Glossary

 

From ‘absolute bearing’ to ‘yaw’. If you are coming across marine terminology for the first time, our SIMRAD A-Z of online terms explains what they mean.

A-B

Absolute Bearing

    Absolute bearing refers to the angle between the magnetic north (magnetic bearing) or true north (true bearing) and an object.

AIS

    See Automatic Identification System

     

Anenometer

    An instrument used for measuring wind speed and direction. A fixed anenometer is often also called a Wind Sensor – data from this instrument can be displayed widely across the Simrad range.

Apparent Wind

    The aggregate term describing Apparent Wind Angle and Apparent Wind Speed.

Apparent Wind Angle

    The wind direction as it is detected on a moving platform like a boat. It is the vector that results from the combination of weather generated wind (True Wind) and the direction and speed of the boat through the air. Abbreviated AWA.

Apparent Wind Speed / AWS

    The wind speed as it is detected on a moving platform like a boat. It is the aggregate wind velocity that results from the combination of weather generated wind (True Wind) and the direction and speed of the boat through the air. Abbreviated AWS.

AWA

    See Apparent Wind Angle.

Automatic Identification System

    An automated tracking system that broadcasts vessel identification, position, speed and course data to assist marine traffic management and search and rescue among other purposes. Abbreviated AIS.

Azimuth

    An angular measurement between a celestial body like a star or satellite and the North, measured clockwise around the observer's horizon.

Bathymetric Chart

    A visual representation of the underwater terrain that uses Depth Contours and (typically) different shades of colour to indicate the shape of the water bed, such as you will find on the water areas of a maritime chart. 3D Bathymetric Charts visualise the same data in a three-dimensional representation to enhance understanding of the bottom shape.

Beam Sea

    A sea condition with waves at approximate right angles to the boat's heading.

Bear Away

    Turn a vessel away from the wind. Also known as Bear Down. 

Bear Up

    Turn a vessel away from the wind. Also known as Bear Down. 

Bearing

    The direction in degrees on a True North or Magnetic North compass rose between an object like a boat or observer, to another point see Relative Bearing) or to magnetic or true north (see Absolute Bearing). Abbreviated as BRG on marine electronics – but note this commonly refers to a Relative Bearing between the boat and a point such as a waypoint.

Bearing to Mark

    The Relative Bearing between a boat's current position and the chosen Mark. Abbreviated BTM.

Bearing to Waypoint

    The Relative Bearing between a boat's current position and the chosen Waypoint. Abbreviated BTW.

BRG

    See Relative Bearing.

BTM

    See Bearing to Mark.

BTW

    See Bearing to Waypoint

     

C-D

Cardinal Marks

    The four points of the compass – North, South, East and West

Celestial navigation

    Navigation by the position of the stars, sun and moon

Chartsum

    Calculation undertaken to ensure data is accurate

COG

    See Course Over Ground

Course

    Planned route to a destination, Waypoint or Mark

Course Bearing

    The Course Bearing is the bearing to remain on a leg of a course

Course Over Ground

    The direction of progress of a vessel, with respect to the Earth's surface. 

Cross Track Distance

    Defined as the closest distance from the proximity station, to the planned navigation route

Cross Track Error

    The distance the vessel is to one side or the other of the course between two waypoints

CTS

    See Course to Steer

Dead Reckoning

    A method of navigation estimating a vessel's position from the distance run measured by the log and course steered

Depth Contour

    A line that joins points of identical depth

DR

    See Dead Reckoning

DTG

    Distance to Go - When navigating to a Waypoint, DTG indicates the remaining distance from your present position to the next Waypoint

DTM

    Distance to Mark

DTW

    Distance to Waypoint

E-F

ECDIS

    Electronic Chart Display and Information Systems – a standard set by the IMO to govern electronic navigation equipment as an alternative to paper charts. Typically applicable for commercial vessels.

