Glossary

The leg you are currently following; its end waypoint is the active waypoint.

From the lesson Electronic Nav · Waypoints, Routes and XTE

Fog formed when warm moist air flows over a colder sea surface and is chilled to its dew point. The true sea fog.

From the lesson Weather · Fog and Poor Visibility

The tendency of a cold casualty to get worse just after rescue, as chilled blood recirculates and blood pressure falls. The reason cold casualties are recovered horizontally and handled gently.

From the lesson Safety · Crew Health and First Aid Basics

A vast body of air with fairly uniform temperature and humidity, shaped by the surface it came from — polar, tropical, maritime or continental.

From the lesson Weather · Fronts and Depressions

Automatic Identification System — VHF broadcasts of vessel identity, position, course and speed, displayed as targets on a plotter.

From the lesson Electronic Nav · AIS and Radar Basics

Visible over the full 360° — anchor lights and the special identity lights.

From the lesson ColRegs · Navigation Lights and Day Shapes

The middle of the boat, along its length or on its centreline.

From the lesson Seamanship · Parts of a Yacht

The wind measured aboard a moving boat — true wind combined with the wind created by your own motion.

From the lesson Electronic Nav · Instruments and the Modern Nav Station

The first stage of passage planning: gathering and weighing all relevant information about the route, weather, tides, boat and crew before committing to a plan.

From the lesson Passage Planning · Appraisal: Gathering Information

The weight of the air pressing down on the surface, measured in hectopascals (hPa). One hectopascal equals one millibar.

From the lesson Weather · Air Pressure and Weather Systems

The wind direction shifting anticlockwise, e.g. west to south-west to south. A backing, freshening wind often signals an approaching depression.

From the lesson Weather · Fronts and Depressions

The wire from the masthead to the stern, stopping the mast falling forwards.

From the lesson Seamanship · Sails and Rigging

The minimum speed at which the boat still answers her helm.

From the lesson ColRegs · Conduct in Restricted Visibility

An instrument that measures atmospheric pressure. On a boat, its trend over time matters far more than any single reading.

From the lesson Weather · Air Pressure and Weather Systems

The widest part of the boat. Something out to the side is abeam.

From the lesson Seamanship · Parts of a Yacht

The direction of an object from your boat, in degrees. Compass bearings must be converted to true before plotting.

From the lesson Position Fixing · Position Lines and Visual Fixes

Zig-zagging upwind, close-hauled on one tack and then the other, because no boat sails straight into the wind.

From the lesson Seamanship · Boat Handling Under Power and Sail

A slack loop formed without crossing the line over itself.

From the lesson Seamanship · Ropework and Knots

The very last inboard end of a line.

From the lesson Seamanship · Ropework and Knots

Removing air from the fuel lines after running dry or changing a filter — air in the lines stops a diesel dead. Many modern engines self-bleed.

From the lesson Seamanship · Engines and Boat Systems

A rectangular protractor with a rotating compass dial and a grid. You align the grid with the chart's meridians and read courses directly — no compass rose needed.

From the lesson Chartwork · Plotting Tools and Techniques

Bearing to waypoint — the direction from the boat straight to the active waypoint, right now.

From the lesson Electronic Nav · Waypoints, Routes and XTE

A foam vest giving modest permanent buoyancy (around 50 Newtons). It supports a conscious swimmer but will not turn an unconscious casualty face-up.

From the lesson Safety · Personal Safety Equipment

One tenth of a nautical mile, about 185 m. Handy for short distances in pilotage.

From the lesson Chartwork · Distance, Speed and Depth

A power-driven vessel severely restricted by the depth and width of available water relative to her draught.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

The international distress, safety and calling channel (156.8 MHz). All vessels should monitor it at sea; working conversations move off it to other channels.

From the lesson Safety · VHF Radio and Distress Procedures

The full description of a light: its rhythm, colour and period, e.g. Fl(2) R 6s — everything you need to identify it at night.

From the lesson Pilotage · Lights and Their Characteristics

The reference level for depths and tidal heights on a chart. On modern UK charts it is set at LAT, so the tide almost never falls below it.

From the lesson Tides · Tide Tables and Heights of Tide

The depth of the seabed below chart datum, printed on the chart in metres and decimetres.

