Terminology

Any quantity, such as a force, velocity, or acceleration, which has both magnitude and direction, as opposed to a SCALAR which has magnitude only. Such a quantity may be represented geometrically by an arrow of length proportional to its magnitude, pointing in the given direction. [Dutch: vector]

A vector quantity equal to speed in a given direction. [Dutch: snelheid (in een bepaalde richting)]

The primary reference direction relative to the earth; the direction indicated by 000° in any system other than relative. True north is the direction of the north geographical pole; magnetic north the direction north as determined by the earth’s magnetic compass; grid north an arbitrary reference direction used with grid navigation. [Dutch: noord, noorden, N]

The direction of the north geographical pole; the reference direction for measurement of true directions. [Dutch: ware noorden, Nw]

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. The angle between magnetic and grid meridians is called GRID MAGNETIC ANGLE, GRID VARIATION, or GRIVATION. Called MAGNETIC VARIATION when a distinction is needed to prevent possible ambiguity. [Dutch: variatie, var]

The direction indicated by the north seeking pole of a freely suspended magnetic needle, influenced only by the earth’s magnetic field. [Dutch: magnetische noorden, Nm]

The angle between the magnetic meridian and the axis of a compass card, expressed in degrees east or west to indicate the direction in which the northern end of the compass card is offset from magnetic north. Deviation is caused by disturbing magnetic influences in the immediate vicinity of the compass. Semicircular deviation changes sign (E or W) approximately each 180° change of heading; quadrantal deviation changes sign approximately each 90° change of heading; constant deviation is the same on any heading. Deviation of a magnetic compass after adjustment or compensation is RESIDUAL DEVIATION. Called MAGNETIC DEVIATION when a distinction is needed to prevent possible ambiguity. [Dutch: deviatie, dev]

The direction north as indicated by a magnetic compass; the reference direction for measurement of compass directions. [Dutch: kompasnoorden, Nk]

A route is a predefined path or passage from one point to another. Routes generally use a series of Marks or Waypoints at each course change. Waypoints are Location Markers with specific Longitude and Latitude. The Route Legs between the Waypoints each have a specific Course and Distance.

A waypoint marks a specific location, coordinates, or Latitude and Longitude, often determined by GPS. A Waypoint could be considered the ending point of a Leg.

While calculating a Weather Routing the plugin will calculate the location of the boat for a given time interval (eg: 1 hr, 4hr, 6 hr or 12hr ) and an isochrone represents how far the boat willl sail in a given direction, based on the weather and boat conditions, for each successive time interval. Isochrones are like contour lines around the starting point. Think of them as showing an intermediate destination, and the calculated distancee traveled.

Wind speed and direction relative to the boat. Apparent Wind is measured in the frame of reference of the boat, which may be subject to boat movement through the water (propulsion by sails, engine, etc) and movement of the body of water itself (currents, tides, etc). Apparent Wind is relative to the boat.

Compass direction from which the wind is coming relative to the boat.

Apparent Wind Angle is expressed in angle to the bow of Ownship, in degrees to port or starboard of the Heading, as measured by the onboard wind instrument.

Wind speed relative to the boat as measured by the onboard wind instrument

Average Boat Speed through the water. (Trip Log / Trip Time)

Compass bearing to active waypoint measured from the current position.

Compass bearing to a waypoint measured from the previous waypoint.

Latitude and Longitude of the boat

Sometimes called Speedo Speed of the boat through the water as measured by the onboard speed transducer.

The course steered from the magnetic compass using adjustments for True, Variation and Magnetic Deviation values. True-Variation-Magnetic-Deviation-Compass (TVMDC) values.

Compass direction that the boat is moving through the water (HDG + Leeway). Note that the difference between CRS and COG is Current. CRS does not include the effect of current.

The course to steer to offset the effect of currents, wind and other factors.

Actual Compass direction that the boat is moving over the surface of the earth. (HDG + Leeway + Current) “The actual course you are moving along at the moment relative to the fixed land, meaning actual direction you travel regardless of the course steered and temporary variations in heading around this course. Things that cause COG to differ from heading include: current, leeway, poor helmsmanship, or compass errors.” Often derived from GPS.

The speed actually achieved which includes the effect or current set (direction) & drift (speed), wind and leeway and helmsman errrors. Same as SMG. Often derived from GPS.

Is the course actually steered which includes the effect of current set (direction) & drift (speed), wind and leeway and helmsman errrors. Note we distinguish COG (course over ground) from cmg (course made good), as one being present dynamic value, and the other being past. The phrase “course made good,” can be used to refer to a single track line or to the combination of several course changes between two points. If i sailed 1 mile north and 1 mile east, i made good a course of 045. Or, if i tried to sail course 200 but was being set between 10 and 20°, then i might end up “making good a course” of say 214. The distinctions between terms is not often critical, but may help to clarify some communications.

The speed actually achieved which includes the effect or current set (direction) & drift (speed), wind and leeway and helmsman errrors.

