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  • Glossary

Glossary

To be used in conjunction with the below courses:

Day Skipper/Watch Leader

RYA Yachtmaster/Coastal Skipper courses

Select the letter of the alphabet from below to find the abbreviations and terms you need to be familiar with. All links in the definitions and information below lead to live documents on the internet and may not be managed by the RYA.

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

If you feel other useful definitions should be included within this glossary, please email:

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A

Also known as: Aft or stern

What is it? The aft is the very back of a boat.

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Also known as: Automatic Identification System

What is it? A VHF based system that allows vessels to transmit information about themselves including MMSI number, callsign, name, position and course over ground and speed over ground. Vessels fitted with an AIS receiver can overlay this information on electronic charts and radar displays.

Where does it apply? The IMO SOLAS requires AIS to be fitted aboard international voyaging ships with 300 or more gross tonnage, and all passenger ships regardless of size. Small vessels such as pleasure craft are not required to have AIS installed.

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Also known as: Automatic Radar Plotting Aid

What is it? A marine radar with automatic radar plotting aid (ARPA) capability is an anti-collision radar. The system is able to constantly monitor a number of objects, plot their speed and course, and present these as vectors on a display screen. This is updated with each sweep of the antenna.

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Also known as: Autoroute

What is it? A generic term to describe the function of an electronic navigation system generating a suggested route based on a start and end waypoint being entered. The parameters that are used to create a route vary between manufacturers and, in every case, routes must be checked and amended as necessary by the navigator to ensure it is safe to use.

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B

Also known as: Bearing

What is it? An angle from 000° to 359°, where: 000° = north, 090° = east, 180° = south, 270° = west

Also known as: Bow

What is it? The front of the boat is called the bow. Knowing the location of the bow is important for defining two of the other most-common terms: port and starboard

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C

Also known as: Chart datum

What is it? A chart shows the lowest tide you are likely to meet, and the tide tables give the amount of water above that level (chart datum) for each high and low water.

Also known as: Chart depth

What is it? Charted depth is measured from the chart datum to the seabed.

Also known as: Charted heights

What is it? Charted heights, such as heights of lights or clearance under bridges, are always measured from Mean High Water Spring (the highest average tide height).

Also known as: Chartplotter or Plotter

What is it? A common name to describe an electronic navigation system which displays an electronic chart with a GNSS derived position marked for the vessel position.

Also known as: COLREGS or IRPCS (The International Regulations for Preventing Collisions at Sea)

What is it? Details the regulations governing collision avoidance, sound signals, lights and shapes and internationally recognised distress signals for all ships.

Where does it apply? To all vessels on the high seas and in all waters connected navigable by seagoing vessels.

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Also known as: Course also known as heading

What is it? May be used to describe the direction in which the vessel is being steered or is to be steered.

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Also known as: Shaping a course or course to steer

What is it? The estimated course that a vessel should steer in order to arrive at a specific waypoint, taking into consideration the effects that wind and tide will have on it.

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Also known as: Course over ground or course made good

What is it? The direction in which a vessel has travelled with the effects of current, wind, and skipper.

Also known as: Compass

What is it? Measures your orientation to the earth’s magnetic pole.

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Also known as: Course made good or course over ground

What is it? The direction in which a vessel has travelled with the effects of current, wind, and skipper.

Also known as: Cross track distance or cross track error

What is it? The distance away from the intended or reference route. An alarm can be set so that corrective action can be taken.

Also known as: Cross track error or cross track distance

What is it? The distance away from the intended or reference route. An alarm can be set so that corrective action can be taken.

Also known as: Crowdsourced

What is it? Private entities can participate in increasing our knowledge of the ocean by sharing depth measurements from navigation instruments whole out at sea. Known as crowdsourced, this work can help identify uncharted features such as seamounts, canyons etc.

D

Also known as: Dead reckoning

What is it? Dead reckoning is a position deduced from a course steered and a distance run. It makes no allowance for tidal set and drift or leeway.

