RYA Day Skipper Theory cheat sheet

Latitude is measured north or south of the equator, 0° to 90°; longitude is measured east or west of Greenwich, 0° to 180°.

1 minute of latitude = 1 nautical mile (1852 m). Measure distances on the latitude scale level with the position, never on the longitude scale.

1 minute of longitude = 1 NM × cos(latitude), so the longitude scale shrinks towards the poles.

Chart datum is normally Lowest Astronomical Tide; soundings and drying heights are referenced to it, and charted heights of objects to Mean High Water Springs.

A position fix from two bearings is weakest when the angle of cut is small; aim for a cut near 90°, and 60–120° is acceptable.

Three-point fix: a cocked hat under about 5 mm on the chart is treated as a fix; the centre of the triangle is the position.

A running fix: plot the first position, lay off the course and distance run (from log or speed × time) to transfer the position line, then cross it with a second position line.

Course to steer to counteract a current: lay off the tidal stream vector from the start, then a line from the end of the stream to the destination; its direction is the course to steer, and its length is the distance through the water.

Set is the direction the tidal stream flows towards, expressed in degrees true; rate is its speed in knots.

Spring tides occur near new and full moon (about 1–2 days later); neap tides near the first and third quarters.

Rule of Twelfths over a 6-hour rise or fall: 1/12, 2/12, 3/12, 3/12, 2/12, 1/12 each hour.

Height of tide at a time between HW and LW = HW height − (range × accumulated twelfths); add when rising from LW, subtract when falling from HW.

Standard port data give HW/LW times and heights; secondary port differences are applied as time differences (minutes) and height differences (metres) to the standard port predictions.

Range = HW height − LW height. Mean range = MHWS − MLWS; spring range is larger than neap range.

Chart datum is approximately LAT, so charted depths are the least depth expected; height of tide must be added to charted depth to get actual depth.

Under-keel clearance = charted depth + height of tide − draught; allow for squat and for the height of tide at the time of the passage, not at HW.

Duration of rise or fall is the interval between successive HW and LW; use it to place the time within the twelfths table.

Rule of thumb: HW at a standard port is delayed by roughly 50 minutes each day (lunar day ≈ 24 h 50 min).

CTS = course over ground ± leeway ± tidal set correction; the course steered is through the water, the track made good is over the ground.

Speed made good = distance over the ground ÷ elapsed time; compare with boat speed to detect favourable or adverse stream.

Dead reckoning uses course steered and distance run (log) with no external fix; estimated position adds estimated leeway and tidal stream.

A passage plan has four stages: appraisal, planning, execution, and monitoring; it covers departure, the passage, and arrival.

Pilotage plan: identify landfall, transits, clearing bearings, and a safe track with contingency anchorages; note minimum depths, hazards, and abort points.

A transit (two objects in line) gives a position line along the line of the objects; a clearing bearing keeps the vessel on the safe side of a hazard.

A sector light shows different colours over different arcs; the safe sector is the white one, and it must be identified from the chart or almanac, not assumed.

IALA Region A (Europe, most of the world): port-hand marks are red cans, starboard-hand marks are green cones; Region B (Americas, Japan, Korea, Philippines) is reversed.

Cardinal marks: two cones indicate the safe quadrant - north both up, south both down, east base-to-base, west point-to-point; the light flashes match the clock face (N 1, E 3, S 6, W 9).

COLREGS Rule 5: a proper lookout by sight and hearing, and by all available means, must be maintained at all times.

Rule 6 safe speed: consider visibility, traffic density, manoeuvrability, background light, sea state, and stopping distance.

Rule 7 risk of collision: if in doubt, assume it exists; a steady bearing and decreasing range indicates risk.

Rule 13 overtaking: the overtaking vessel keeps clear; the overtaken vessel holds course and speed.

Rule 14 head-on: both alter course to starboard and pass port-to-port.

Rule 15 crossing: the vessel with the other on her starboard side gives way; the stand-on vessel keeps course and speed but may act if collision cannot be avoided by the give-way vessel alone.

Rule 12 sailing vessels: windward keeps clear of leeward; if either is on port tack, the port-tack vessel keeps clear; if in doubt, the vessel upwind keeps clear.

Rule 18 power-driven vessels give way to sailing vessels, vessels not under command, restricted in ability to manoeuvre, and fishing vessels; a vessel constrained by draught is not automatically a stand-on vessel.

Rule 19 restricted visibility: reduce speed to a safe speed, sound fog signals, and take avoiding action as soon as risk is detected; the steering and sailing rules (12–18) do not apply.

Manoeuvring signals: one short blast = altering to starboard, two short = port, three short = operating astern propulsion; at least five short and rapid blasts = doubt or danger.

Fog signals: power-driven vessel making way = one prolonged blast every 2 minutes; stopped = two prolonged blasts with a 2-second interval every 2 minutes; sailing vessel = one prolonged plus two short every 2 minutes.

Distress signals include MAYDAY on VHF Ch 16, red parachute flares, orange smoke, and DSC distress alert; a MAYDAY RELAY is used when another vessel's distress is relayed.

Lifejackets must be worn on deck in poor visibility, at night, in strong winds, and when the skipper judges it necessary; a danbuoy and MOB recovery plan should be briefed before departure.

Fire triangle: fuel, heat, oxygen. Fire extinguishers must match the class of fire; fuel fires use foam, CO₂, or dry powder, never water.

Buoyage: safe-water marks have red and white vertical stripes and a spherical topmark; isolated danger marks have two black spheres and a light flashing 2.

IALA special marks are yellow, with a yellow X topmark, and mark special areas such as spoil grounds or pipeline outfalls.

AIS and radar are aids to collision avoidance but do not relieve the skipper of the duty to keep a visual lookout.

Anchoring: scope of about 4–5 times depth in normal conditions; the anchor bearing and transit should be checked to confirm the anchor is holding.

A MOB drill: shout 'man overboard', throw a float, press MOB on GPS, turn back on a reciprocal course, approach from downwind, and recover with the engine in neutral.