From the lesson Tides · Tide Tables and Heights of Tide

The safe gap under a bridge or cable, measured on modern UK charts above highest astronomical tide (HAT); older charts used MHWS. Check the chart notes.

From the lesson Tides · Tide Tables and Heights of Tide

The deliberate safety margin you leave between your track and a danger — distance off a headland, or depth beneath the keel.

From the lesson Passage Planning · Planning the Route

A pre-drawn bearing of a fixed object that separates safe water from danger: while the object bears less than (or more than) the stated value, you are on the safe side.

From the lesson Position Fixing · Transits, Clearing Bearings and Soundings

A T-shaped fitting to which lines are secured, on deck and on pontoons.

From the lesson Seamanship · Parts of a Yacht

An approach so close that collision becomes a real possibility. In fog, think in miles, not boat-lengths — big ships need sea room to react.

From the lesson ColRegs · Conduct in Restricted Visibility

Course over the ground, from GNSS — the direction you are actually tracking, which may differ markedly from where the bow points.

From the lesson Electronic Nav · Instruments and the Modern Nav Station

Course over ground and speed over ground, as measured by GNSS — your ground track, tide and leeway included.

From the lesson Position Fixing · Fixing in Practice

The leading edge of advancing cold air. Cold air undercuts the warm air abruptly, giving a narrow, violent band of heavy rain and squalls.

From the lesson Weather · Fronts and Depressions

The body's violent first response to sudden cold immersion: gasping, hyperventilation and a racing heart, lasting around a minute. The main drowning risk of falling overboard.

From the lesson Safety · Crew Health and First Aid Basics

The International Regulations for Preventing Collisions at Sea — the rules of the road for all vessels.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

Direction measured from your compass north — what your steering compass actually reads.

From the lesson Chartwork · Direction: True, Magnetic and Compass

The scale at which a chart's data was compiled for use. Zooming beyond it shows the same data larger, never more data.

From the lesson Electronic Nav · Chart Plotters and Electronic Charts

A family of satellites operated as one system: GPS (USA), Galileo (Europe), GLONASS (Russia), BeiDou (China). Modern receivers track several at once.

From the lesson Electronic Nav · GNSS Fundamentals

The international satellite system that detects 406 MHz distress beacons anywhere on Earth and passes the alert, with position, to rescue authorities.

From the lesson Safety · The Boat's Safety Equipment

The direction of the ground track, as a GPS reports it. COG is measured from where you were to where you are — it looks backwards, not forwards.

From the lesson Course to Steer · Ground Track vs Water Track

The compass direction the helm has actually been steering, converted to true degrees for plotting on the chart.

From the lesson Position Fixing · Dead Reckoning

Closest point of approach — the minimum distance a target will pass from you if both vessels hold their current course and speed.

From the lesson Electronic Nav · AIS and Radar Basics

Verifying a position by an independent method — a bearing, a transit, a depth — so one hidden error cannot mislead you.

From the lesson Position Fixing · Fixing in Practice

How far the boat is displaced sideways from the straight line between two waypoints. The GPS displays it; the tide causes most of it.

From the lesson Passage Planning · Planning the Route

Wind term meaning the wind direction will change considerably as a depression centre passes through the area — expect the full rotation, not one steady direction.

From the lesson Weather · Getting and Reading Forecasts

A tall floating pole with a flag, weighted to stand upright, thrown to mark the position of a person in the water. Visible far beyond a swimmer's head.

From the lesson Safety · Man Overboard

Estimating your present position by applying the course steered and the distance run through the water to your last known position. It ignores tide and wind drift.

From the lesson Position Fixing · Dead Reckoning

A pre-planned place or time at which you deliberately reassess the passage and choose to continue, divert or turn back.

From the lesson Passage Planning · Execution and Monitoring

The actual depth right now: charted depth plus height of tide (or height of tide minus drying height over a drying patch).

From the lesson Tides · Tide Tables and Heights of Tide

The angle between magnetic north and your compass north, named E or W, varying with heading. Found on the deviation card.

From the lesson Chartwork · Direction: True, Magnetic and Compass

The temperature to which air must be cooled for its water vapour to start condensing. Air at its dew point is saturated.

From the lesson Weather · Fog and Poor Visibility

Microbial growth at the diesel-water interface in the tank; its black sludge blocks filters. Prevention: full tanks, clean fuel.