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Also known as: Depth

What is it? The depth of water is measured from the height to the seabed.

Also known as: Depth sounder

What is it? Measures the depth of water from its location, usually using ultrasonic signals which are reflected from the seabed. The calculated value can be displayed with an added offset to set the reading to represent depth from a particular datum such as under the keel or propellors, or depth from the waterline.

Also known as: Deviation

What is it? Magnetic compass error caused by presence of magnetic objects.

Also known as: Drying height

What is it? Drying height is the vertical distance of the seabed that is exposed by the tide above the seawater level at the lowest astronomical tide.

E

Also known as: Echo sounder

What is it? The echo sounder transmits sound pulses downwards into the water by a transducer. The echo reflected from the bed is received by the echo sounder which gives you an estimation of the depth of water.

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Also known as: Electronic chart

What is it? Any digital chart that is not approved as an ENC (Electronic Navigational Chart). They may be in vector or raster format.

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Also known as: ECDIS – Electronic Chart Display and Information System

What is it? Electronic chart systems used on commercial ships, approved by national authorities under international standards.

Where does it apply? It is not enough for a vessel to simply have an ECDIS on board. It must be compliant with SOLAS regulations and have appropriate electronic charts for the vessel’s intended voyage.

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What is it? Electronic equipment such as radar, GPS receivers, chart plotters, ECDIS systems, gyro, ARPA, echo sounder etc.

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Also known as: Electronic navigation charts or Vector charts, known as a smart chart.

What is it? The most common type of electronic chart used on ECDIS and integrated with other data such as GPS, radar, route planning, heading, speed and draught. The benefit of having layers of information the user can zoom in for more detail.

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Also known as: eNavigation

What is it? The aim of the International Maritime Organisation’s (IMO) eNavigation strategy is aimed at enhancing navigational efficiency and safety by presenting seafarers with the necessary information at the appropriate time. Used intelligently it adds to the pleasure of boating.

Also known as: Estimated position

What is it? Estimated position is the best-possible estimate of a present or future position. It is based on a distance run from a known position with an allowance made for both leeway and the tidal set and drift.

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Also known as: EPIRB

What is it? Safety device carried by a vessel to alert search and rescue services. It transmits a distress signal via satellite to Maritime Rescue Co-ordination Centres, most have built-in GNSS to provide a position. It must be registered to a vessel, and it has a longer battery life than PLB.

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F

Also known as: Fix

What is it? When using electronic navigation aids, we know where we are all the time. Without the use of satellites, a fix can be found be using a compass, radio direction bearings, depth sounding, and transits.

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G

Also known as: GALILEO

What is it? European satellite navigation system

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Also known as: GMDSS

What is it? A worldwide system for emergency signalling and communication for vessels at sea.

Also known as: Global Navigation Satellite System

What is it? A system of satellites that provides a GNSS receiver with the means to create a fix using signals from multiple orbiting satellites. It determines, longitude, latitude, altitude, and elevation with great accuracy.

Where does it apply? Globally

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Also known as: Global Navigation Satellite System

What is it? A Russian GNSS system.

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Also known as: GPS

What is it? A navigation system that uses satellites to determine a location on Earth. Satellites constantly send out signals, when using four or more of these signals a GPS receiver can calculate its location.

Where does it apply? Globally

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Also known as: Ground track

What is it? The direction the vessel has moved over the seabed.

Also known as: Gyro

What is it? A gyro compass in navigation is an instrument which makes use of a continuously driven gyroscope to accurately seek the direction of true (geographic) north. Whereas a compass measures your orientation to the earth’s magnetic pole.

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H

Also known as: Heading

What is it? The direction in which the vessel is pointing at any given moment.

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Also known as: Head-up display

What is it? The top of the navigational display screen follows the bow of the vessel. The vessel will always point to the top of the screen and the displayed chart or radar image will rotate around the vessel position as the heading changes.

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Also known as: Height of tide

What is it? Height of tide is always measured from the chart datum.