Weather: a falling barometer, a rapid drop, or a veering wind in the northern hemisphere often indicates an approaching low or front.

Beaufort scale: force 4 = 11–16 knots, force 5 = 17–21 knots, force 6 = 22–27 knots; whitecaps appear around force 3–4.

VHF: Ch 16 is distress, safety, and calling; Ch 13 is bridge-to-bridge; Ch 70 is DSC only.

A mayday call includes MAYDAY, vessel name and callsign, position, nature of distress, assistance required, persons on board, and any other information.

A chart's title block gives the scale, datum, and units; the compass rose shows true and magnetic north with the variation and its annual change.

Variation is the angle between true and magnetic north at a place; deviation is the error caused by the vessel's own magnetic field.

Conversion: True = Magnetic + Variation (east) or − Variation (west); Magnetic = Compass + Deviation (east) or − Deviation (west).

A position is written as latitude then longitude, e.g. 50° 48.5′ N, 001° 06.2′ W; seconds are not used on charts.

A fix is plotted with a circle and time; a DR position with a semicircle and time; an EP with a square and time.

Tidal stream atlases give the set and rate for a reference port; interpolate between neap and spring rates and between hourly panels.

Plot a position line as a straight line through the observed bearing, with arrows at the ends pointing towards the object observed.

A bearing taken with a hand-bearing compass is a magnetic bearing; convert to true before plotting on the chart.

To find the time of HW at a secondary port: take the standard port HW time, apply the secondary port time difference (which may vary between HW and LW), then apply the height difference to the standard port height.

To find the height at a given time: identify the surrounding HW and LW, calculate the range, find the elapsed time from the nearest HW or LW, and apply the rule of twelfths.

To find the time at which a required height occurs: work out the required rise or fall as a proportion of the range, convert to twelfths, and read off the elapsed time.

Spring and neap ranges: use the standard port's MHWS and MLWS to interpolate between spring and neap tidal stream rates.

Height of tide is measured above chart datum; add it to the charted sounding to get the depth of water.

For a drying height, the actual depth = height of tide − drying height (both above chart datum).

When the tide is falling, subtract the accumulated twelfths from HW height; when rising, add to LW height.

Allow for barometric pressure: roughly 1 cm of tide per hPa above or below 1013 hPa, and for wind setup or set-down in shallow water.

Appraisal: gather charts, almanac, tide tables, tidal stream atlas, weather forecast, and notices to mariners; note availability of ports of refuge.

Planning: lay off the track, mark hazards with clearing bearings, calculate ETAs, and identify waypoints with a safe passing distance.

Execution: keep a log of course, speed, position, and time; compare the EP with fixes and adjust the plan.

Monitoring: check the vessel is on track and on time; a cross-track error or a consistent offset indicates a current or leeway not allowed for.

Leeway: the angle the wind pushes the vessel downwind; it is applied downwind of the course steered.

A safe track keeps a minimum under-keel clearance, typically 10% of draught or 0.5 m, whichever is greater, over charted depths.

A passage plan should include a contingency plan for each leg: an alternative destination or anchorage and abort criteria.

Chart datum and the height of tide must be considered at every waypoint, particularly over bars and in shallow channels.

Power-driven vessel under way: masthead light(s), sidelights (red port, green starboard), and a sternlight; under 12 m may show an all-round white light and sidelights.

Sailing vessel under way: sidelights and sternlight; a sailing vessel may show red over green all-round lights at the masthead.

At anchor: an all-round white light where it can best be seen; a vessel over 50 m also shows a second white light forward.

NUC (not under command): two all-round red lights in a vertical line, and two black balls by day.

RAM (restricted in ability to manoeuvre): red-white-red all-round lights in a vertical line, and a black ball-diamond-ball shape by day.

Constrained by draught: three all-round red lights in a vertical line, and a cylinder by day.

Fishing vessel trawling: two all-round lights in a vertical line, upper green and lower white, and two cones point-to-point by day.

A vessel at anchor or aground shows the anchor light; a vessel aground also shows two all-round red lights in a vertical line.

Before departure: check the weather, file a passage plan with a shore contact, brief the crew on MOB and fire drills, and check lifejackets and harnesses.

Safety equipment: lifejackets for every person on board, harnesses and tethers, flares in date, a first-aid kit, a fire extinguisher, a torch, and a VHF radio.

A lifebuoy with a light and danbuoy should be ready at the helm for immediate MOB deployment.

Hypothermia: treat with gradual warming, remove wet clothing, and do not give alcohol; seek medical advice via VHF or DSC.

Fire: raise the alarm, stop the engine if safe, close fuel valves, use the extinguisher at the base of the fire, and prepare to abandon ship.

A grab bag should contain water, flares, a handheld VHF, a first-aid kit, and a torch.

Crew overboard in cold water: the 1-10-1 principle - about 1 minute to control breathing, 10 minutes of useful movement, and 1 hour before unconsciousness.

Weather routing: obtain forecasts before and during the passage, and record actual conditions to compare with the forecast.

A position line is drawn as a single line with a double arrowhead at the observed end; the time is written alongside.

A transferred position line is drawn with a double arrowhead and a single arrowhead at the transferred end, with the time of transfer noted.

A fix is marked with a circle and the time; a DR position with a semicircle; an EP with a square.

A course is drawn with a single arrowhead and labelled with the course in degrees true and the speed.

A ground track is drawn as a continuous line with time marks at each hour.

Bearings are always plotted as true; convert magnetic bearings by applying variation and deviation.

Use parallel rules or a plotter to transfer a bearing from the compass rose to the position; check the rose is the nearest one to the position.

Latitude and longitude scales: read latitude from the left or right edge, longitude from the top or bottom edge.

MHWS: Mean High Water Springs; MLWS: Mean Low Water Springs; MHWN and MLWN are the neap equivalents.

Mean range = MHWS − MLWS; neap range = MHWN − MLWN.

Springs occur about 1–2 days after new or full moon; neaps about 1–2 days after the quarters.