From the lesson Seamanship · Engines and Boat Systems

The reference direction that decides which side is which — generally the direction you travel when approaching a harbour, river or estuary from seaward.

From the lesson Pilotage · IALA Buoyage (Region A)

A pattern with only one high and one low water per day, found in some other parts of the world.

From the lesson Tides · How Tides Work

A two-pointed measuring instrument for taking distances to and from the latitude scale. Single-handed (bow) dividers can be worked with one hand at sea.

From the lesson Chartwork · Plotting Tools and Techniques

The distance the stream carries the water in a given time, in nautical miles. A 2-knot stream for one hour gives a drift of 2 M.

From the lesson Position Fixing · The Estimated Position

How far a bank or rock rises above chart datum. Shown underlined on the chart. It is covered only when the height of tide exceeds it.

From the lesson Tides · Tide Tables and Heights of Tide

A digital signalling system built into modern VHF sets that can send an automatic, addressed alert — including a distress alert with your MMSI and position — at the push of a button.

From the lesson Safety · VHF Radio and Distress Procedures

Distance to waypoint — how far the boat is from the active waypoint, in a straight line.

From the lesson Electronic Nav · Waypoints, Routes and XTE

An interval of darkness within the rhythm of a light — the dark part of the cycle.

From the lesson Pilotage · Lights and Their Characteristics

Blue and yellow vertical stripes, alternating blue and yellow light, yellow upright cross topmark. Laid over a new, still-uncharted wreck until permanent marks are established.

From the lesson Pilotage · IALA Buoyage (Region A)

Electronic Navigational Chart — an official vector chart issued under national hydrographic office authority.

From the lesson Electronic Nav · Chart Plotters and Electronic Charts

Emergency Position Indicating Radio Beacon: a buoyant beacon registered to the vessel that transmits a distress signal on 406 MHz to the worldwide Cospas-Sarsat satellite system.

From the lesson Safety · The Boat's Safety Equipment

A pre-planned safe exit from any point of the pilotage — where you will go and how, if the entrance is blocked, the plan fails, or conditions turn bad.

From the lesson Pilotage · Making a Pilotage Plan

A DR improved by allowing for leeway and tidal stream. Plotted as a dot inside a small triangle, with the time.

From the lesson Position Fixing · The Estimated Position

Forecast weather term meaning no significant precipitation.

From the lesson Weather · Getting and Reading Forecasts

Guides a mooring line over the deck edge at the correct angle, preventing chafe.

From the lesson Seamanship · Parts of a Yacht

The distance of open water the wind has blown across. Long fetch allows big waves to build; short fetch keeps them small.

From the lesson Weather · Wind, Sea Breezes and Sea State

The mechanism on an inflatable lifejacket that punctures the gas cylinder. Automatic heads fire when immersed; manual heads fire only when you pull the toggle.

From the lesson Safety · Personal Safety Equipment

A position established by direct observation — typically the crossing of two or more position lines taken at the same time. Plotted as a dot in a circle with the time.

From the lesson Position Fixing · Position Lines and Visual Fixes

Visibility below 1,000 metres caused by water droplets suspended in the air.

From the lesson Weather · Fog and Poor Visibility

The wire from the mast to the bow, stopping the mast falling backwards. The headsail hoists on or around it.

From the lesson Seamanship · Sails and Rigging

Towards the bow (forward) and towards the stern (aft).

From the lesson Seamanship · Parts of a Yacht

The boundary between two air masses. Drawn on charts as a line: red semicircles for a warm front, blue triangles for a cold front.

From the lesson Weather · Fronts and Depressions

Rolls a furling headsail away around the forestay, like a roller blind.

From the lesson Seamanship · Sails and Rigging

Mean wind 34-40 knots. A gale warning covers mean F8+ or gusts of 43 knots or more.

From the lesson Weather · Getting and Reading Forecasts

The opening summary of where the highs, lows and fronts are, their central pressures, and where they are expected to move.

From the lesson Weather · Getting and Reading Forecasts

Must keep out of the way of the other, taking early and substantial action to keep well clear.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

Global Navigation Satellite System — the family name for satellite positioning: GPS (USA), Galileo (EU), GLONASS (Russia), BeiDou (China).

