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Sailing Terminology and Definitions
AWA
(Apparent Wind Angle) The wind angle measured relative to the bow of the vessel.
AWS
(Apparent Wind Speed) The measured speed of the wind compensated for the movement of the boat.
BSP
(Boat Speed) The speed of the boat through the water.
BTW
(Bearing to Waypoint) The direction of travel towards a destination waypoint.
CTS
(Course to Steer) The calculated course to a destination, compensating for drift.
TRU
(True Wind Angle) Shown in the upper-left data field. The angle of the wind, compensated by the forward speed of the vessel.
TWA
(True Wind Angle) The angle of the wind, relative to the boat if it was stationary.
TWD
(True Wind Direction) The true direction of the wind relative to north.
TWS
(True Wind Speed) The speed of the wind, (if the boat was a stationary object).
True Wind Details
-TWD: (True Wind Direction) The true direction of the wind relative to north.
-TWA (True Wind Angle) The angle of the wind, relative to the boat if it was stationary.
-TWS (True Wind Speed) The speed of the wind, (if the boat was a stationary object).
DEVICES NEEDED TO PRODUCE TWD / TWA / TWS: gWind transducer and either a water speed source (paddle wheel/ultrasonic speed device) or a GPS system (chartplotter) connected to a NMEA 2000 Network.
NOTE: Boat must be moving for TWD / TWA / TWS information to be displayed.
VMG
(Velocity Made Good) is a term used in sailing , VMG indicates the speed of a sailboat towards (or from) the direction of the wind or an active waypoint.
VMG Details
- VMG – Velocity Made Good
- Waypoint VMG - Is a measurement of how fast a vessel is traveling, either toward or away from an active waypoint.
- Wind VMG - Is a measurement of how fast a vessel is moving, either toward the wind or away from where the wind is coming from.
Wind VMG:
Wind VMG-Is a measurement of how fast a vessel is moving, either toward the wind or away from where the wind is coming from.
Considerations:
- If the Wind VMG value is represented as a negative number, then the vessel is moving away from the wind.
- Wind VMG will be displayed as/in an “Overlay” box. It is found in the “Sailing” overlay function “Wind VMG”. It will be displayed as “Wind VMG” in an overlay box.
Devices Required to compute Wind VMG:
- Wind transducer connected (wired or wireless) to the NMEA 2000 network
- A Speed Source: Either GPS Speed Over Ground (SOG) or a Paddle Wheel (Water Speed) connected to the NMEA 2000 Network
- A display or instrument to present the information, such as a compatible chartplotter or GNX/GMI display
Waypoint VMG:
Waypoint VMG- Is a measurement of how fast a vessel is traveling, either toward or away from a waypoint.
Considerations:
- Waypoint VMG is 100% a function of the GPS system.
- If the Waypoint VMG value is represented as a negative number, then the vessel is moving away from the active waypoint.
- Waypoint VMG will be displayed as/in an “Overlay” number. It is found in the “Navigation” overlay function “Waypoint VMG”. It will be displayed as “Wpt. VMG” in the overlay box.
Devices Required to compute Waypoint VMG:
- Compatible chartplotter
- GPS Speed (SOG)
LAYLINE
Layline is an imaginary line extending from the objective (typically a racing mark) to indicate the point at which a boat should tack or gybe in order to just clear the mark on the correct side (weather side if upwind [tacking], leeward side if downwind [gybing]).
Layline Details
MARK: A point / waypoint that is designated as an turn on a route or a set position (waypoint) that your boat is intending to travel toward or round.
DEVICES NEEDED TO PRODUCE LAYLINES: Garmin chartplotter must be set as a Sailboat, gWind transducer, water speed source, GPS source, and select/create a waypoint or route and select “Route To”
TACKING
A sailing maneuver by which a vessel turns its bow into the wind, through the no-go zone, changing from a starboard tack to a port tack (or vice versa). Tacking is performed when the sailboat is sailing toward a point of sail that is generally considered toward the wind
JIBING / GYBING
Opposite of Tacking. This is when you are turning the boat away from the wind. Instead of the bow passing through the wind, the stern of the boat passes through the wind. Jiging / Gybing is generally performed when the sailboat is sailing downwind (wind is at the boats stern).
NO-GO-ZONE
A sailboat cannot sail directly into the wind, nor on a course that is too close to the direction from which the wind is blowing. The range of directions into which a sailing craft cannot sail is called the "no-go" zone.
TRUE WIND
The actual wind blowing. This is the wind felt when not moving.
APPARENT WIND
The wind generated by movement in combination with True Wind. If a vessel is not moving, it will only be feeling the effects of true wind.
In sailing, Apparent Wind is the actual flow of air acting upon a sail and is the wind as it appears to the sailor.
SET and DRIFT
Two terms used to describe the effect currents have on your boat.
SET is the direction in which the current is flowing.
DRIFT is the speed of the current.
Set and Drift Details
You need to take both of these into account when determining a route on the open ocean, flowing river, or body of water that is affected by wind driven waves.
DEVICES NEEDED TO DETERMINE DRIFT: A GPS source; typically it is a chartplotter with a built in GPS antenna or an external antenna.
Some sailors mistakenly believe that because they have a GPS to tell them what course to steer, they do not need to understand the effects of a current such as the Gulf Stream. This is simply not true. While your GPS will indeed display the straight line between you and your destination, it will not predict the effects of set and drift, which can change a favorable wind direction into a headwind.