubing or cloth wrapping used to protect a line from chafing on a rough surface.
Chart - A map for use by navigators.
Checksum - For the NMEA 0183 standard, a validity check performed on the data contained in the sentences, calculated by the talker, appended to the message, then recalculated by the listener comparison to determine if the message was received correctly.
Chine - The intersection of the bottom and sides of a flat or v-bottomed boat.
Chock - A fitting through which anchor or mooring lines are led. Usually U-shaped to reduce chafe.
Cleat - A fitting to which lines are made fast. The classic cleat to which lines are belayed is approximately anvil-shaped.
Clove Hitch - A knot for temporarily fastening a line to a spar or piling.
Coaming - A vertical piece around the edge of a cockpit, hatch, etc. to prevent water on deck from running below.
Cockpit - An opening in the deck from which the boat is handled.
Coil - To lay a line down in circular turns.
Communication Protocol - A method established for message transfer between a talker and a listener, which includes the message format and the sequence in which the messages are to be transferred. Also includes the signaling requirements such as baud rate, stop bits, parity, and bits per character.
Course - The horizontal direction in a which a vessel is steered or intended to be steered, expressed as angular distance from north, usually from 000� at north, clockwise through 359�. Strictly, the term applies to direction through the water, not the direction intended to be made good over the ground (see Track). Differs from heading.
Course over ground (COG) - Term used to refer to the direction of the path over ground actually followed by a vessel [a misnomer in that courses are directions steered or intended through the water with respect to a reference meridian]
CRC - Cyclical Redundancy Check. Used within the NMEA 2000^® standard as a type of check value designed to catch transmission errors. The transmitter calculates and sends the CRC appended to the end of the data where the receiver calculates a CRC based on the received data and compares it to the received CRC. A mismatch indicates that the data was corrupted in transit.

Cross track error (XTE) - the distance from the vessel's present position to the closest point on a line between the origin and destination waypoints of the navigation leg being traveled.
Cuddy - A small shelter cabin in a boat.
Current - The horizontal movement of water.
Cycle lock - In Loran C, the comparison, in time difference, between corresponding carrier cycles contained in the rise times of a master and slave station pulse is called cycle match. This value when refined to a determination of the phase difference between these two cycles results in cycle lock. (See also Envelope-to-Cycle Distortion).
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D

D/A Converter - (Digital to Analog Converter, also abbreviated DAC) Converts a digital signal (discrete values) to an analog voltage.

Data field - In an NMEA 0183 sentence, a field that contains a data value.
Dead Ahead - Directly ahead.
Dead Astern - Directly aft.
Dead Reckoning - The process of determining the position of a vessel at any instant by applying to the last well-determined position (point of departure or subsequent fix) the run that has since been made, usually based on the recent history of speed and heading measurements.
Decca Chain - A group of associated stations of the Decca Navigator System. A Decca chain normally consists of a master and three secondary stations. Each station is balled by the color of associated stations. Each station is called by the color of associated pattern of hyperbolic lines as printed on the chart, i.e., red, green, and purple.
Decca Navigator System - A short to medium range low frequency (70-130 kHz) radio-navigation system by which a hyperbolic line of position of high accuracy is obtained. The system is an arrangement of fixed, phase locked, continuous wave transmitters operating on harmonically related frequencies and special receiving equipment located on a vessel. The operation of the system depends of phase comparison of the signals from the transmitters brought to a common comparison frequency with the receiver.
Deck - A permanent covering over a compartment, hull or any part thereof.
Delimiter(s) - In the NMEA 0183 standard, a character or characters used to separate fields or sentences. The following delimiters are used in the NMEA 0183 standard:

Field delimiters:

• ASCII �$� (HEX 24) for address field
• ASCII �,� (HEX 2C) for data fields
• ASCII �*� (HEX2A) for checksum field sentence delimiters
• carriage return and line feed (HEX 0D0A) [note: is not required preceding the first sentence transmitted]