From the lesson Position Fixing · Fixing in Practice

The hinged fitting joining the boom to the mast, letting the boom swing from side to side.

From the lesson Seamanship · Sails and Rigging

The large-scale wind driven by the pressure pattern on the synoptic chart, before local coastal effects are added.

From the lesson Weather · Wind, Sea Breezes and Sea State

The direction the boat actually moves over the seabed: water track combined with tidal stream. Drawn with two arrowheads.

From the lesson Position Fixing · The Estimated Position

Wires around the deck edge, supported by vertical posts (stanchions) and anchored at the pulpit and pushpit, to help keep crew aboard.

From the lesson Seamanship · Parts of a Yacht

A brief surge of wind lasting seconds, caused by faster air from above mixing down to the surface. Gusts typically run 30 to 50 percent above the mean wind speed.

From the lesson Weather · Wind, Sea Breezes and Sea State

A small portable compass with a sighting notch or prism, used to measure the bearing of distant objects. It reads in magnetic degrees.

From the lesson Position Fixing · Position Lines and Visual Fixes

Pointing straight into the wind, sails flapping — used deliberately when hoisting sails or picking up a mooring.

From the lesson Seamanship · Boat Handling Under Power and Sail

The direction the boat is pointing at this moment — what the steering compass reads. It says nothing about where you are actually going.

From the lesson Course to Steer · Ground Track vs Water Track

Metres to add or subtract from the standard port's HW or LW height, quoted separately for springs (MHWS/MLWS) and neaps (MHWN/MLWN).

From the lesson Tides · Secondary Ports

How far the sea surface currently stands above chart datum. This is what tide tables and tidal curves give you.

From the lesson Tides · Tide Tables and Heights of Tide

The highest level the tide reaches in one cycle, and the time at which it happens.

From the lesson Tides · How Tides Work

A U-shaped buoy mounted on the pushpit that a casualty can get inside without help, often fitted with a light and drogue.

From the lesson Safety · Man Overboard

A dangerous fall in core body temperature, from cold water or simply from long, cold, wet hours on deck. It creeps up on watchkeepers as surely as on swimmers.

From the lesson Safety · Crew Health and First Aid Basics

To force another vessel to alter course or speed to avoid you. Not impeding means arranging your passage so early that the question never arises.

From the lesson ColRegs · Narrow Channels and Traffic Schemes

A qualified professional who lives aboard with you, teaches the syllabus, keeps everyone safe, and confirms you reach the standard by the end of the week.

From the lesson Practical Prep · What to Expect on the Practical Course

How many hours before or after high water a given moment is — the way the curve measures time. Written like HW−2 or HW+3.

From the lesson Tides · Tidal Curves

A line on a weather map joining places with equal pressure, usually drawn every 4 hPa. Think of them as contour lines for the atmosphere.

From the lesson Weather · Air Pressure and Weather Systems

Black with red band(s), two black spheres topmark, white Fl(2) light — two flashes echoing the two spheres. A small danger with navigable water around it: pass well clear on any side, because the danger is directly beneath.

From the lesson Pilotage · IALA Buoyage (Region A)

A webbing strap or wire running along the deck from bow to stern, to which you clip your tether so you can walk the length of the boat without unclipping.

From the lesson Safety · Personal Safety Equipment

Strong webbing or wire lines along the deck that crew clip their safety tethers to when moving forward.

From the lesson Seamanship · Parts of a Yacht

One nautical mile per hour. The standard unit of speed at sea — never say knots per hour.

From the lesson Chartwork · Distance, Speed and Depth

A buoy or beacon marking the side of a channel. In Region A: red can to port, green cone to starboard, when travelling with the direction of buoyage.

From the lesson Pilotage · IALA Buoyage (Region A)

Angular distance north or south of the equator, 0° to 90°, written with N or S.

From the lesson Chartwork · Latitude, Longitude and Position

A transit deliberately built to mark a safe approach: keep the front and rear marks in line and you stay on the charted leading line into the harbour.

From the lesson Position Fixing · Transits, Clearing Bearings and Soundings

The direction the wind is blowing towards; downwind. Pronounced loo-ard by sailors. Leeway always pushes the boat to leeward.

From the lesson Course to Steer · Leeway

The angle between the boat's heading and her track through the water, caused by the wind pushing her bodily downwind.