A tidal day is about 24 h 50 min, so high water occurs about 50 minutes later each day.

Diurnal tides have one high and one low water per day; semi-diurnal tides have two of each, of similar height.

Mixed tides have two highs and two lows of unequal height, common on the west coast of North America.

Chart datum is normally LAT; the height of tide is measured from chart datum upwards.

The tidal stream is the horizontal movement of water; the tide is the vertical movement.

A fix from two objects is strongest when the angle between them is near 90°; avoid angles under 30° or over 150°.

A transit gives a position line along the line of the two objects; a second bearing or a depth contour completes the fix.

A running fix is used when only one object is available; transfer the earlier position line by the course and distance run.

A depth contour can be used as a position line when the depth is changing and the contour is well defined.

GPS gives a position in WGS84; charts may use a different datum, so check for a datum shift note on the chart.

Radar ranges to a headland or a buoy can be used as position lines; a range and a bearing give a fix.

A position fix should be taken at every course change and at least hourly in pilotage waters.

A back bearing is the reciprocal of the bearing to the object; it is used to check the vessel's position along a transit.

One short blast: I am altering my course to starboard. Two short: to port. Three short: I am operating astern propulsion.

At least five short and rapid blasts: doubt or danger.

In a narrow channel, a vessel intending to overtake on the starboard side sounds two prolonged blasts followed by one short; on the port side, two prolonged followed by two short.

A vessel approaching a bend in a narrow channel sounds one prolonged blast; a vessel on the other side answers with one prolonged blast.

In restricted visibility, a power-driven vessel making way sounds one prolonged blast every 2 minutes; stopped, two prolonged blasts every 2 minutes.

A sailing vessel in restricted visibility sounds one prolonged and two short blasts every 2 minutes.

A vessel at anchor in restricted visibility sounds one short, one prolonged, one short blast every 2 minutes.

A vessel aground in restricted visibility sounds three blasts - one short, one prolonged, one short - every 2 minutes, and in addition the anchor signal.

Beaufort force 0 = calm (<1 knot); force 3 = gentle breeze (7–10 knots); force 6 = strong breeze (22–27 knots); force 8 = gale (34–40 knots).

A rapid fall in pressure of more than 1 hPa per hour indicates a deepening low and deteriorating weather.

In the northern hemisphere, wind blows counter-clockwise around a low and clockwise around a high; the wind veers as a front passes.

Sea breeze: on a sunny day the land heats faster than the sea, drawing a breeze onshore in the afternoon.

Fog is common when warm moist air passes over cold water; reduce speed and use fog signals.

A squall line ahead of a cold front brings a sudden wind shift, often to the right, and heavy rain.

Wave height depends on wind speed, fetch, and duration; a long fetch with strong wind builds the largest seas.

Tidal stream against wind produces a short, steep sea; wind against tide is a common cause of dangerous conditions over bars.

Speed = distance ÷ time; distance = speed × time; time = distance ÷ speed.

1 knot = 1 nautical mile per hour; 1 NM = 1852 m.

To convert minutes to hours, divide by 60; e.g. 20 minutes = 0.33 hours.

A distance of 3 NM at 6 knots takes 30 minutes.

A vessel running for 1 hour 20 minutes at 5 knots covers 6.7 NM.

Use the latitude scale to measure distance; do not use the longitude scale except at the equator.

A traverse table or plotter can be used to resolve a course and distance into latitude and longitude differences.

Time zones: UTC is used for all chartwork and almanac calculations; local time is UTC plus or minus the zone offset.

Standard ports have full tidal predictions in the almanac; secondary ports have only differences from a standard port.

Secondary port time differences may be different for HW and LW; interpolate if the difference varies with the tide.

Height differences are added to or subtracted from the standard port height; the sign is given in the almanac.

If the secondary port difference is given as a range of values, interpolate between springs and neaps.

The standard port used for a secondary port is named in the almanac; do not assume the nearest port.

Tidal stream atlases give the set and rate for a reference position; interpolate between neap and spring rates.

Use the tidal stream at the middle of the passage leg, not at the start, for a first estimate.

For a long leg, split it into hourly steps and apply the tidal stream for each hour.

Pilotage is navigation in confined waters using visual references, transits, and clearing bearings.

A transit is two objects in line; it gives a position line along the line of the objects and is used to keep the vessel on track.

A clearing bearing is a bearing to a hazard that keeps the vessel on the safe side; it is drawn on the chart as a line from the hazard.

A sector light shows different colours over different arcs; the safe sector is usually white, but confirm from the chart.

Leading lights are two lights in line, often with different colours, used to guide the vessel through a channel.

A safe track through a channel keeps a safe distance from the edges, allowing for the vessel's draught and for squat.

Squat increases with speed and in shallow water; reduce speed in confined channels.

A pilotage plan should include abort points and a contingency anchorage in case the transit is lost.

Under way means not at anchor, not made fast to the shore, and not aground; a vessel can be under way and not making way.

A vessel not under command is unable to manoeuvre as required by the rules because of exceptional circumstances.

A vessel restricted in ability to manoeuvre is working and cannot keep out of the way as required; a list of examples is in Rule 3.

A vessel constrained by draught is a power-driven vessel which, because of her draught, cannot deviate from the course she is following.

A vessel engaged in fishing means fishing with nets, lines, trawls, or other apparatus that restricts manoeuvrability; it does not include trolling.

A vessel engaged in trawling means dragging a net; a vessel engaged in fishing other than trawling means using lines or nets that restrict manoeuvrability.

A sailing vessel is any vessel under sail, provided the propelling machinery is not being used.

A power-driven vessel is any vessel propelled by machinery; a vessel using both sail and machinery is a power-driven vessel.

MAYDAY: distress; PAN PAN: urgency; SECURITE: safety. Each is repeated three times on VHF Ch 16.

A DSC distress alert is sent on Ch 70 with the vessel's MMSI; follow with a voice mayday on Ch 16.

A MAYDAY RELAY is used when a vessel relays another vessel's distress; it is addressed as MAYDAY RELAY and includes the relaying vessel's identity.