Depth Sounder - An instrument that determines the depth of water by measuring the time interval between the emissions of a sound and the return of its echo from the bottom.
Destination - The immediate geographic point of interest to which a vessel is navigating. It may be the next waypoint along a route of waypoints or a final destination of a voyage.
Deviation - The deflection of a compass needle caused by local magnetic influence.
Deviated - Term used to indicate that a compass has been corrected for Deviation
DGNSS - Differential GNSS, the use of GNSS measurements, some or all of which are differentially corrected.
DGPS - Differential GPS, the use of GPS measurements, which are differentially corrected.
Dinghy - A small open boat. A dinghy is often used as a tender for a larger craft.
Displacement - The weight of water displaced by a floating vessel, thus, a boat's weight.
Displacement Hull - A type of hull that plows through the water, displacing a weight of water equal to its own weight, even when more power is added.
Dock - A protected water area in which vessels are moored. The term is often used to denote a pier or a wharf.
Dolphin - A group of piles driven close together and bound with wire cables into a single structure.
Doppler Speed Log - An instrument which measures the relative motion between a vessel and the reflective sea bottom (for bottom return mode) or suspended particulate matter in the seawater itself (for water return mode) by measuring the frequency shifts between a transmitted and subsequently echoed acoustic or electromagnetic signal.
Draft - The depth of water a boat draws.
Drift - The speed of a current.

DSP - Digital Signal Processor. This is a microprocessor optimized for digital signal manipulations.

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E


Ebb - A receding current.
Echo Sounder - (see Depth Sounder).
EGNOS (European Geostationary Navigation Overlay Service) - The European Satellite Based Augmentation System (see SBAS).

Envelope-to-Cycle Distortion (ECD) - The time relationship between the phase of the Loran-C carrier and the time origin of the envelope waveform.
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F

Fathom - Six feet.
Fender - A cushion, placed between boats, or between a boat and a pier, to prevent damage.

Fiber Optic Gyro - A high accuracy rate sensor that uses a laser and fiber optic ring to determine angular rate.
Figure Eight Knot - A knot in the form of a figure eight, placed in the end of a line to prevent the line from passing through a grommet or a block.
Field - In the NMEA 0183 standard, a character or string of characters immediately preceded by a field delimiter (see Delimiters). In NMEA 2000^®, fields of data that make up a PGN.
Fixed Field - In the NMEA 0183 standard, a field in which the number of characters is fixed. For data fields, such fields are shown in the sentence definitions with no decimal point. Other fields that fall into this category are the address field and the checksum field.
Flare - The outward curve of a vessel's sides near the bow. A distress signal.
Flood - An incoming current.
Floorboards - The surface of the cockpit on which the crew stand.
Fluke - The palm of an anchor.
Following Sea - An overtaking sea that comes from astern.
Fore-and-Aft - In a line parallel to the keel.
Forepeak - A compartment in the bow of a small boat.
Forward - Toward the bow of the boat.
Fouled - Any piece of equipment that is jammed or entangled, or dirtied.
Freeboard - The minimum vertical distance from the surface of the water to the gunwale.

Frequency Range - See "bandwidth".
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G

Galley - The kitchen area of a boat.
Gangway - The area of a ship's side where people board and disembark.
Gear - A general term for ropes, blocks, tackle and other equipment.
Geoid - A surface along which the gravity potential is everywhere equal (equipotential surface) and to which the direction of gravity is always perpendicular.
Geometric Dilution of Precision (GDOP) - A value representing all geometric factors that degrade the accuracy of a position fix which has been derived from a navigation system.
Give-Way Vessel - A term used to describe the vessel that must yield in meeting, crossing, or overtaking situations.
Global Navigation Satellite System (GNSS) - Any single or combined satellite navigation system. Currently the options are: GPS, GLONASS, and combined GPS/GLONASS.
Global positioning system (GPS) - GPS is defined as the constellation of satellites, the navigation payloads which produce the GPS signals, ground stations, data links, and associated command and control facilities which are operated and maintained by the Department of Defense; the Standard Positioning Service (SPS) as the civil and commercial service provided by the basic GPS; and augmentations as those systems based on the GPS that provide real-time accuracy greater than the SPS. GPS permits land, sea, and airborne users to determine their three dimensional position, velocity, and time, 24 hours a day in all weather, anywhere in the world.
GLONASS - An all weather, continuous satellite navigation system, maintained by the Russian Space Forces. Normally composed of 24 satellites in 3 orbital planes with 8 satellites in each plane. The spacing of satellites in orbit is arranged so that a minimum of four satellites will be in view to users worldwide to provide position dilution of precision (PDOP) of 6 or less.
Grab Rails - Hand-hold fittings mounted on cabin tops and sides for personal safety when moving around the boat.
Great Circle - The intersection of the surface of a sphere and a plane through its center.
Great Circle Chart - A chart on which a great circle appears approximately as a straight line.
Great Circle Direction - Horizontal direction of a great circle, expressed as angular distance from a reference direction.
Ground Tackle - A collective term for the anchor and its associated gear.
Group Repetition Interval (GRI) - Of a particular Loran-C chain, the specified time interval for all stations of the chain to transmit their pulse groups. For each chain a minimum group repetition interval is selected of sufficient duration to provide time for each station to transmit its pulse group and additional time between each pulse group so that signals from the two or more stations cannot overlap in time anywhere within the coverage area.
Gunwale - The upper edge of a boat's sides.
Gyrocompass - A compass having one or more gyroscopes as the directive element, and which is north-seeking. Its operation depends upon four natural phenomena: gyroscopic inertia, gyroscopic precession, the earth's rotation, and gravity.
Gyropilot - An automatic device for steering a vessel by means of control signals received from a gyrocompass (see Autopilot).
Gyroscope - A rapidly rotating mass free to move about one or both axes perpendicular to the axis of rotation and to each other.
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H

