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B&G Glossary

TWA, TWD, VMG, VMC? If you're stuck on an acronym or need to know the meaning of a word, look it up in our handy Glossary below...




AIS (Automatic Identifcation System) is used for vessel tracking that allows boats to transmit and receive information from other vessels and base stations to provide data including name, call sign, boat type and position.

Apparent Wind

Apparent Wind is the wind that you feel on the boat when sailing - it is a combination of the wind blowing across the water's surface (the True Wind) and the speed of the boat (Boat Speed).

See also:

  • Apparent Wind Speed
  • Apparent Wind Angle

Apparent Wind Angle

In sailing, the apparent wind is the actual flow of air acting upon a sail. This can be experienced on a calm day - if you stand still there is no wind, but if you begin to run forward you can feel wind rushing in your face- this is an example of apparent wind.

Apparent Wind Angle is the angle of this wind relative to the bow of the boat.


AutoCal refers to automated calibration routines available on some B&G systems which make complex calibration procedures quick and easy.

Automatic Tidal Offset

A feature of Insight Genesis, which automatically adjusts the depth reading of coastal sonar logs based on known tide and current conditions.


See Apparent Wind Angle


See Apparent Wind Speed


Bathymetric charts

Bathmetric charts are a visual representation of underwater terrain; they show contours of the area beneath water in a similar way to how a topographic map shows the lay of the land above water.

Boat Speed

Speed at which the boat is travelling through the water along its current course

Bonded Display

Glass bonding leaves no room for encroaching air or moisture within a display unit, this removes any chance of misting or condensation within screens.

Broadband Radar™

Unlike traditional pulse radar, Broadband Radar™ continuously transmits and receives data using FMCW Technology ( Frequency Modulated Continuous Wave). This means that the phenomenon seen with pulse radar, where the area closest to the boat is not able to be monitored, does not exist with Broadband Radar.
This results in the ability to monitor targets right up to the bow of the boat, which is essential for iceberg fields and busy ports alike.
Broadband Radar is a technology exclusive to B&G and its sister companies Lowrance and Simrad Yachting.



Bearing to Mark


Bearing to Waypoint



Cartography in the modern sense tends to refer to digital charting, which is used via a chartplotter or PC.
Digital cartography used with B&G systems include Navionics and C-MAP. 


A basic Chartplotter integrates digital/electronic charts with GPS positioning data. Most modern Chartplotters are also an MFD


The actual path travelled by a vessel from one point to another


Course is a planned route to a destination, Waypoint or Mark.


A current in its basic form is the strength and direction of flow within a liquid.
In oceans this can be effected by many factors including gravitational pull, breaking waves, temperature differences, changes in salinity and general topography of the seabed.


Czone is a digital switching system that provides full integration with your marine electronics systems. Turn on lights, flush out freshwater systems or check grey water levels right from your chartplotter screen.



Distance to Mark


Distance to Waypoint



European Geostationary Navigation Overlay Service (EGNOS) is a Satellite Based Augmentation System, very similar to WAAS but supplying correction data to Europe.


Estimated Time of Arrival (at a Waypoint)



B&G's legacy proprietary network protocol used on H3000 and WTP3 systems.


Frequency Modulated Continuous Wave - the technology that enables B&G's Broadband Radar models to perform using a fraction of the transmission power (millwatts vs. kilowatts) of traditional pulse radars.



A global navigation system that is currently under development by the European Union.


Global Navigation Satellite System is a global system, which complements GPS and is the only other system that can be used across the world. It is comprised of 24 satellites and is a Russian-based service.

Ground Wind

Ground wind is the speed and dlirection of the wind referenced to land.

Ground Wind is often used by sailors in a strong tidal current when trying to anticipate what the wind will be like when the tide changes.

Weather forecasts provide Ground Wind. If sailing in tidal areas the navigator should be aware of the additional "Tide Wind" effect and compensate for it in their decision making. For example, if the forecast is for 18 knots of wind, 2 knots of tide could be the difference between 16 and 20 knots of True Wind.