From the lesson Position Fixing · The Estimated Position

An inflatable (or solid) jacket with enough buoyancy, correctly distributed, to turn most unconscious wearers face-up and support the airway clear of the water.

From the lesson Safety · Personal Safety Equipment

The instrument that measures speed and distance travelled through the water — not over the seabed.

From the lesson Position Fixing · Dead Reckoning

Angular distance east or west of the Greenwich meridian, 0° to 180°, written with E or W.

From the lesson Chartwork · Latitude, Longitude and Position

The lowest level the tide reaches in one cycle, and the time at which it happens.

From the lesson Tides · How Tides Work

The lowest sea level that can be predicted from astronomy alone, ignoring weather effects.

From the lesson Tides · Tide Tables and Heights of Tide

Direction measured from magnetic north — what a perfect compass free of the boat would read.

From the lesson Chartwork · Direction: True, Magnetic and Compass

White, over her fore-and-aft centreline — the badge of engine propulsion. Despite the name it need not be at the top of the mast.

From the lesson ColRegs · Navigation Lights and Day Shapes

A long-term average sea level. Averages of HW and LW at springs and neaps give the standard levels MHWS, MHWN, MLWN and MLWS, which you will meet in the next lesson.

From the lesson Tides · How Tides Work

The average range at springs and at neaps, printed next to the curve. Compare the day's actual range with these to choose between the solid and dashed lines.

From the lesson Tides · Tidal Curves

A line of constant longitude, running from pole to pole.

From the lesson Chartwork · Latitude, Longitude and Position

One sixtieth of a degree. Written with a prime mark, and subdivided into decimals in modern practice.

From the lesson Chartwork · Latitude, Longitude and Position

Thinner droplet haze with visibility above 1,000 metres. Often the stage just before or after fog.

From the lesson Weather · Fog and Poor Visibility

Maritime Mobile Service Identity — the unique nine-digit number identifying a vessel's radio installation, used by AIS and DSC.

From the lesson Electronic Nav · AIS and Radar Basics

A function on GPS sets and plotters that instantly stores the current position and displays bearing and distance back to it.

From the lesson Safety · Man Overboard

A confined stretch of navigable water, often buoyed or dredged, where larger vessels have little room to deviate. No width in metres — judge by whether traffic is confined.

From the lesson ColRegs · Narrow Channels and Traffic Schemes

1,852 metres; one minute of latitude. The standard unit of distance at sea.

From the lesson Chartwork · Distance, Speed and Depth

The tides with the smallest range, occurring shortly after the Moon's quarters, in between springs.

From the lesson Tides · How Tides Work

The unit used to rate buoyancy. Roughly 10 Newtons supports 1 kilogram in water; a 150N lifejacket gives about 15 kg of lift.

From the lesson Safety · Personal Safety Equipment

Hours underway between sunset and sunrise, logged separately because advanced courses require a minimum of them.

From the lesson Practical Prep · After the Course: Building Experience

Unable to manoeuvre as the rules require through some exceptional circumstance — engine or steering failure.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

Formed when the faster cold front catches up with the warm front and lifts the warm air off the surface, merging the weather of both fronts.

From the lesson Weather · Fronts and Depressions

Tensions the foot of the mainsail along the boom — tighter for a flatter sail.

From the lesson Seamanship · Sails and Rigging

Rough, breaking water caused by a fast stream running over an uneven bottom or against the wind. Marked on charts with a wavy symbol and best avoided.

From the lesson Tides · Tidal Streams

A line of constant latitude, running east–west.

From the lesson Chartwork · Latitude, Longitude and Position

Two linked straight edges that walk across the chart while staying parallel, used to carry a direction to or from the printed compass rose.

From the lesson Chartwork · Plotting Tools and Techniques

The output of planning: a route with courses, distances and timings, plus tidal calculations, dangers, ports of refuge and contingencies.

From the lesson Passage Planning · Appraisal: Gathering Information

The time for one complete cycle of the rhythm, measured from the start of one sequence to the start of the next, including the dark interval.

From the lesson Pilotage · Lights and Their Characteristics

A pre-prepared summary — usually a sketch plus notes — of courses, distances, marks, lights, depths, tidal data and hazards for entering or leaving a harbour.

From the lesson Pilotage · Making a Pilotage Plan

The pre-considered alternative — a port of refuge, a delayed start, an anchorage to wait out a foul tide — ready before it is needed.