Hard Chine - An abrupt intersection between the hull side and the hull bottom of a boat so constructed.
Hatch - An opening in a boat's deck fitted with a watertight cover.
Head - A marine toilet. Also the upper corner of a triangular sail.
Heading - The horizontal direction in which a ship actually points or heads at any instant, expressed in angular units from a reference direction, usually from 000� at the reference direction clockwise through 359�. (see True Heading and Magnetic Heading).
Heading-to-Steer - The difference between the bearing to destination (from present position) and track-made-good, applied to the bearing to the destination.
Headway - The forward motion of a boat. Opposite of sternway.
Helm - The wheel or tiller controlling the rudder.
Helmsperson - The person who steers the boat.
Hitch - A knot used to secure a rope to another object or to another rope, or to form a loop or a noose in a rope.
Hold - A compartment below deck in a large vessel, used solely for carrying cargo.
Horizontal Dilution of Precision (HDOP) - similar to GDOP, except elevation factors are ignored.
Hull - The main body of a vessel.
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I

Inboard - More toward the center of a vessel; inside; a motor fitted inside a boat.
Intracoastal Waterway (ICW) - Bays, rivers, and canals along the coasts (such as the Atlantic and Gulf of Mexico coasts), connected so that vessels may travel without going into the sea.
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J

Jacobs Ladder - A rope ladder, lowered from the deck, as when pilots or passengers come aboard.
Jetty - A structure, usually masonry, projecting out from the shore; a jetty may protect a harbor entrance.
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K

Keel - A longitudinal timber or plate extending along the center of the bottom of a ship and often projecting from the bottom.
Knot (1) - A measure of speed equal to one nautical mile (6076 feet) per hour.
Knot (2) - A fastening made by interweaving rope to form a stopper, to enclose or bind an object, to form a loop or a noose, to tie a small rope to an object, or to tie the ends of two small ropes together.
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L

Latitude - The distance north or south of the equator measured and expressed in degrees.
Lazarette - A storage space in a boat's stern area.
Lee - The side sheltered from the wind.
Leeward - The direction away from the wind. Opposite of windward.
Leeway - The sideways movement of the boat caused by either wind or current.
Line - Rope and cordage used aboard a vessel.
Line of Position (LOP) - In Loran or Decca navigation systems, a vector obtained by measurement of the time difference between the receipt of the master and slave signals which is then used to selected a corresponding LOP from a chart or table. Two or more intersecting LOPs are required to obtain a position fix.
Listener - In the NMEA 0183 standard, the recipient of messages across an interconnecting link.
Longitude - The distance in degrees east or west of the meridian at Greenwich, England.
Log - An instrument for measuring the speed or distance or both traveled by a vessel.
Loran - The general designation of one group of radionavigation systems by which a hyperbolic line of position is determined through measuring the difference in the times of reception of synchronized pulse signals from two fixed transmitters.
Lubber's Line - A mark or permanent line on a compass indicating the direction forward parallel to the keel when properly installed.
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M

Magnetic Bearing - Bearing relative to magnetic north; compass bearing corrected for deviation.
Manufacturer Identification Code - In the NMEA 0183 standard, a three character manufacturer identifier, usually an acronym derived from the company name, which has been approved and is listed in Appendix III, for use by a manufacturer as part of the address field in formulation of proprietary sentences.
Marlinspike - A tool for opening the strands of a rope while splicing.
MEMS - Micro-Electro-Mechanical Structures. These devices rely on both their electrical and physical properties to operate.