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Also known as: HAT

What is it? Highest astronomical tide is used for vertical clearances, e.g. under bridges.

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Also known as: Horizontal datum

What is it? Horizontal datums are used to measure latitude and longitude on the surface of the Earth.

Where does it apply? Datums vary depending on where you are.

Also known as: HDoP

What is it? A factor in determining the relative accuracy for GPS. The higher the figure, the less confidence in the precision of the position. HDoP below two indicates an excellent precision. HDoP over seven means the position should not be relied upon.

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  • GPS – Global Positioning System

Also known as: The Coastguard

The Coastguard coordinates all maritime search and rescue (SAR) operations in the UK through a network of coastguard stations, operating 24 hours a day.

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I

Also known as: International Certificate of Competence or International Certificate of Competence for Operators of Pleasure Craft

What is it? A certificate of competence for pleasure craft issued by countries which are members of the United Nations Economic Commission for Europe (UNECE). Countries taking part in this scheme accept ICCs issued by other participating countries as sufficient evidence of competence within their jurisdiction.

Where does it apply? Within countries of the United Nations Economic Commission for Europe.

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Also known as: International Maritime Organisation

What is it? A specialised agency of the United Nations with responsibility for the safety and security of shipping and the prevention of pollution by ships.

Where does it apply? Globally

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Also known as: International Hydrographic Organisation

What is it? The IHO works to ensure that all the world’s seas, oceans, and navigable waters are surveyed and charted. Hydrographic maps are a valuable source of information both above and below the water.

Where does it apply? Globally

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K

Also known as: Knot, knt

What is it? One nautical mile per hour or a deliberate compilation made in a rope.

L

Also known as: Latitude

What is it? The distance from the equator, expressed as an angle, measured in degrees at the centre of the earth.

Also known as: Leeward

What is it? Away from the wind, the side facing away from the wind.

Examples: "The leeward side of the of the vessel"

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Also known as: Leeway

What is it? The amount the vessel is being pushed sideways by the wind while underway. It is one of the factors to consider when shaping a course

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Also known as: Longitude

What is it? The distance from the prime meridian, expressed as an angle, measured in degrees at the centre of the earth.

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Also known as: Longitude

What is it? Lowest astronomical tide is often used for chart datum.

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M

Also known as: Magnetic North

What is it? It is the direction that a compass needle points to as it aligns with the Earth’s magnetic field.

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Also known as: MAIB

What is it? The MAIB investigates marine accidents involving UK vessels worldwide and all vessels in UK territorial waters.

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Also known as: International Convention for the Prevention of Pollution from Ships

What is it? International convention published by the International Maritime Organisation (IMO) covering the prevention of the pollution of the marine environment by ships.

Where does it apply? Worldwide with significant variations depending in size and type of vessel and geographical location.

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See also: Small Commercial Vessels and Pilot Boat Code

Also known as: Meridian

What is it? An imaginary line running north to south that is used as a reference line.

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Also known as: Mean High Water Neaps

What is it? Mean High Water Neaps is the average height of all the neap high waters.

Also known as: Mean High Water Springs

What is it? Mean High Water Springs is the average height of all the spring high waters.

Also known as: Mean Low Water Neaps

What is it? Mean Low Water Neaps is the average height of all the neap low waters.

Also known as: Mean Low Water Springs

What is it? Mean Low Water Springs is the average height of all the spring low waters.

Also known as: Miles (M)

What is it? Capital M = Miles. In official nautical publications, M is used to denote nautical miles. In unofficial publications and many electronic displays, other abbreviations may be seen such as NM. On small-scale paper charts, one minute of latitude is used as an approximation of a nautical mile and is officially called a sea mile.

Also known as: MFD

What is it? A screen that can be used to display information from multiple sources

N

Also known as: Nautical mile

What is it? A standardised distance of 1,852 metres.