HALO Radar

B&G's new Pulse Compression Radar. 


The current direction in which a vessel is pointing. It is the angle between North and the bow of the boat.

Heading on Opposite Tack

This function provides the navigator with the Heading the boat will be sailing on if it is sailed to the same wind angle on the opposite tack.

For example if the boat is sailing upwind on Starboard tack in a Northerly wind (000 degrees) and the True Wind Angle is 45 degrees, the Heading would be 315 degrees. The Heading on Opposite Tack would be 045 degrees.


The Heel of the boat (the extent to which it tips or leans sideways) is often the result of the force of wind on the sails. Most of this wind is transferred into forward movement, any excess is transferred as sideways movement, some of which leads to heeling.
The transference of weight on the boat can also cause heeling, which can be used as an advantage when racing. However it is a delicate balance as a boat that heels too much will sail less efficiently.

HV Technology

HV Technology gives maximum contrast, optimum backlighting and no condensation due to bonded glass LCD displays. This unique technology provides incredible viewing angles and sharp, clear information.




A straight line, or bearing, which extends from a mark to indicate the course a boat should sail with one tack to pass to the windward side of the mark.


Leeward is the direction downwind from a specified position. Seen the side of the boat on which the force of the wind is not felt.


The sideways slip to Leeward of a boat travelling through the water, most obviously experienced when sailing upwind. Typical values of leeway are 3-5 degrees, but can be more or less depending on the type of boat, the heel angle and the sea state.

Line Bias

The end of a racing start line which is closest to the wind. Can be expressed as an angle ("Port end is biased by 3 degrees") or a distance, usually boat-lengths, ("Port end is biased by 2 lengths").

Line Bias is just one consideration of where to start on a line - others include tide, first leg strategy, other competitors etc.


Loadcells are sensors that detect force and convert it to an electrical signal that can then be viewed and recorded.

Loadcells are particularly useful for replicating settings tack-to-tack and day-to-day, e.g. Forestay tension. They are also widely used on larger yachts for monitoring safe working loads (SWL) of rigging and other components.


Magnetic Variation

Magnetic variation is the angle between magnetic north as shown by a compass and True North.
Magnetic Variation differs both from place to place and with the passage of time. Metals such as Iron Ore in the Earth's crust may contribute strongly to this phenomenon.


A mark is a point that sailors will travel around in a race, it is often shown by an inflatable buoy.


An MFD or Multifunction Display Unit integrates a Chartplotter with further functions such as Radar, Echosounder, AIS, instrument data, Autopilot control, entertainment and much more.
An MFD is often the control centre of the boat’s marine electronic systems.


MOB or Man Overboard is an emergency situation in which a person has fallen from a boat or ship into the water, usually requiring assistance.

The term is also a reporting function on a VHF or AIS that records the time and position of an incident as a waypoint for navigation and / or to raise the alarm. 




The NMEA - National Marine Electronics Association created a uniform interface standard for digital data exchange between different marine electronic products back in the early eighties.
The NMEA 0183 and NMEA 2000 protocols are now among the most common forms of marine network.


Optimum Routing

Optimum Routing or the best theoretical route to the finish line is not just about the fastest route, it is also about avoidance of hazard.

Deckman allows you to route around strong wind conditions by adjusting the boat speed in the Polar Table - for example entering data to suggest the boat does 0.1 knots in 50 knots of wind would effectively route you around the strongest winds.


Performance Wind Filter

The Performance Wind Filter is a significant element of B&G’s highly accurate wind calculation. The raw wind data from the sensors is processed by the Performance Wind Filter which includes user level True Wind Corrections, Heel/Trim angle correction algorithms and (for H5000 Hercules and Performance Systems equipped with the 3D Motion sensor) the PWF also calculates and corrects for induced wind caused by the boat’s motion in waves. The output is highly accurate and stable True and Apparent wind data.