Message - In the NMEA 0183 standard, a message consists of 2 or more sentences with the same sentence formatter. Messages are used when 2 or more sentences are needed to convey related data that exceeds the maximum sentence length. This only applies to those sentence formatters that are defined with the key fields supporting multi-sentence messages.
Mercator Map Projection - A conformal cylindrical map projection in which the surface of a sphere or spheroid, such as earth, is conceived as developed on a cylinder tangent along the equator. Meridians appear as equally spaced vertical lines and parallels as horizontal lines drawn farther apart as the latitude increases, such that the correct relationship between latitude and longitude scales at any point is maintained.
Midship - Approximately in the location equally distant from the bow and stern.
Mooring - An arrangement for securing a boat to a mooring buoy or a pier.

MSAS (MTSAT Satellite-based Augmentation System) - Far East Satellite Based Augmentation System (see SBAS).

MTBF - Mean Time Between Failures. This is an indication of the reliability of a product in normal use
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N

Nautical Mile - One minute of latitude; approximately 6076 feet - about 1/8 longer than the statute mile of 5280 feet.
Navigation - The art and science of conducting a boat safely from one point to another.
Navigation Leg - The portion of as voyage upon which the vessel currently travels. Each leg consists of two waypoints, an Origin, a Destination, and a line between them upon which the vessel travels.
Navigation Rules - The regulations governing the movement of vessels in relation to each other, generally called steering and sailing rules.
Navy Navigation Satellite System (TRANSIT) - An obsolete satellite navigation system of the United States conceived and developed by the Applied Physics Laboratory of John Hopkins University for the U.S. Navy. It is an all-weather, worldwide, and passive system used primarily for the navigation of surface ships and submarines. Also known by the acronyms NAVSAT or TRANSIT, it consists of a constellation of orbiting satellites, a ground system of tracking station, and any number of user stations (navigators). The user stations are radionavigation devices composed of a receiver, a frequency cycle-counter, and a computer. The minimum constellation for system operation is four satellites (five satellites in orbit provided redundancy). The satellite orbits are controlled by the tracking stations. Satellites broadcast current known positions while orbiting the earth. The NAVSAT system utilizes the Doppler shift of radio signals transmitted from the satellite to measure the relative velocity between the satellite and the navigator. Knowing the satellite orbit precisely, the navigator's absolute position can be accurately determined from this time rate of change of range to the satellite.
NMEA - National Marine Electronics Association.
NMEA 0183 - A One-Way Communication Protocol standard developed in the 1970’s by the National Marine Electronics Association (NMEA) for interfacing marine electronic devices.
NMEA 2000^® - A Two-Way Communication Protocol standard established in the late 1990’s and early 2000^®’s by the National Marine Electronics Association (NMEA) for interfacing marine electronic devices.
Noise - Additional signals, coming from electronic equipment, that interfere with signals you are trying to measure.
Noise Density - A measure of noise as a function of frequency (e.g. mG/ Hz1/2) Generally, the larger the bandwidth of your measurement, the more noise you include in your measurement.
Null Field - In the NMEA 0183 standard, indicates that data is not available for the field. Indicated by two ASCII commas, i.e., �,,� (HEX 2C2C), or, for the last data field in a sentence, one comma followed by the checksum delimiter �,*� (HEX 2C2A) [Note: the ASCII Null character (HEX2C2A). [Note: the ASCII Null character (HEX 00) is not to be used for null fields!]
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O

Omega Navigation System - An obsolete worldwide, continuous, radionavigation system of medium accuracy that provideed hyperbolic lines of position through phase comparisons of VLF (10-14 kHz) continuous wave signals transmitted on a common frequency on a time-shared basis. The fully implemented system was comprised of eight transmitting stations.
One-Way Communication Protocol - A protocol established between a talker and a listener in which only the talker may send messages [compare to Two-Way Communication Protocol]. NMEA 0183 is a One-Way Communication Protocol.
Origin Waypoint - The starting point of the present navigation leg.
Outboard - Toward or beyond the boat's sides. A detachable engine mounted on a boat's stern.
Overboard - Over the side or out of the boat.
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P

PGN - Parameter Group Number (PGN). The NMEA 2000^® standard refers to a packet of information as a PGN, this is opposed to the NMEA 0183 standard that refers to a packet of information as a sentence.
Pier - A loading platform extending at an angle from the shore.
Pile - A wood, metal or concrete pole driven into the bottom. Craft may be made fast to a pile; it may be used to support a pier (see Piling) or a float.
Piling - Support, protection for wharves, piers etc.; constructed of piles (see Pile)
Piloting - Navigation by use of visible references, the depth of the water, etcetera.
Pitch - Rotation around the Y-Axis. In a plane, this is the rotation around the axis defined by the wings.