From the lesson Passage Planning · Execution and Monitoring

Personal Locator Beacon: a pocket-sized 406 MHz beacon registered to a person, carried in the lifejacket. It must be activated manually and held clear of the water.

From the lesson Safety · The Boat's Safety Equipment

The boat's left-hand side when facing the bow. Marked by the colour red.

From the lesson Seamanship · Parts of a Yacht

Wind over the port side; boom carried out to starboard.

From the lesson ColRegs · Give-Way Rules Between Vessels

Any line on the chart on which you know your vessel must lie. A compass bearing of a charted object gives one; so do a transit, a depth contour or a radar range.

From the lesson Position Fixing · Position Lines and Visual Fixes

How quickly pressure changes with distance. A steep gradient (isobars close together) means strong wind.

From the lesson Weather · Air Pressure and Weather Systems

A sound signal of four to six seconds on the whistle or horn.

From the lesson ColRegs · Narrow Channels and Traffic Schemes

A passage meeting specific criteria (distance, duration, role) that counts toward the entry requirements of an advanced course or certificate.

From the lesson Practical Prep · After the Course: Building Experience

Fog formed over land on clear calm nights as the ground radiates its heat away and chills the air above it.

From the lesson Weather · Fog and Poor Visibility

Her work prevents free manoeuvring: dredging, laying cable, servicing buoys, minesweeping.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

The height difference between a high water and the following (or preceding) low water. Range = HW height minus LW height.

From the lesson Tides · How Tides Work

The speed of the stream, in knots.

From the lesson Tides · Tidal Streams

Pull down and secure part of the mainsail to reduce its area — taking in a reef.

From the lesson Seamanship · Sails and Rigging

The straight line on the chart from where you are (A) to where you want to be (B). This is the result you are trying to achieve.

From the lesson Course to Steer · Constructing a Course to Steer

Any condition — fog, mist, falling snow, heavy rain or similar — in which visibility is restricted.

From the lesson ColRegs · Conduct in Restricted Visibility

Raster Navigational Chart — an official scanned image of a paper chart.

From the lesson Electronic Nav · Chart Plotters and Electronic Charts

An ordered sequence of waypoints; the plotter guides you along each leg in turn.

From the lesson Electronic Nav · Waypoints, Routes and XTE

Red and white vertical stripes, single red sphere topmark, white Iso, Oc, LFl 10s or Mo(A) light. Navigable water all round — often the landfall buoy where a buoyed channel begins.

From the lesson Pilotage · IALA Buoyage (Region A)

Strong webbing worn around the chest with a metal D-ring for attaching a tether. On most modern lifejackets the harness is built in.

From the lesson Safety · Personal Safety Equipment

Search And Rescue Transponder: a device that makes you conspicuous on rescuers' radar or AIS screens at close range during the final search.

From the lesson Safety · The Boat's Safety Equipment

Scale minimum — an attribute on vector chart objects that hides them when you zoom out too far, to reduce clutter. Some plotter settings can also thin out detail in ways you must check.

From the lesson Electronic Nav · Chart Plotters and Electronic Charts

The ratio of rode paid out to the maximum depth of water.

From the lesson Seamanship · Anchoring and Mooring

A large named block of sea used by the shipping forecast. Forecasts read the areas in a fixed geographical order.

From the lesson Weather · Getting and Reading Forecasts

A port whose tides are published only as time and height differences to be applied to a named standard port.

From the lesson Tides · Secondary Ports

A tidal pattern with two high waters and two low waters per day — the normal pattern around the British Isles.

From the lesson Tides · How Tides Work

The direction towards which a tidal stream flows, in true degrees. A stream setting 180° carries you south.

From the lesson Position Fixing · The Estimated Position

Mean wind 41-47 knots, or gusts 52 knots or more.

From the lesson Weather · Getting and Reading Forecasts

A short first sail to check the boat, introduce the crew to the deck layout, and let the instructor gauge everyone's starting level.

From the lesson Practical Prep · What to Expect on the Practical Course

The wires supporting the mast from each side — cap shrouds to the masthead, lower shrouds to the middle.

From the lesson Seamanship · Sails and Rigging

Green on her starboard side, red on her port side, each screened so it cannot be seen from the other side.