Also known as: Neap tide

What is it? The gravitational pull of the moon and sun at its weakest gives rise to neap tides and a smaller range. Spring tides follow approximately seven days after neap tides, then approximately seven days later it is neaps again, and so on.

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Also known as: North-up display

What is it? North will always be at the top of the screen. The screen will not move; the vessel will move around the screen.

P

Also known as: Nautical paper chart

What is it? Nautical charts provide hydrographical, nautical, and topographical information to the sea goer. The amount of information provided on a nautical chart depends on its scale. The larger the scale, the more information is provided.

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Also known as: PLB

What is it? Safety device carried by you to alert search and rescue services. It transmits a distress signal via satellite to Maritime Rescue Co-ordination Centres, most have built-in GNSS to provide a position. It has a shorter battery life than EPIRB and is smaller in size.

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What is it? Extract from Merchant Shipping (Vessels in Commercial Use for Sport or Pleasure) Regulations.

"pleasure vessel" means:

(a) any vessel which at the time it is being used is:

(i) (aa) in the case of a vessel wholly owned by an individual or individuals, used only for the sport or pleasure of the owner or the immediate family or friends of the owner; or

(bb) in the case of a vessel owned by a body corporate, used only for sport or pleasure and on which the persons on board are employees or officers of the body corporate, or their immediate family or friends; and

(ii) on a voyage or excursion which is one for which the owner does not receive money for or in connection with operating the vessel or carrying any person, other than as a contribution to the direct expenses of the operation of the vessel incurred during the voyage or excursion; or

(b) any vessel wholly owned by or on behalf of a members' club formed for the purpose of sport or pleasure which, at the time it is being used, is used only for the sport or pleasure of members of that club or their immediate family, and for the use of which any charges levied are paid into club funds and applied for the general use of the club; and

(c) in the case of any vessel referred to in paragraphs (a) or (b) above no other payments are made by or on behalf of users of the vessel, other than by the owner.

In this definition "immediate family" means:

in relation to an individual, the spouse or civil partner of the individual, and a relative of the individual or the individual's spouse or civil partner; and "relative" means brother, sister, ancestor or lineal descendant;

Key sections referenced in the course:

Referenced in "RYA Commercial Regulations for Small Vessels" (G105) on page 15

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Also known as: Port

What is it? Port is always the left-hand side of the boat when you are facing the bow

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Also known as: Greenwich Meridian

What is it? The meridian which passes through the Greenwich Observatory in London. It is the starting point (0°) for the measurement of longitude E and W.

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R

Also known as: Radar

What is it? Marine radar is an electronic device that measures the bearing and distance of solid objects relative to your current location. It works by sending out a radio signal. When the signal hits an object, it gets reflected back to the radar which can then calculate a rough estimate of the object.

It is a versatile piece of equipment that can be used for navigation, collision avoidance, and weather monitoring.

There are two versions: an S-band and an X-band. Leisure-sector radars usually use the 10GHz X-band radars.

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Also known as: Range

What is it? A distance, typically to an object from your own position or the distance a lighthouse light can nominally be seen.

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Also known as: RNC – Raster navigational chart

What is it? Exact electronic copies of paper charts. There is no intelligence or extra data (layers) to zoom down to.

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Also known as: Rise of tide

What is it? The rise of tide is how much the water has risen from low water for that day.

Also known as: Route

What is it? A number of waypoints linked together.

Also known as: Rubber banding

What is it? A technique for manually crating a safe route using electronic chart displays. The principle is to put a start and end waypoint in first, then zoom in and go through the route to place additional waypoints as if you were stretching a rubber band around pins.

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S

Also known as: SART

What is it? A distress-signalling device that displays a series of dots on an X-band radar display within range. As the vessel receiving the SART’s signal draws closer to the SART, the dots become arcs and then solid rings.

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Also known as: Satellite based augmentation system (SBAS)

What is it? This provides augmentation information via satellite to GNSS receivers to reduce errors. Examples are the Wide Area Augmentation System (WASS) from the US or the European Geostationary Navigation Overlay Service (EGNOS).