Active sonar creates a pulse of sound, often called a "ping", and then listens for the echo of the pulse.

Pitch Rate

The rate at which the bow of the boat moves up or down

Polar %

Boat speed predictions across a variety of wind speeds.

Polar Boat Speed

Boat speed predictions across a variety of wind speeds.

Polar Speed

Boat speed predictions across a variety of wind speeds.

Polar Tables

Tables of target angles and speeds for use when trying to maximise VMG, these are also often seen as graphs to help with visualisation.


Roll Rate

The rate at which a boat is heeling.


Sailing Wind

Angle and direction of the wind as measured from shore.

Sailing Time

Sailing Time functions display the Time To Waypoint, Distance To Waypoint and Estimated Time or Arrival at waypoint using the layline calculations. This ensures a realistic value for these functions rather than relying on a feature designed for a power boat.

Sea Breeze

An Onshore or Sea Breeze is cool air, which moves inland due to the differences in temperature and pressure between the cool air above the sea and the warmer air above nearby land.

Sea State

Sea state is a general description of the conditions at sea at a certain time and location.
Wind speed and wave height are major factors in deriving sea state, which also depends on current, coastal topography, the depth and nature of the seabed.
The Beaufort Sea State Code is often quoted in respect to sea state, It is a scale that can be used to give a succinct description of sea conditions.


Speed Over Ground. This differs from boat speed- so for example if your boat is stationary in the water, it may still be moving in relation to the land due to current and wind etc.


Target %

The goal or target speed set to achieve sailing upwind or downwind for a given wind speed.

Target Boat Speed

The goal or target speed set to achieve sailing upwind or downwind for a given wind speed.

Target Speed

The goal or target speed set to achieve sailing upwind or downwind for a given wind speed.


The rise and fall of sea levels caused by the effects of the gravitational pull from the moon, the sun and the rotation of the Earth.
Tides are described as being either high or low, which will effect how deep or shallow water will be near land.


The process of positioning and adjusting the angle of sails or “Trimming” to catch the wind in the most efficient way.
This procedure is normally undertaken in response to wind changes, such as direction and strength.

True North

The direction across the surface of the earth that leads toward the geographic North Pole.


Time to Go, this can be to a mark, waypoint or destination


Time to Mark


True Wind Angle



A measure of speed towards a specific Mark or target, gives actual progress towards a specific point on a course. Often referred to as "VMG to Waypoint". If you see "VMG" on a GPS unit, it is really VMC.


A measure of your speed towards the wind. A boat sailing at 90 degrees to the wind has a VMG of zero, a boat sailing at 45 degrees to the wind at 10 knots Boat Speed has a VMG of just over 7 knots.


B&G's touchscreen chartplotter for club racing and cruising sailors, available in 7, 9 and 12". 




Wide Area Augmentation System (WAAS) is a Satellite Based Augmentation System - more simply described as an "add-on" to the GPS system developed to improve accuracy and availability. WAAS covers the USA.

Wave Technology

Wave Technology as used in the WTP3 system increases accuracy of data by eliminating the effects of boat motion.


Waypoints are a specific point oh the Earth's surface. They are given as coordinates that reflect latitude and longitude.
In sailing waypoints are often used to build a route to a specific destination or to find a specific point or mark.

Wind Gradient

Wind Gradient refers to the variation of wind over either horizontal or vertical distances.
At water level, wind speed is almost zero, as the closer to the water, the slower the wind; this is wind gradient. Wind Gradient is caused by friction between the wind, water surface and waves.

Wind Shear

A change in wind speed or direction with variation in height.


Windward is the direction upwind from a specified position.



Cross Track Error - the distance you have strayed from the straight line route between start and finish points on a route. 


Yaw Rate

Yaw rate is the rate of movement either left of right in the direction in which a boat is facing.



Our touchscreen chartplotter, featuring a SolarMax HD, sunlight viewable screen, intuitive keypad and full networking capabilities.