Abandon ship: only on the skipper's order; take the grab bag, water, and a radio, and stay with the liferaft.

A liferaft should be boarded dry if possible; cut the painter only when the raft is clear of the sinking vessel.

MOB: shout, throw a float, press MOB on the GPS, and turn back on a reciprocal course; approach from downwind and recover with the engine in neutral.

Fire: raise the alarm, stop the engine, close fuel valves, use the extinguisher at the base of the fire, and prepare to abandon ship if it cannot be controlled.

Hypothermia: gradual warming, remove wet clothing, and do not give alcohol; seek medical advice.

True north is the direction of the geographic North Pole; magnetic north is the direction of the magnetic pole.

Variation is the angle between true and magnetic north at a place; it changes slowly over time and is shown on the compass rose with an annual change.

Deviation is the angle between magnetic north and the compass north caused by the vessel's own magnetic field; it is shown on a deviation card.

To convert from true to magnetic: apply variation east (+) or west (−). To convert from magnetic to compass: apply deviation east (+) or west (−).

To convert from compass to true: apply deviation and variation in the reverse order.

A hand-bearing compass gives a magnetic bearing; a transit taken visually can be compared with the chart to check the compass.

A deviation card is made by swinging the compass and comparing compass bearings with known transits or bearings.

An east variation means magnetic north is east of true north; the mnemonic is 'east is least' for compass-to-true conversion.

A tide rises from 1.0 m at LW to 5.0 m at HW over 6 hours; the range is 4.0 m.

After 1 hour, the rise is 1/12 of 4.0 m = 0.33 m; height = 1.33 m.

After 2 hours, the rise is 3/12 of 4.0 m = 1.0 m; height = 2.0 m.

After 3 hours, the rise is 6/12 of 4.0 m = 2.0 m; height = 3.0 m.

After 4 hours, the rise is 9/12 of 4.0 m = 3.0 m; height = 4.0 m.

After 5 hours, the rise is 11/12 of 4.0 m = 3.67 m; height = 4.67 m.

After 6 hours, the rise is 12/12 of 4.0 m = 4.0 m; height = 5.0 m.

The rule of twelfths assumes a sinusoidal tide and is least accurate at the extremes of the tide.

Course to steer is the course through the water that, combined with the tidal stream, gives the desired course over the ground.

To find the course to steer: plot the tidal stream vector from the start, then a line from the end of the stream to the destination; the direction of that line is the course to steer.

The length of the line from the end of the stream to the destination, divided by the boat speed, gives the time for the passage.

If the tidal stream is on the beam, the course to steer is offset into the stream; if it is ahead or astern, it changes the speed made good.

Leeway is applied downwind of the course steered; it is estimated from the angle between the wake and the course steered.

A single course to steer is an approximation for a long leg; split the leg into hourly steps for accuracy.

The course made good is the actual track over the ground; it is found by plotting fixes.

A plot of the course to steer and the tidal stream is called a vector triangle.

The give-way vessel takes early and substantial action to keep well clear; a series of small alterations is not acceptable.

The stand-on vessel keeps her course and speed but may take action to avoid collision if the give-way vessel is not taking appropriate action.

If collision cannot be avoided by the give-way vessel alone, the stand-on vessel must take the best action to avoid collision.

A power-driven vessel crossing a sailing vessel gives way; a sailing vessel crossing a power-driven vessel is stand-on unless the power-driven vessel is RAM, NUC, or fishing.

An overtaking vessel keeps clear of the overtaken vessel until finally past and clear.

A vessel in a narrow channel keeps to the starboard side of the channel and does not cross the channel if it would impede a vessel that can only navigate within the channel.

A vessel must not anchor in a narrow channel or fairway except in an emergency.

A vessel must not impede the passage of a vessel which can safely navigate only within a narrow channel or fairway.

Anchor scope: about 4–5 times the depth in normal conditions, more in strong wind or a swell.

The anchor should be veered slowly and the vessel should be brought up with the engine astern to set the anchor.

Check the anchor is holding by taking a transit or a bearing to a fixed object and watching for drift.

A danbuoy or anchor buoy marks the anchor position and helps to avoid fouling.

Mooring: approach into the tide or wind, whichever is stronger; use warps and springs to secure the vessel.

A spring line prevents fore-and-aft movement; a breast line holds the vessel close to the pontoon.

A mooring buoy should be picked up with a boat hook and the line led through a fairlead and made fast.

Anchor in a sheltered position with good holding ground, out of the channel, and allow for the swing of the tide.

A chart is a representation of the sea area and adjacent land, showing depths, hazards, aids to navigation, and the coastline.

Soundings are depths below chart datum, in metres or fathoms as stated in the title block.

Drying heights are heights above chart datum, shown with a line under the figure.

Contour lines join points of equal depth; the 10 m contour is a useful guide to the edge of shallow water.

The magenta line on a chart is the boundary of a traffic separation scheme or a prohibited area; check the notes.

A chart's scale determines the level of detail: a large-scale chart shows more detail over a smaller area.

Notices to Mariners update charts; a chart should be corrected before use.

The compass rose on a chart shows true and magnetic north, with the variation and its annual change.

The tidal stream changes direction and rate throughout the tidal cycle; it is strongest at mid-tide and weakest at HW and LW.

The tidal stream is not the same as the tide; the tide is vertical, the stream is horizontal.

Tidal stream atlases give the set and rate for a reference position at each hour of the tidal cycle.

The set is the direction the stream flows towards, in degrees true; the rate is its speed in knots.

For a passage, choose a departure time to catch a favourable stream; this can save hours on a long leg.

A foul stream can more than halve the speed made good; consider timing the passage to avoid it.

The tidal stream at a secondary position can be interpolated from the nearest reference position.

Wind against tide can produce a short, steep sea; avoid river bars and headlands in these conditions.

Appraisal: gather information, assess the vessel and crew, and identify hazards and options.

Planning: lay off the track, calculate the course to steer, ETAs, and tidal heights; identify waypoints and abort points.