From the lesson ColRegs · Navigation Lights and Day Shapes

The short period, usually near the turn of the stream, when the water is barely moving.

From the lesson Tides · Tidal Streams

A short stretchy nylon line from the chain to a cleat — it absorbs shocks and takes the load off the windlass.

From the lesson Seamanship · Anchoring and Mooring

A 2B pencil draws lines you can actually remove. Chartwork in pen, or hard pencil, ruins charts.

From the lesson Chartwork · Plotting Tools and Techniques

Speed over the ground, from GNSS — your true progress across the chart, including every effect of tide and leeway.

From the lesson Electronic Nav · Instruments and the Modern Nav Station

The part of the international Safety of Life at Sea convention that covers safe navigation, including the duty on every vessel — pleasure craft included — to plan its voyage before going to sea.

From the lesson Passage Planning · Appraisal: Gathering Information

Yellow, optional yellow X topmark, yellow light. Marks a feature such as a racing mark, outfall or exercise area rather than a navigational danger — the chart says which.

From the lesson Pilotage · IALA Buoyage (Region A)

How fast you are moving over the seabed. With a fair (favourable) tide, SOG is higher than boat speed; against a foul tide, it is lower.

From the lesson Course to Steer · Ground Track vs Water Track

The crew member whose single task is to keep eyes on the casualty and point, never looking away — not even to help with sails.

From the lesson Safety · Man Overboard

Struts partway up the mast that push the cap shrouds outwards, improving their supporting angle.

From the lesson Seamanship · Sails and Rigging

The tides with the largest range, occurring shortly after new and full Moon, roughly every two weeks.

From the lesson Tides · How Tides Work

A sudden, sustained increase in wind lasting minutes, usually arriving with a shower cloud or a front, and often with a sharp shift in direction.

From the lesson Weather · Wind, Sea Breezes and Sea State

A period around high or low water when the level barely changes. Some ports have pronounced stands, which is exactly what their own curve captures.

From the lesson Tides · Tidal Curves

Must hold her course and speed, so the give-way vessel can plan around something predictable.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

A port with full daily tide tables printed in the almanac — times and heights of every HW and LW, plus its own tidal curve.

From the lesson Tides · Secondary Ports

The rest of the line — under load or leading away from the knot.

From the lesson Seamanship · Ropework and Knots

The boat's right-hand side when facing the bow. Marked by the colour green.

From the lesson Seamanship · Parts of a Yacht

Wind over the starboard side; boom carried out to port.

From the lesson ColRegs · Give-Way Rules Between Vessels

White, at her stern, showing aft over both quarters.

From the lesson ColRegs · Navigation Lights and Day Shapes

A dedicated attachment point, usually in or near the cockpit, engineered to take the shock load of a falling body.

From the lesson Safety · Personal Safety Equipment

Inshore waters warning for expected winds of Force 6 or more — a signal for small craft to think hard about staying in port.

From the lesson Weather · Getting and Reading Forecasts

Speed through the water, from the log. Used with the compass heading for traditional chartwork (EP and course to steer).

From the lesson Electronic Nav · Instruments and the Modern Nav Station

Any other vessel or object being tracked, whether by AIS or radar.

From the lesson Electronic Nav · AIS and Radar Basics

Time to closest point of approach — how many minutes until that minimum distance occurs.

From the lesson Electronic Nav · AIS and Radar Basics

A strong line, usually 1–2 metres of webbing with safety hooks at each end, connecting your harness to the boat.

From the lesson Safety · Personal Safety Equipment

A graph showing how the height of tide at a port typically changes through the hours before and after high water.

From the lesson Tides · Tidal Curves

The horizontal movement of the water caused by the tide, tabulated on charts and in tidal stream atlases.

From the lesson Position Fixing · The Estimated Position

A place — typically a headland, race or narrow channel — where the stream runs so hard that you can only pass it in practice when the stream is favourable or slack.

From the lesson Tides · Tidal Streams

A line representing one hour of tidal stream: drawn in the direction of the set, with a length equal to the drift (rate x 1 hour).

From the lesson Course to Steer · Constructing a Course to Steer

Minutes to add to (or subtract from) the standard port's HW or LW time to get the secondary port's time. Written like +0030 or −0015.