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Also known as: Sea mile

What is it? One minute of latitude

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Also known as: Set and drift

What is it? The direction and speed of current.

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Also known as: Shaping a course or course to steer

What is it? The estimated course that a vessel should steer in order to arrive at a specific waypoint, taking into consideration the effects that wind and tide will have on it.

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Also known as: Speed over ground (SOG)

What is it? The speed of the vessel’s movement traced over the seabed as opposed to through the water.

Also known as: Safety of Life at Sea, International Convention for the Safety of Life at Sea

What is it? An international convention published by the International Maritime Organisation (IMO) concerning safety at sea.

Where does it apply? Worldwide although most sections only apply to merchant shipping. Chapter V applies to all vessels.

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Key sections referenced in the course:

Liferaft equipment packs – SOLAS A and SOLAS B

Liferafts not built to the SOLAS standard may be accepted on small commercial vessels, eg; ISO 9650 standard is accepted. In many cases the acceptance is conditional on additional equipment being carried in a grab bag to bring the equipment level up to the level of a SOLAS A or B liferaft.

Also known as: Spring tide

What is it? The gravitational pull of the moon and sun combine (line up) to create spring tides and a larger range. This happens every two weeks during a new moon or a full moon.

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Also known as: Starboard

What is it? Starboard is always the right-hand side of the boat when you are facing the bow.

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Also known as: Stern or aft

What is it? The stern is the very back of a boat.

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T

Also known as: Tidal range

What is it? The difference between high tide and low tide is known as tidal range. Tides are the rise and fall of sea levels caused by the gravitational forces exerted by the sun and moon and the rotation of Earth.

Where does it apply? Tidal range depends on time and location.

Also known as: Tidal stream

What is it? Tidal streams are described by tidal set and drift. Tidal set is the direction of the current and drift is the speed of the current measured in knots.

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Also known as: Transit

What is it? When two objects you can see line up.

Also known as: True North

What is it? It is the direction that points directly towards the geographic North Pole. This is a fixed point on the Earth’s globe.

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U

Also known as: Under way

What is it? It is a definition from the International Regulations for Prevention Collisions at Sea and means when a vessel is not anchored, or secured to the shore, or aground.

Where does it apply? At sea and on connected navigable waters.

Also known as: Variation

What is it? The error between Magnetic North and True North.

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V

Also known as: Vector

What is it? Vectors can be displayed showing the heading speed through the water or speed over ground and course over ground. Vectors can be set for specific time frames or distances or be set to infinite.

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Also known as: Vector chart

What is it? A style of digital chart made up of a database with information grouped within layers. The chart can be adjusted to change colour palette and safety contours and hide non-relevant information. Use of vector charts requires and understand of the setting in use on the charts. Vectors can be displayed showing the heading speed through the water or speed over ground and course over ground. Vectors can be set for specific time frames or distances or be set to infinite.

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Also known as: Vertical datum

What is it? Vertical datums are used to measure land elevations and water depths.

Where does it apply? Datums vary depending on where you are.

Also known as: VHF

What is it? An important piece of safety equipment in which you need an operator’s certificate to use one. The Short Range Certificate (SRC) is the minimum qualification required by law to control the operation of VHF and VHF Digital Selective Calling (DSC) equipment on any British flagged vessel fitted with a radio either fixed or hand held.

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W

Also known as: Water track

What is it? The direction the vessel is moving through the water, allowing for leeway.

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Also known as: Waypoint (WPT)

What is it? A significant point within a route. It is typically a point where a decision or action is required, such as alteration or course or speed. When used within an electronic navigation system, a waypoint can be set up to alert the navigator in advance of arriving at the waypoint. A meaning, name, and detailed notes may be stored to clarify the action or decision that is needed, ensuring all watchkeepers execute the correct navigational plan.

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Also known as: Windward

What is it? Towards the wind, the side facing the wind.

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"The windward side of the boat"

"Windward shore"

"We need to steer to windward"

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