Execution: follow the plan, keep a log, and take fixes at every course change.

Monitoring: compare the actual position with the plan and adjust for current, leeway, and weather.

A passage plan should be written down and briefed to the crew before departure.

A contingency plan should cover a change of destination, a port of refuge, and an anchorage.

The plan should include a watch system, a MOB plan, and a fire plan.

A passage plan should consider the vessel's draught, the height of tide, and the under-keel clearance at every waypoint.

Sidelights: red on the port side, green on the starboard side, each showing from dead ahead to 22.5° abaft the beam.

Masthead light: white, showing from dead ahead to 22.5° abaft the beam on both sides, and visible over a greater range than the sidelights.

Sternlight: white, showing from dead astern to 22.5° on each side.

A power-driven vessel under 12 m may show an all-round white light and sidelights instead of masthead and stern lights.

A sailing vessel under way shows sidelights and a sternlight; it may show red over green all-round lights at the masthead.

A vessel at anchor shows an all-round white light where it can best be seen; a vessel over 50 m shows a second white light forward.

A vessel aground shows the anchor light and two all-round red lights in a vertical line.

A vessel not under command shows two all-round red lights in a vertical line and two black balls by day.

Lifejackets should be fitted with a light, a whistle, and a crotch strap; check they are in date and the cylinder is charged.

A harness and tether should be worn at night, in strong winds, and when working on deck.

A jackstay or a safety line should be rigged along the deck for clip-on points.

A MOB should be briefed before departure: shout, throw, press MOB, turn back, approach from downwind, and recover.

A danbuoy and a lifebuoy with a light should be ready at the helm.

A grab bag should be kept in the cockpit with water, flares, a radio, and a first-aid kit.

Fire extinguishers should be checked and in date; a fire blanket should be in the galley.

A first-aid kit should include seasickness tablets, painkillers, and a thermal blanket.

A fix from two bearings is plotted at the intersection of the two position lines; the angle of cut should be near 90°.

A three-point fix uses three objects; a small cocked hat indicates a good fix.

A running fix uses one object and the course and distance run between two bearings.

A transit and a bearing give a fix; the transit is a position line along the line of the two objects.

A depth contour can be used as a position line when the depth is changing and the contour is well defined.

Radar ranges and bearings to a headland or a buoy give a fix.

GPS gives a position in WGS84; check the chart datum and any datum shift note.

A fix should be taken at every course change and at least hourly in pilotage waters.

Charted depth is the depth below chart datum; the actual depth is charted depth plus height of tide.

Height of tide is measured from chart datum upwards; it is found from tide tables or by the rule of twelfths.

Drying height is the height of a rock or shoal above chart datum; the actual depth over it is height of tide minus drying height.

Under-keel clearance = charted depth + height of tide − draught.

Allow for squat: it increases with speed and in shallow water, and reduces under-keel clearance.

Allow for a margin of safety: at least 10% of draught or 0.5 m, whichever is greater.

The height of tide at the time of the passage is what matters, not the height at HW.

A falling tide reduces the depth; plan to pass a shallow bar near HW if possible.

A buoy is a floating aid to navigation; it is moored to the seabed and may move slightly.

A beacon is a fixed aid to navigation, often a post or a tower.

A lighthouse is a major aid with a light of high intensity, often with a sector or a flashing character.

A sector light shows different colours over different arcs; the safe sector is usually white, but confirm from the chart.

A leading light is one of two lights in line, used to guide the vessel through a channel.

A transit is two objects in line; it gives a position line along the line of the objects.

A clearing bearing is a bearing to a hazard that keeps the vessel on the safe side.

A cardinal mark indicates the safe quadrant; the light flashes match the clock face.

Rule 19 applies in restricted visibility; the steering and sailing rules (12–18) do not apply.

A vessel must proceed at a safe speed adapted to the reduced visibility and the traffic density.

A power-driven vessel making way sounds one prolonged blast every 2 minutes.

A power-driven vessel stopped sounds two prolonged blasts with a 2-second interval every 2 minutes.

A sailing vessel sounds one prolonged and two short blasts every 2 minutes.

A vessel at anchor sounds one short, one prolonged, one short blast every 2 minutes.

A vessel aground sounds three blasts - one short, one prolonged, one short - every 2 minutes.

Radar should be used to detect other vessels, but a visual lookout must also be kept.

A shipping forecast gives wind direction and force, sea state, weather, and visibility for a sea area.

A gale warning is issued when winds of force 8 or more are expected.

A strong wind warning is issued for force 6 or 7.

A small craft warning is issued for force 6 or more in some countries.

A rapid fall in pressure of more than 1 hPa per hour indicates a deepening low.

A veering wind in the northern hemisphere often follows the passage of a cold front.

A backing wind often precedes a warm front or a low.

Fog is common when warm moist air passes over cold water; reduce speed and use fog signals.

A course is plotted from the start position with a single arrowhead and labelled with the course in degrees true and the speed.

The course steered is the course through the water; the course made good is the track over the ground.

A ground track is drawn as a continuous line with time marks at each hour.

A position line is drawn as a single line with a double arrowhead at the observed end; the time is written alongside.

A transferred position line is drawn with a double arrowhead and a single arrowhead at the transferred end.

A fix is marked with a circle and the time; a DR position with a semicircle; an EP with a square.

Bearings are always plotted as true; convert magnetic bearings by applying variation and deviation.

Use parallel rules or a plotter to transfer a bearing from the compass rose to the position.

Tide tables give the time and height of HW and LW for each standard port for each day of the year.

Heights are given above chart datum; times are given in UTC or local time as stated.

Secondary port differences are given in a separate table; they are applied to the standard port predictions.

Time differences may be different for HW and LW; height differences are added or subtracted.

Spring and neap ranges are given for each standard port; use them to interpolate between spring and neap tidal stream rates.

The tidal stream atlas gives the set and rate for a reference position at each hour of the tidal cycle.

Interpolate between neap and spring rates for a tide between the two.

Use the tidal stream at the middle of the passage leg for a first estimate.

