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

abaft
Toward the rear (stern) of the boat.

abeam
At right angles to the keel of the boat, but not on the boat.

aboard
On or within the boat.

above deck
On the deck (not over it - see Aloft)

abreast
Side by side; by the side of.

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.

accuracy
In navigation, a measure of the error between the point desired and the point achieved, or between the position indicated by measurement and the true position [compare with precision]

additional secondary factor
In Loran-C, a correction in addition to the secondary phase factor correction for the additional time (or phase delay) for transmission of a low frequency signal over a composite land-seawater path when the signal transit is based on the free-space velocity.

address field
For sentences in the NMEA 0183 standard, the fixed length field following the beginning sentence delimiter "$" (HEX 24). For approved sentences, composed of a two-character talker identifier and a three-way character sentence formatter. For proprietary sentences, composed of the character "P" (HEX 50) followed by a three-character manufacturer identification code.

adrift
Loose, not on moorings or towline.

aft
Toward the stern of the boat.

aground
Touching or fast to the bottom.

ahead
In a forward direction.

aids To navigation
Artificial objects to supplement natural landmarks indicating safe and unsafe waters.

AIS
Universal Shipborne Automatic Identification System (AIS). AIS operate primarily on VHF radio frequencies, with a coverage range of 20 to 30 nautical miles. AIS provides a means to automatically exchange information between ships and with hore stations, information that can be used for identification purposes or for monitoring and tracking the movements of ships. Ship information updates range from between every 2 seconds to 6 minutes, depending upon the speed of the ship. Information broadcast by each AIS equipped ship and an information from land such as from Vessel Traffic Services (VTS) is automatically received by each AIS equipped ship within VHF radio range.

alee
Away from the direction of the wind. Opposite of windward.

aloft
Above the deck of the boat.

amidships
In or toward the center of the boat.

anchorage
A place suitable for anchoring in relation to the wind, seas and bottom.

apparent wind
The speed and relative direction to from which the wind appears to blow with reference to a moving point (also called Relative Wind).

approved sentence
An NMEA 0183 sentence that has been approved for general use by the NMEA general assembly and is listed in this standard and attached Appendices.

arrival alarm
An alarm signal issued to indicates arrival at or at a pre-determined distance from a waypoint (see Arrival Circle).

arrival circle
An artificial boundary placed around the destination waypoint of the present navigation leg, the entering of which will signal an arrival alarm.

arrival perpendicular
Crossing of the line which is perpendicular to the course line and which passes through the destination waypoint.

ASCII
American Standard Code for Information Interchange. A 7 bit wide serial code describing numbers, upper and lower case alpha, characters, special and non-printing characters. See American National Standards Institute documents ANSI X 3.15, ANSI X 3.16 and ANSI 3.4.

astern
In back of the boat, opposite of ahead.

athwartships
At right angles to the centerline of the boat; rowboat seats are generally athwart ships.

atomic time
Time obtained by counting cycles of a signal in resonance with certain kinds of atoms.

autopilot
An automatic device for steering a vessel so as to maintain its heading in an intended direction. Mechanical means are used to steer the rudder. A navigation system is often connected to correct for track errors, or to select new destinations.

aweigh
The position of anchor as it is raised clear of the bottom.

azimuth
The horizontal direction of a celestial point from a terrestrial point, expressed as the angular distance from a reference direction, usually measured from 000° at the reference direction through 359°.

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

batten down
Secure hatches and loose objects both within the hull and on deck.

beam
The greatest width of the boat.

bearing
The horizontal direction of one terrestrial point from another, expressed as the angular distance from a reference direction, usually measured from 000&qdeg; at the reference direction clockwise through 359°

Beaufort wind scale
A numerical scale for indicating wind speed. Beaufort numbers (or forces) range from force 0 (calm) to force 12 (hurricane).

below
Beneath the deck.

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".

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.

COG
Course over Ground. 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].

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
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
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).

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
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.

deviated
Term used to indicate that a compass has been corrected for Deviation

deviation
The deflection of a compass needle caused by local magnetic influence.