The perpendicular distance from the direct route (rhumb line or great circle) between two waypoints to the current position of the boat (POS)

Dead reckoning is the process of determining one’s present position by projecting known or estimated course(s) and speed(s) from a known past position, or predicting a future position by projecting known or estimated course(s) and speed(s) from a known present position. The DR position is only an approximate position.

Speed that the water is moving. This movement may be caused by a number of factors, including; tide, ocean currents, river flows etc.

An ECDIS is a computer-based navigation information system that complies with International Maritime Organization (IMO) regulations and can be used as an alternative to paper nautical charts. IMO refers to similar systems not meeting the regulations as Electronic Chart Systems (ECS)

An ENC is an official database created by a national hydrographic office for use with an ECDIS. An ENC must conform to standards stated in the International Hydrographic Organization (IHO) Special Publication S-57 before it can be certified as an ENC. Only ENCs can be used within ECDIS to meet the International Maritime Organisation (IMO) performance standard for ECDIS.

Wind speed and direction relative to the ground (same as landspeople’s true wind). Ground Wind direction is expressed in compass direction. Ground Wind speed and direction is also relative to boats anchored or moored and stationary relative to the earth. Ground Wind is used in weather forecasts and reports.

Wind direction relative to the ground (same as landspeople’s true wind). Ground Wind direction is expressed in compass direction.

Wind speed relative to the ground.

Compass direction in which the boat is pointed. The abbreviations HDT and HDM are typically used to distinguish between heading degrees true and heading degrees magnetic, whereas HDG does not infer either a true or a magnetic heading. Whether HDG displays true or magnetic values, will depend on sensor selection and system setup.

Heeling Angle in degrees of the port/starboard inclination of the boat. Heeling angle is associated with the boat’s lateral movement, or Leeway

Theoretical COG that will be achieved if the current conditions (TWD, TWS, TWA, SET, DFT, BSP, HEL etc), remain constant. There are port and starboard laylines that represent port and starboard tacks (or gybes). There are boat laylines, which emanate from the boat, and waypoint laylines, which emanate from the active waypoint. They are used to indicate when it is beneficial to tack or gybe.

Leeway is the angle between the HDG and the CRS and results from the lateral movement experienced by the boat as she moves forward through the water.. The empirical formula is that Leeway = -1 * k * Heel / BSP². The formula itself is often called into question, especially with planning hulls. The k value, which is boat specific, will vary according to crew numbers and boat loading.

Record of distance travelled

Compass direction of moving water (In the direction of the moving water). This movement may be caused by a number of factors, including; tide, ocean currents, river flows etc.

Speed that the boat is moving over the surface of the earth or ground.

Theoretical values for maximum BSP for a range of given TWSs and TWAs.

(BSP) Theoretical values for TWA and BSP for a range of given TWSs that result in the highest VMG. It is derived from the Speed Polars. https://sailzing.com/velocity-made-good-vmg/

A record of the ships position as it proceeds on its voyage.

Wind speed and direction relative to the surface of the water. Sailors sail in the interface between air and water, therefore mariners' True Wind is relative to water and different from landspeople’s true wind. True wind is perceived when the boat is stationary in the water, but moving with the tide or current; similar to the wind in the plane of reference of a stick floating down a river. True wind is not adjusted for current, tide or leeway, and that is how Ground wind differs.

Compass direction from which the wind is coming over the surface of the water.

True Wind angle is typically expressed as angle to the bow of Ownship. Note that mariners use the expression Wind angle relative to the bow in degrees to port or starboard of CRS (some instrument systems do not consider leeway in the calculation of TWA and in this case TWA is the wind angle relative to the bow in degrees to port or starboard of HDG).

Wind speed over the surface of the water.

Speed achieved directly toward the active waypoint. The value of VMC changes the longer the tack. VMC decreases the greater the angle to the mark, until on the layline where it turns to “0” and then starts getting negative because the distance from the mark is increasing.

Speed achieved directly towards, or away from, the TWD. The average value of VMG is an indicator of optimum sailing angle, and should be used as a general indicator, however the skipper should be using Target Boat speed to sail at the optimum tacking angel. https://sailzing.com/velocity-made-good-vmg/

ETA is not an accurate way to judge progress or performance in a tacking sailboat because it does not account for the greater distance sailed between waypoints. VMC (to Waypoint or Course) changes the longer the tack is (VMG decreases dramatically as the boat gets to the 'layline' for the mark, because of the increased angle from the mark) and VMG (to Wind) has similar problems because it is not relative to a destination. So these terms are not effective for sailing.

Calculates in advance how long it will take to tack (or jibe) a sailboat to a particular destination in particular wind conditions, including factors such as wind changes, currents, waves, boat polars, sail and boat bottom conditions. An approximation of performance. [From Sailtimer documents]. Tacking Time to Destination TTD may also provide a better measure of performance than ETA and VMG. Tacking performance is commonly judged by using Target boat speeds now.

The AIS class A “Turn rate” signal normally comes from a gyro or satellite compass. It’s not calculated by the AIS itself.

Heading rate is the rate of the heading which is typically derived from a magnetic compass. This is the absolute orientation of the boat.