A waypoint is a position on the chart that the vessel is steering towards; it should be in safe water.

A route is a series of waypoints connected by legs; each leg should be checked for hazards and depth.

A waypoint should be placed with a safe passing distance from a hazard, not on the hazard.

A route should be checked for cross-track error and for the effect of current and leeway.

A route should include an alternative destination and an abort point.

A route should be entered into the GPS and checked against the chart.

A route should be briefed to the crew, with the expected course, speed, and ETA for each leg.

A route should be monitored by comparing the GPS position with the chart and with visual references.

The COLREGS apply to all vessels on the high seas and in all waters connected therewith navigable by seagoing vessels.

Nothing in the rules exonerates a vessel from the consequences of any neglect to comply with the rules.

A vessel must take positive action in ample time and with due regard to the observance of good seamanship.

A vessel must not impede the passage of another vessel when required by the rules.

A vessel must keep a proper lookout by sight and hearing and by all available means.

A vessel must proceed at a safe speed at all times.

A vessel must use all available means to determine if a risk of collision exists.

A vessel must take avoiding action in ample time and with due regard to the observance of good seamanship.

Reduce sail before the wind increases; reef early and shorten sail in good time.

Heave to or run before the wind with a sea anchor or a drogue if the weather is too heavy to make progress.

Keep the vessel closed up, secure loose gear, and rig jackstays and harnesses.

Avoid a beam-on sea; take the sea on the bow or quarter.

Reduce speed in heavy weather to avoid pounding and to keep the propeller in the water.

Check the barometer and the forecast regularly; a rapid fall indicates a deepening low.

Prepare a grab bag and a liferaft in case of abandoning ship.

Keep the crew rested and fed; fatigue is a major cause of error.

Dead reckoning (DR) uses the course steered and the distance run through the water, with no allowance for current or leeway.

Estimated position (EP) adds the estimated leeway and tidal stream to the DR position.

The DR position is marked with a semicircle and the time; the EP with a square and the time.

The distance run is taken from the log or from speed × time.

Leeway is the angle the wind pushes the vessel downwind; it is applied downwind of the course steered.

The tidal stream is applied as a vector from the DR position to give the EP.

A fix is more reliable than an EP; take a fix whenever possible.

The difference between the EP and the fix shows the error in the estimated current and leeway.

Find the HW and LW times and heights that bracket the required time.

Calculate the range: HW height − LW height.

Find the elapsed time from the nearest HW or LW.

Apply the rule of twelfths to find the rise or fall.

Add the rise to the LW height or subtract the fall from the HW height.

Check that the result is between the LW and HW heights.

Allow for barometric pressure: about 1 cm per hPa above or below 1013 hPa.

Allow for wind setup or set-down in shallow water.

ETA = departure time + (distance ÷ speed).

Distance = speed × time; time = distance ÷ speed.

Speed made good = distance over the ground ÷ elapsed time.

Compare the speed made good with the boat speed to detect a favourable or adverse stream.

Allow for a foul stream by increasing the speed or by choosing a different departure time.

Allow for leeway in the ETA by using the speed made good, not the boat speed.

A passage plan should include an ETA for each waypoint and for the destination.

Update the ETA as the passage progresses and inform the shore contact of any significant change.

IALA Region A: port-hand marks are red cans, starboard-hand marks are green cones.

IALA Region B: port-hand marks are green cans, starboard-hand marks are red cones.

Cardinal marks: north both cones up, south both down, east base-to-base, west point-to-point.

Cardinal lights flash the clock face: N 1, E 3, S 6, W 9.

Safe-water marks have red and white vertical stripes and a spherical topmark.

Isolated danger marks have two black spheres and a light flashing 2.

Special marks are yellow with a yellow X topmark.

A sector light shows different colours over different arcs; the safe sector is usually white.

MAYDAY is used when a vessel or person is in grave and imminent danger and requires immediate assistance.

PAN PAN is used when a vessel or person is in urgency but not in immediate danger.

SECURITE is used for safety messages, such as a navigation hazard or a weather warning.

A DSC distress alert is sent on Ch 70 with the vessel's MMSI; follow with a voice mayday on Ch 16.

A MAYDAY RELAY is used when a vessel relays another vessel's distress.

A distress signal includes red parachute flares, orange smoke, and the spoken word MAYDAY.

A urgency signal includes PAN PAN and the spoken word PAN PAN.

A safety signal includes SECURITE and the spoken word SECURITE.

Latitude is the angle north or south of the equator, from 0° to 90°.

Longitude is the angle east or west of Greenwich, from 0° to 180°.

1 minute of latitude = 1 nautical mile.

1 minute of longitude = 1 NM × cos(latitude).

Latitude is read from the left or right edge of the chart; longitude from the top or bottom edge.

A position is written as latitude then longitude, e.g. 50° 48.5′ N, 001° 06.2′ W.

The equator is 0° latitude; the prime meridian is 0° longitude.

The poles are at 90° N and 90° S; longitude is undefined at the poles.

Spring tides occur near new and full moon, about 1–2 days later.

Neap tides occur near the first and third quarters, about 1–2 days later.

Spring range is larger than neap range.

Mean range = MHWS − MLWS; neap range = MHWN − MLWN.

The tidal stream is stronger at springs than at neaps.

Interpolate between spring and neap rates for a tide between the two.

A tidal day is about 24 h 50 min, so high water occurs about 50 minutes later each day.

Diurnal tides have one high and one low water per day; semi-diurnal tides have two of each.

Charts and publications should be corrected to the latest notice to mariners.

The almanac gives tide tables, tidal stream atlases, and port information.

The pilot book gives local information on harbours, anchorages, and hazards.

The cruising guide gives information on marinas, fuel, and water.

The weather forecast should be obtained before departure and during the passage.

A passage plan should be written down and briefed to the crew.

A log should be kept of course, speed, position, and time.

A shore contact should be given the passage plan and the ETA.

A steady bearing and decreasing range indicates a risk of collision.

If in doubt, assume a risk of collision exists.