From the lesson Tides · Secondary Ports

To secure a line to a cleat or other fitting.

From the lesson Seamanship · Ropework and Knots

A distinctive shape fitted to the top of a buoy or beacon, repeating the mark's message in a form you can read at a distance or in silhouette.

From the lesson Pilotage · IALA Buoyage (Region A)

Holds the boom up when the mainsail is lowered.

From the lesson Seamanship · Sails and Rigging

The sides of the hull between the waterline and the deck — the part you protect with fenders.

From the lesson Seamanship · Parts of a Yacht

Yellow, over the same arc as the sternlight and shown above it by a vessel towing.

From the lesson ColRegs · Navigation Lights and Day Shapes

Two fixed, charted objects seen exactly in line. The observer must lie on the extension of the line through both — an instant position line requiring no instrument.

From the lesson Position Fixing · Transits, Clearing Bearings and Soundings

The flat surface across the stern; on many modern yachts it folds down as a bathing platform.

From the lesson Seamanship · Parts of a Yacht

Fixing a position from measured distances to known points, rather than from bearings.

From the lesson Electronic Nav · GNSS Fundamentals

A light line from the anchor's crown to a small buoy, used to pull a fouled anchor out backwards.

From the lesson Seamanship · Anchoring and Mooring

Direction measured from true (geographic) north — the reference used on charts.

From the lesson Chartwork · Direction: True, Magnetic and Compass

The wind over the sea surface itself, as an anchored observer would feel it. Instruments calculate it from apparent wind and boat speed.

From the lesson Electronic Nav · Instruments and the Modern Nav Station

Not at anchor, not made fast to the shore, and not aground. A boat drifting with her engine off is still underway.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

The angle between true and magnetic north at your location, named E or W. Found on the chart compass rose.

From the lesson Chartwork · Direction: True, Magnetic and Compass

The wind direction shifting clockwise, e.g. south to south-west to west. Each front of a passing depression brings a veer (northern hemisphere).

From the lesson Weather · Fronts and Depressions

Fishing with nets, lines or trawls that restrict manoeuvrability — not a yacht trailing a mackerel line.

From the lesson ColRegs · Foundations: Lookout, Speed and Risk

The marine radio band. Range is roughly line-of-sight: typically up to about 20 miles to a coast station from a masthead aerial, and perhaps 5 miles between handhelds.

From the lesson Safety · VHF Radio and Distress Procedures

Provisioning the boat with food and drink for the passage — pronounced vittling. Good victualling favours food that can be eaten one-handed in a seaway.

From the lesson Passage Planning · Preparing Boat and Crew

The leading edge of advancing warm air. The warm air slides gently up over the cold air ahead, giving a long, slow build-up of cloud and steady rain.

From the lesson Weather · Fronts and Depressions

The wedge of warm, moist air between the warm front and the cold front of a depression — typically mild, murky and drizzly at sea.

From the lesson Weather · Fronts and Depressions

A rota dividing the crew into shifts so the boat is always properly crewed while everyone gets planned rest.

From the lesson Passage Planning · Preparing Boat and Crew

The direction the boat actually moves through the water: course steered adjusted for leeway. Drawn with one arrowhead.

From the lesson Position Fixing · The Estimated Position

A line representing one hour of the boat moving through the water: its length is your boat speed, and its direction is the answer — the course to steer.

From the lesson Course to Steer · Constructing a Course to Steer

A stored position a navigation system can steer towards — only as good as the hand that entered it.

From the lesson Position Fixing · Fixing in Practice

The worldwide reference model of the Earth used by GNSS. Modern charts are drawn to WGS84, so plotter positions and chart positions agree.

From the lesson Electronic Nav · GNSS Fundamentals

A geared drum that gives you the mechanical power to haul lines under load.

From the lesson Seamanship · Parts of a Yacht

The winch at the bow, manual or electric, that hauls the anchor and chain back aboard.

From the lesson Seamanship · Anchoring and Mooring

The direction the wind is coming from; upwind. To go to windward is to move towards the wind.

From the lesson Course to Steer · Leeway

The end of the line you are tying with.

From the lesson Seamanship · Ropework and Knots

Cross-track error — how far the boat is displaced sideways from the planned track line, usually with an arrow or L/R marker showing which side.

From the lesson Electronic Nav · Waypoints, Routes and XTE