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.

ebb
A receding current.

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

echo 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.

EGNOS
European Geostationary Navigation Overlay Service. The European Satellite Based Augmentation System (see SBAS).

envelope-to-cycle distortion
The time relationship between the phase of the Loran-C carrier and the time origin of the envelope waveform.

European Geostationary Navigation Overlay Service
The European Satellite Based Augmentation System (see SBAS).

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.

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.

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.

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".

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 GDOP

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 is defined as the constellation of satellites, the navigation payloads which produce the GPS signals, ground Global positioning system (GPS)

GNSS
Global Navigation Satellite System. Any single or combined satellite navigation system. Currently the options are: GPS, GLONASS, and combined GPS/GLONASS.

GPS
Global Positioning System is defined as the constellation of satellites, the navigation payloads which produce the GPS signals, ground GLONASS

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.

GRI
Group Repetition Interval. 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.

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.

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.

HDOP
Horizontal Dilution of Precision. Similar to GDOP, except elevation factors are ignored.

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.

ICW
Intracoastal Waterway. 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.

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.

Jacob’s 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.

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,(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.

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.

log
An instrument for measuring the speed or distance or both traveled by a vessel.

longitude
The distance in degrees east or west of the meridian at Greenwich, England.

LOP
Line of Position. 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.

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.

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.

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.

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.

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

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.

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!]

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.

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 pull
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.

quarter
The sides of a boat aft of amidships.

quartering sea
Sea coming on a boat’s quarter.

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 lirection
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 sights
Lights required to be shown on boats underway between sundown and sunup.

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.

SBAS
Satellite Based Augmentation System. An augmentation to GNSS that uses geostationary satellites to broadcast GNSS integrity and correction data, and additional ranging signals.

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.

sea room
A safe distance from the shore or other hazards.

seamanship
All the arts and skills of boat handling, ranging from maintenence and repairs to piloting, sail handling, marlinespike work, and rigging.

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.

SNR
Signal-to-Noise Ratio. The ratio of the magnitude of a signal to that of the noise (interference), often expressed in decibels.

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.

sransducer
A device that converts one type of energy to another, as a loudspeaker that changes electrical energy into acoustical energy.

stand-on vessel
That vessel which has right-of-way during a meeting, crossing, or overtaking situation.

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.

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.

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).

TD
Time Difference. 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.

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.

TRANSIT
Navy Navigation Satellite System. 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.

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.

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 ofUnicode 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].

UTC
Universal Time Coordinated. A time scale based on the rotation of the earth that is disseminated by most broadcast time services [compare with atomic time].

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.

WAAS
Wide Area Augmentation System. The Americas Satellite Based Augmentation System (see SBAS).

waypoint
A reference point on a track

Wide Area Augmentation System
(WAAS) The Americas Satellite Based Augmentation System (see SBAS).

WMM
World Magnetic Model. The WMM provides an estimated magnetic variation for any position on Earth. The WMM is a product of the United States National Geospatial-Intelligence Agency (NGA). The U.S. National Geophysical Data Center (NGDC) and the British Geological Survey (BGS) produced the WMM with funding provided by NGA in the USA and by the Defence Geographic Imagery and Intelligence Agency (DGIA) in the UK. Please refer to the following web page for additional information: http://www.ngdc.noaa.gov/seg/WMM/DoDWMM.shtml" http://www.ngdc.noaa.gov/seg/WMM/DoDWMM.shtml .

World Magnetic Model
(WMM) The WMM provides an estimated magnetic variation for any position on Earth. The WMM is a product of the United States National Geospatial-Intelligence Agency (NGA). The U.S. National Geophysical Data Center (NGDC) and the British Geological Survey (BGS) produced the WMM with funding provided by NGA in the USA and by the Defence Geographic Imagery and Intelligence Agency (DGIA) in the UK. Please refer to the following web page for additional information: http://www.ngdc.noaa.gov/seg/WMM/DoDWMM.shtml" http://www.ngdc.noaa.gov/seg/WMM/DoDWMM.shtml .

XTE
Cross Track Error. 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.

 
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