Take early and substantial action to keep well clear.

A series of small alterations is not acceptable.

The give-way vessel should pass astern of the stand-on vessel.

The stand-on vessel keeps her course and speed but may act if the give-way vessel is not taking appropriate action.

If collision cannot be avoided by the give-way vessel alone, the stand-on vessel must take the best action to avoid collision.

A vessel must not impede the passage of another vessel when required by the rules.

Brief the crew on the passage plan, the watch system, and the expected weather.

Brief the crew on MOB, fire, and abandon ship procedures.

Show the crew where the lifejackets, harnesses, flares, and first-aid kit are kept.

Show the crew how to use the VHF radio and the DSC distress alert.

Show the crew how to start and stop the engine and how to steer.

Show the crew where the seacocks, fuel valves, and battery switches are.

Check that the crew are fit to sail and are not seasick.

Check that the crew have suitable clothing and footwear.

A rock awash is shown by a cross or a star; a rock below the surface by a sounding with a line under it.

A wreck is shown by a symbol with the depth over it; a dangerous wreck may be marked by a buoy.

A drying height is shown with a line under the figure.

A contour line joins points of equal depth; the 10 m contour is a useful guide.

A magenta line marks the boundary of a traffic separation scheme or a prohibited area.

A buoy is shown by a symbol with its colour and light character.

A lighthouse is shown by a star with a light character.

A transit is shown by two objects in line, often with a dashed line.

The tidal stream is a vector with a set (direction) and a rate (speed).

The set is the direction the stream flows towards, in degrees true.

The rate is the speed of the stream in knots.

The tidal stream changes direction and rate throughout the tidal cycle.

It is strongest at mid-tide and weakest at HW and LW.

Use the tidal stream at the middle of the passage leg for a first estimate.

Split a long leg into hourly steps and apply the tidal stream for each hour.

The tidal stream at a secondary position can be interpolated from the nearest reference position.

A landfall is the first sight of land at the end of a passage.

Plan the landfall to be made in daylight and in good visibility.

Identify the landfall by a transit, a lighthouse, or a prominent landmark.

Allow for the effect of current and leeway on the landfall position.

Take a fix as soon as possible and compare it with the DR position.

Have a contingency plan in case the landfall is not made as planned.

Reduce speed in poor visibility and use fog signals.

Keep a proper lookout by sight and hearing.

A vessel engaged in trawling shows two all-round lights in a vertical line, upper green and lower white.

By day, a vessel engaged in trawling shows two cones point-to-point.

A vessel engaged in fishing other than trawling shows two all-round lights in a vertical line, upper red and lower white.

By day, a vessel engaged in fishing other than trawling shows a black ball.

A vessel engaged in fishing may show a light or shape to indicate the direction of the gear.

A vessel engaged in fishing is a vessel to which other vessels must give way.

A vessel engaged in fishing is not a vessel restricted in ability to manoeuvre unless the gear restricts manoeuvrability.

A vessel engaged in fishing should be given a wide berth.

Shout 'man overboard' and throw a float or a lifebuoy.

Press the MOB button on the GPS to mark the position.

Turn back on a reciprocal course, or use the Williamson turn.

Approach the casualty from downwind and recover with the engine in neutral.

Keep the casualty in sight and appoint a lookout.

Use a throwing line or a recovery sling to bring the casualty alongside.

Be prepared to recover the casualty with a halyard or a crane.

Treat for hypothermia and seek medical advice.

Take the bearing with a hand-bearing compass and convert to true.

Plot the bearing as a position line from the object.

Repeat for a second and third object.

The intersection of the position lines is the fix.

Mark the fix with a circle and the time.

Check the angle of cut; aim for near 90°.

A small cocked hat indicates a good fix.

Compare the fix with the DR position to check for current and leeway.

Standard port HW at 12:00 UTC, height 4.0 m; LW at 18:00 UTC, height 1.0 m.

Secondary port time difference: HW +20 minutes, LW +10 minutes.

Secondary port height difference: HW −0.2 m, LW +0.1 m.

Secondary port HW: 12:20 UTC, height 3.8 m.

Secondary port LW: 18:10 UTC, height 1.1 m.

Range at the secondary port: 3.8 − 1.1 = 2.7 m.

Apply the rule of twelfths to find the height at a given time.

Check that the result is between the LW and HW heights.

Choose a departure time to catch a favourable tidal stream.

Plan to pass a shallow bar near HW if possible.

Avoid a foul stream on a long leg; it can more than halve the speed made good.

Allow for the effect of wind against tide on the sea state.

Plan the landfall to be made in daylight and in good visibility.

Allow for a contingency in case of delay.

Update the ETA as the passage progresses.

Inform the shore contact of any significant change.

A vessel in a narrow channel keeps to the starboard side of the channel.

A vessel must not cross the channel if it would impede a vessel that can only navigate within the channel.

A vessel must not anchor in a narrow channel or fairway except in an emergency.

A vessel must not impede the passage of a vessel which can safely navigate only within a narrow channel or fairway.

A vessel approaching a bend in a narrow channel sounds one prolonged blast.

A vessel on the other side of the bend answers with one prolonged blast.

A vessel intending to overtake in a narrow channel sounds two prolonged blasts followed by one short (starboard) or two short (port).

A vessel must take early and substantial action to keep well clear.

The fire triangle: fuel, heat, oxygen.

Remove one of the three to extinguish a fire.

Fuel fires use foam, CO₂, or dry powder; never water.

Electrical fires use CO₂ or dry powder; never water.

Check the engine compartment for fuel leaks and keep it clean.

Keep a fire blanket in the galley and a fire extinguisher near the engine.

Close fuel valves and battery switches if safe to do so.

Prepare to abandon ship if the fire cannot be controlled.

Chart datum is normally Lowest Astronomical Tide (LAT).

Soundings are depths below chart datum.

Drying heights are heights above chart datum.

The height of tide is measured from chart datum upwards.

The actual depth = charted depth + height of tide.

The actual depth over a drying height = height of tide − drying height.