Planing - A boat is said to be planing when it is essentially moving over the top of the water rather than through the water.
Planing Hull - A type of hull shaped to glide easily across the water at high speed.
Port - The left side of a boat looking forward. A harbor.
Precision - A measure of how close the outcome of a series of observations or measurements cluster about some estimated value of a desired quantity, such as the average value of a series of observations of a quantity. Precision implies repeatability of the observations within some specified limit and depends upon the random errors encountered due to the quality of the observing equipment, the skill of the observer and randomly fluctuating conditions such as temperature, pressure, refraction, etc. [compare with Accuracy].
Privileged Vessel - A vessel that, according to the applicable Navigation Rule, has right-of-way (this term has been superseded by the term "stand-on").
Proprietary Sentence - A sentence to be sent across the interconnecting link which is not included in the List of Approved Sentences of the NMEA 0183 standard. All proprietary sentences sent over the interconnecting link shall contain a unique talker identifier that begins with a �P� (HEX 50) followed by a three-character manufacturer identification code.
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Q

Quarter - The sides of a boat aft of amidships.
Quartering Sea - Sea coming on a boat's quarter.
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R

Rate Gyro - A special kind of gyroscope that measures rotation rate around a fixed axis.

Relative Bearing - Bearing relative to heading or to the vessel.
Relative Wind - The speed and relative direction to from which the wind appears to blow with reference to a moving point (also called Apparent Wind)
Repeatability - The maximum variation between repeated measurements under the same conditions.

Resolution - The smallest change that a sensor can measure.
Rhumb Line - A line on the surface of the earth making the same oblique angle with all meridians. A rhumb line is a straight line on a rhumb (or Mercator) direction.
Rhumb Direction - The horizontal direction of a rhumb line, expressed as angular distance from a reference direction. Also known as Mercator direction (see Mercator Map Projection).
RMA sentence - Recommended Minimum Acceptable Sentence, a composite sentence recommended by the NMEA 0183 standard to insure interoperability between talkers and listeners and to insure that all data considered necessary for navigation is sent by a particular navigation unit.
Rode - The anchor line and/or chain.
Roll - Rotation around the X-Axis. In a vessel, roll is rotation about the axis defined by the vessels fore-and-aft center line.
Rope - In general, cordage as it is purchased at the store. When it comes aboard a vessel and is put to use it becomes line.
Route - A planned course of travel, usually composed of more than one navigation leg.
Route System - Any system of one or more routes and/or routing measures aimed at reducing the risk of casualties during a voyage which may include such items as traffic separation schemes, recommended tracks, restricted areas, inshore traffic zones, etc.
RS-232 Interface - Standard serial interface for PC-type computers.

Rudder - A vertical plate or board for steering a boat.
Run - To allow a line to feed freely.
Running Lights - Lights required to be shown on boats underway between sundown and sunup.
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S

Sampling Rate - The number of readings an A/D converter takes per amount of time. For example, 50 readings per second.

Satellite Based Augmentation System (SBAS) - An augmentation to GNSS that uses geostationary satellites to broadcast GNSS integrity and correction data, and additional ranging signals.
Satellite Navigation - A form of position finding using radio transmissions from satellites with sophisticated on-board automatic equipment.
Scope - Technically, the ratio of length of anchor rode in use to the vertical distance from the bow of the vessel to the bottom of the water. Usually six to seven to one for calm weather and more scope in storm conditions.
Screw - A boat's propeller.
Scuppers - Drain holes on deck, in the toe rail, or in bulwarks or (with drain pipes) in the deck itself.
Sea Cock - A through hull valve, a shut off on a plumbing or drain pipe between the vessel's interior and the sea.
Seamanship - All the arts and skills of boat handling, ranging from maintenence and repairs to piloting, sail handling, marlinespike work, and rigging.
Sea Room - A safe distance from the shore or other hazards.
Seaworthy - A boat or a boat's gear able to meet the usual sea conditions.
Secure - To make fast.
Selected Waypoint - The waypoint currently selected to be the point toward which the vessel is traveling. Also called “TO” Waypoint, destination or destination waypoint.
Semi-Fixed Field - NMEA 0183 data fields having a base other than 10, but use base 10 to express precision of the final term (such as minutes expressed as units with a decimal trailer instead of seconds in a base 60 field, or seconds expressed with a decimal trailer).
Sensitivity - The ratio of output volts to sensor output range (e.g., V/G.) Sensitivity allows you to predict the sensor response to a sensor input.