EPIRB

    Emergency Position Indicator Radio Beacon

ETW

    Estimated time to Waypoint

Fathom

    A measurement of 6 feet or 1.8 metres

G-H

GLONASS

    GLONASS is a Russian space-based satellite navigation system operating as part of a radionavigation-satellite service. It provides an alternative to GPS and is the second navigational system in operation with global coverage and of comparable precision

GNSS

    Global Navigation Satellite System

GPS

     

Green to Green

    Vessels moving in the opposite direction on their starboard sides

Hard

    Section of shoreline suitable for mooring or hauling out

Heading (HDG)

    The direction in which the nose of the vessel is heading - not necessarily the same as the direction the vessel is actually moving

Head Sea

    A sea in which the waves are directly opposing the motion of the vessel

Heavy Weather

    Combination of high seas and rough winds making for dangerous passage

I-J

IMO

    International Maritime Organization, the body based in London that sets internationally adopted maritime standards and laws like the ColRegs

Inshore

    Water that is typically close to or within sight of the shore

K-L

Knot

    Unit of speed equivalent to 1 nautical mile - 1.8520km or 1.1508 mi per hour

Lateral system

    A system of aids to navigation whereby characterisitcs of buoys and beacons indicate the sides of a channel or route

Latitude

    The angular distance of a place north or south of the earth's equator, or of the equator of a celestial object.  Expressed in degrees and minutes

     

Laylines

    A straight line, or bearing, extending from a mark or waypoint to indicate the course the vessel should take to pass to the windward side of the mark

Lay to

    To bring a vessel into the wind and hold her stationary

League

    A measurement of three nautical miles

Leg

    A segment of a route between two waypoints

Longitude

    The angular distance of a place east or west of the Greenwich meridian.  Expressed in degrees and minutes

     

M-N

Magnetic bearing

    An absolute bearing using magnetic north

Magnetic North

    The direction towards the North Magnetic Pole

Magnetic variation

Mark

    Typically, a featured point on a chart that hasn't been set by a user. Common examples include navigation, danger or sailing buoys.

MFD

    Mutlifunction Display

MOB

    Man Overboard, an emergency situation requiring assistance

Nautical mile

    A unit of length approximating to one minute of arc of latitude andloong any meridian arc

NFU

ND

    NoDrift instruction on autopilot

O-P

Onshore

    A wind that is blowing from the sea towards the land.

Point

    A unit of bearing equal to 1/32 of a circle - or 11.23 degrees

Polar %

    Boat speed predictions across a variety of wind speeds

Q-R

Quartering Sea

    Seas approaching a vessel from between 105˚ and 165˚ to port or starboard

Radar

Relative Bearing

    The horizontal direction in degrees (True North or Magnetic North) from an object like a boat or observer, to another point see Relative Bearing) or to magnetic or true north (see Absolute Bearing). Abbreviated as BRG on marine electronics – but note this commonly refers to a Relative Bearing between the boat and a point such as a waypoint.

RNC

    Raster Navigation Charts - a scan of a paper chart

    See C-MAP charts

Reaching

    Driving the vessel across the wind

S-T

Set

    The direction toward which the current flows

Set HDG

    Set Heading instruction on autopilot

Sextant

    A navigational instrument used to measure a ship's latitude

Shift tides

    Sighting the position of the sun abd moon using a sextant, referencing a nautical almanac to determine the location and phase of the moon and calculating the relative effect of the tides on the navigation of the vessel

Shoal

    Shallow water presenting a hazard to navigation

Shoal draught

    An especially shallow draught of a vessel - capable of negotiating unusually shallow water

Slack tide

    The period between rising tie or falling tide - or falling tide and rising tide

Slip

    A place for a vessel to launch or moor

SOG

    Abbreviation od Speed Over Ground, the speed of the vessel relative to the earth

Sounding

    Measuring the depth of the warer

     

Springs

    Big tides caused by the alignment of the moon and the sun

STW

    Abbreviation of Speed Through Water

Track (TRK)

    The path of the vessel

Trim

    The relationship of a ship's hull to the waterline

    See our Instruments page

True Bearing

    An absolute bearing using true north

True North

    The direction of the geographical North Pole

TW

    True Wind

TWA

    True Wind Angle

TWD

    True Wind Direction

TWS

    True Wind Speed

U-V

Upbound

    A vessel travelling upstream

UTC

    Coordinated Universal Time

Vector Charts

    Charts displayed by the plotter from stored data points

    See C-MAP Reveal

W-X

Waft

    Signal flag on a vessel

Wake

    Turbulence behind a vessel.

Waypoint

Weather side

    The side of the vessel exposed to the wind

Weigh Anchor

    To heave up or lift the anchor preparatory to sailing

Wheelhouse

    Location on a vessel where the sheel or controls are situated, also called the pilothouse or bridge

Wind Sensor

    See Anenometer

Wind-over-tide

    Sea conditions with a tidal current and a wind in oppositite directions resulting in short heavy seas

Windage

    Wind resistance of the boat

Windward

    In the direction the wind is coming from

XTE

    See Cross Track Error

Y-Z

Yaw

    A vessel's rotational motion around a vertical axis