Allow for under-keel clearance of at least 10% of draught or 0.5 m.

Check the chart datum note in the title block.

Hour 1: 1/12 of the range.

Hour 2: 2/12 of the range.

Hour 3: 3/12 of the range.

Hour 4: 3/12 of the range.

Hour 5: 2/12 of the range.

Hour 6: 1/12 of the range.

Total: 12/12 of the range.

The rule assumes a sinusoidal tide and is least accurate at the extremes.

Cross-track error is the distance between the vessel's actual position and the planned track.

It is caused by current, leeway, or a steering error.

A consistent cross-track error indicates a current or leeway not allowed for.

Correct the course to steer to reduce the cross-track error.

Monitor the cross-track error at each fix.

A large cross-track error may require a new course to steer.

Use a transit or a clearing bearing to check the cross-track error.

Keep a record of the cross-track error in the log.

An overtaking vessel keeps clear of the overtaken vessel.

The overtaken vessel holds her course and speed.

A vessel is overtaking if she is coming up on another vessel from a direction more than 22.5° abaft her beam.

If in doubt, assume she is overtaking and keep clear.

The overtaking vessel must keep clear until finally past and clear.

In a narrow channel, the overtaking vessel sounds two prolonged blasts followed by one or two short blasts.

The overtaken vessel answers with one prolonged, one short, one prolonged, one short blast.

A vessel must not overtake if it would impede a vessel that can only navigate within the channel.

VHF Ch 16 is the distress, safety, and calling channel.

VHF Ch 70 is the DSC channel; do not use it for voice.

VHF Ch 13 is the bridge-to-bridge channel.

A DSC distress alert is sent on Ch 70 with the vessel's MMSI.

Follow the DSC alert with a voice mayday on Ch 16.

A MAYDAY RELAY is used when a vessel relays another vessel's distress.

A PAN PAN is used for urgency; a SECURITE for safety.

Keep a listening watch on Ch 16 while at sea.

A bearing is the direction of an object from the vessel, in degrees true.

A transit is two objects in line; it gives a position line along the line of the objects.

A back bearing is the reciprocal of the bearing to the object.

A clearing bearing is a bearing to a hazard that keeps the vessel on the safe side.

A leading light is one of two lights in line, used to guide the vessel through a channel.

A sector light shows different colours over different arcs.

A hand-bearing compass gives a magnetic bearing.

Convert magnetic bearings to true before plotting.

High pressure depresses the height of tide; low pressure raises it.

The effect is about 1 cm per hPa above or below 1013 hPa.

A deep low can raise the tide by 0.3 m or more.

Wind setup can raise the tide in shallow water or in a bay.

Wind set-down can lower the tide on a lee shore.

Allow for the barometric effect in shallow water and over bars.

Check the pressure tendency in the forecast.

A rapid fall in pressure indicates a deepening low.

Identify the landfall and the entry to the harbour.

Lay off the track and mark hazards with clearing bearings.

Identify transits and leading lights.

Note the minimum depths and the height of tide.

Identify abort points and a contingency anchorage.

Brief the crew on the plan.

Keep a proper lookout and take fixes at every course change.

Reduce speed in poor visibility and use fog signals.

The stand-on vessel keeps her course and speed.

She may take action to avoid collision if the give-way vessel is not taking appropriate action.

If collision cannot be avoided by the give-way vessel alone, she must take the best action to avoid collision.

She should sound at least five short and rapid blasts if in doubt.

She should not alter course to port for a vessel on her own port side.

She should not alter course towards an overtaking vessel.

She should keep a proper lookout and monitor the risk of collision.

She should be prepared to take action if the give-way vessel does not.

Choose a sheltered position with good holding ground.

Anchor out of the channel and allow for the swing of the tide.

Use a scope of about 4–5 times the depth.

Veer the anchor slowly and set it with the engine astern.

Check the anchor is holding by taking a transit or a bearing.

Use a danbuoy or an anchor buoy to mark the anchor.

Keep an anchor watch in a strong wind or a swell.

Be prepared to weigh anchor and move if the anchor drags.

Speed = distance ÷ time.

Distance = speed × time.

Time = distance ÷ speed.

1 knot = 1 nautical mile per hour.

1 NM = 1852 m.

Convert minutes to hours by dividing by 60.

Use the latitude scale to measure distance.

A traverse table or plotter resolves a course and distance into latitude and longitude differences.

The tidal stream atlas gives the set and rate for a reference position at each hour of the tidal cycle.

Interpolate between neap and spring rates for a tide between the two.

Use the tidal stream at the middle of the passage leg for a first estimate.

Split a long leg into hourly steps and apply the tidal stream for each hour.

The tidal stream is strongest at mid-tide and weakest at HW and LW.

The set is the direction the stream flows towards.

The rate is the speed of the stream in knots.

The tidal stream at a secondary position can be interpolated from the nearest reference position.

Reduce speed to a safe speed.

Use fog signals and keep a listening watch.

Use radar and AIS to detect other vessels.

Keep a proper visual lookout as well.

Plot the position frequently and compare with the DR position.

Be prepared to anchor if the visibility does not improve.

Avoid confined waters and headlands in fog.

Use a GPS and a chart plotter to monitor the position.

A sailing vessel under way shows sidelights and a sternlight.

She may show red over green all-round lights at the masthead.

A sailing vessel under 7 m may show a white torch or lantern if practicable.

A sailing vessel under way with the engine on is a power-driven vessel and shows the appropriate lights.

A sailing vessel at anchor shows an all-round white light.

A sailing vessel aground shows the anchor light and two all-round red lights.

A sailing vessel not under command shows two all-round red lights.

A sailing vessel restricted in ability to manoeuvre shows red-white-red lights.

Shout 'man overboard' and throw a float.

Press the MOB button on the GPS.

Turn back on a reciprocal course or use the Williamson turn.

Approach the casualty from downwind.

Recover with the engine in neutral.

Use a throwing line or a recovery sling.

Be prepared to recover with a halyard or a crane.

Treat for hypothermia and seek medical advice.