Sentence Formatter - In the NMEA 0183 standard, a three character sentence identifier which follows the talker identifier which follows the talker identifier which follows the talker identifier and is included as part of the address field. The sentence formatters are an integral part of the sentence definitions provided by this standard and attached appendices.
Set - The directions towards which a current flows.
Ship - A larger vessel usually thought of as being used for ocean travel. A vessel able to carry a "boat" on board.
Signal-to-Noise Ratio (SNR) - The ratio of the magnitude of a signal to that of the noise (interference), often expressed in decibels.
Slack - Not fastened; loose. Also, to loosen.
Sole - Cabin or saloon floor. Timber extensions on the bottom of the rudder. Also the molded fiberglass deck of a cockpit.
Solid-State Technology - A general term for sensors that do not have moving parts.

Sounding - A measurement of the depth of water.
Speed Log - An instrument for measuring vessel speed through water and/or speed over ground. A single axis speed log normally measures speed along the longitudinal (fore/aft) axis of the vessel, while a dual axis speed log measures speed along the transverse (port-starboard) axis as well. (Also see Doppler Speed Log).
Speed Made Good - The adjusted speed, which takes into account factors such as drift and wind speed. Can be estimated or computed by a navigation receiver.
Spring Line - A pivot line used in docking, undocking, or to prevent the boat from moving forward or astern while made fast to a dock.
Squall - A sudden, violent wind often accompanied by rain.
Square Knot - A knot used to join two lines of similar size. Also called a reef knot.
Standing Part - That part of a line which is made fast.The main part of a line as distinguished from the bight and the end.
Stand-On Vessel - That vessel which has right-of-way during a meeting, crossing, or overtaking situation.
Starboard - The right side of a boat when looking forward.
Stem - The forward most part of the bow.
Stern - The after part of the boat.
Stern Line - A docking line leading from the stern.
Stow - To put an item in its proper place.
Supply Current - the typical current that must be supplied to a product along with the supply voltage.
Supply Voltage - the amount of voltage the user must supply to a product for the product to work properly.
Swamp - To fill with water, but not settle to the bottom.
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T

Talker - In the NMEA 0183 Standard, the originator of messages across an NMEA 0183 link.
Talker Identifier - The first two characters following the �$� (HEX 24) in an NMEA 0183 sentence (address characters 1 and 2.
Temperature Range - the temperatures between which the product will accurately operate.

Time Difference (TD) - In Loran-C, the time difference measured from the time of reception of the mater station signal to the time of reception of the slave station signal.
Track - The intended or desired horizontal direction of travel with respect to the earth. The track expressed in degrees of the compass may differ from the course due to allowances made in the course due to allowances made in the course for such factors as sea and weather conditions in order to resume the desired track.
Track Made Good - A single resultant direction from a point of departure to a point of arrival at any given time.
Transducer - A device that converts one type of energy to another, as a loudspeaker that changes electrical energy into acoustical energy.
True Bearing - Bearing relative to true north; compass bearing corrected for compass error.
True Heading - Heading relative to true north.
Two-Way Communication Protocol - A protocol established between a talker and a listener in which the listener may also issue requests to the talker when required [compare to One-Way Communication Protocol]. NMEA 2000^® is a Two-Way Communication Protocol.
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U

UAIS - See AIS.
UART - Universal Asynchronous Receiver Transmitter that produces an electrical signal and timing for transmission of data over a communications path, and circuitry for detection and capture of such data transmitted from another UART.
Unicode - The Unicode standard is a fixed-width, uniform encoding scheme from written characters and text. The Unicode character encoding treats alphabetic characters, ideographic characters, and symbols identically, which means they can be used in any mixture and with equal facility. The Unicode Standard is molded on the ASCII character set, but uses 16 bit encoding to support full multilingual text. No escape sequence or control code is required to specify any character in any language. See the TUT sentence for application of Unicode within the NMEA 0183 standard.
Universal Time Coordinated (UTC) - A time scale based on the rotation of the earth that is disseminated by most broadcast time services [compare with atomic time].
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V

Variable Field - In NMEA 0183 sentences, a data field which may or may not contain a decimal point and which may vary in precision following the decimal point depending on the requirements and the accuracy of the measuring device (talker).
Variation - The angle between the magnetic and geographic meridians at any place, expressed in degrees and minutes east or west to indicate the direction of magnetic north from true north.
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W

Waypoint - A reference point on a track
Wide Area Augmentation System (WAAS) - The Americas Satellite Based Augmentation System (see SBAS).