Night and Fog Pilotage

Prerequisites

• Day Skipper level night sailing: recognition of navigation lights on vessels, buoyage (IALA Region A) and basic light characteristics.
• Coastal Skipper course entry experience: 15 days, 2 days as skipper, 300 miles and 8 night hours. The Yachtmaster Coastal exam requires 12 night hours and you may be asked to bring the boat into harbour at night during the exam.
• Completion of the earlier Coastal Skipper lessons on pilotage in unfamiliar waters, radar and AIS (parallel indexing, CPA/TCPA) and COLREGs in restricted visibility.

Learning Objectives

This lesson covers the night, pilotage and restricted-visibility elements of the RYA Coastal Skipper / Yachtmaster Offshore shorebased syllabus (lights, buoyage, electronic aids, pilotage) and the Yachtmaster Coastal practical, where the candidate may be asked to enter an unfamiliar harbour at night and to handle fog. By the end you will be able to:

• Identify lights by their characteristics, and use sector lights, leading lights and directional lights as position lines. (RYA syllabus: lights and light characteristics, pilotage by lights.)
• Calculate the geographical range and rising or dipping range of a light, correct it for the height of tide, and use it as a position fix. (RYA syllabus: rising and dipping distance, nominal and geographic range.)
• Recognise IALA Region A buoyage lights and the rhythm that identifies each mark. (RYA syllabus: buoyage.)
• Preserve night vision and run an effective lookout and watch system at night and in fog. (RYA syllabus: night sailing, watchkeeping.)
• Prepare and execute a night pilotage plan into an unfamiliar harbour, including an abort plan. (RYA syllabus: pilotage plans, harbour entry at night.)
• Decide on a safe speed and a strategy when visibility closes in, using radar, depth contours and fog signals, and carry out blind pilotage with a cross-tide allowance. (RYA syllabus: restricted visibility, radar pilotage, Rules 6 and 19.)
• Make and recognise the correct sound signals in fog and from navigational aids. (RYA syllabus: Rule 35 and fog signals.)
• Recognise and avoid the common errors of night and fog navigation.

Why Night and Fog Are Different

By day, a skipper takes in a huge amount of information at a glance: the shape of the land, the colour of the water, the shape and topmark of a buoy, the aspect of another vessel. At night, almost all of that is reduced to points of light against black, and in fog, even the lights disappear. The navigation principles are unchanged, but you must:

• plan more thoroughly, because there is less time and light to work things out on the way in;
• use every available source (lights, compass bearings, depth, radar, GPS, sound) and cross-check them;
• accept larger safety margins: stand further off dangers, slow down, and have a pre-planned abort.

Light Characteristics

Every lighthouse, lit buoy and beacon has a characteristic printed on the chart and in the almanac. Example: Fl(3) WR 15s 26m 18/14M means groups of 3 flashes, white and red sectors, repeated every 15 seconds, 26 m above MHWS, nominal range 18 miles (white) and 14 miles (red).

Cardinal marks in IALA Region A use white quick or very quick flashing lights, coded like a clock face: north continuous; east 3 flashes; south 6 flashes plus a long flash; west 9 flashes. Isolated danger marks show Fl(2) white; safe water marks Iso, Oc, LFl 10s or Mo(A) white; special marks yellow; port-hand marks red and starboard-hand green in any rhythm other than those reserved above.

Identifying a light

1. From the plan, list the lights you expect to see, their characteristics, and the bearing and time when they should appear.
2. When a light appears, take a compass bearing and time its period with a stopwatch, counting from the start of one group to the start of the next. Count at least three cycles.
3. Check the colour, including whether it changes (sector light) as you move.
4. Confirm it against the chart and the expected bearing. If it does not match, do not "make it fit".

Background lights from towns, cars and moored ships make identification harder. An occulting light can look like a fixed light at first; a quick flasher among street lights is easily lost.

Range of a light and rising or dipping

The almanac gives a light's nominal range: how far it can be seen in clear visibility (meteorological visibility of 10 miles), ignoring the curvature of the earth. Whether you can actually see it also depends on its geographical range, set by the height of the light and the height of your eye:

Geographical range in miles is approximately 2.08 multiplied by (the square root of the light's height in metres plus the square root of the eye height in metres).

Example: a lighthouse 49 m above MHWS, eye height 2.25 m. Square root of 49 is 7.0, of 2.25 is 1.5. Range = 2.08 x 8.5 = 17.7 miles. If its nominal range is 20 miles and visibility is good, you will see the light itself appear above the horizon ("rise") at about 17.7 miles. At that moment, a compass bearing of the light plus the 17.7 mile range gives a fix. Strictly, light heights are above MHWS, so at lower tides the light is slightly further above the sea and appears a little sooner; the error is small for coastal work. Before the light itself rises you may see its "loom" lighting the clouds, which gives a bearing but not a range.

If the nominal range is less than the geographical range, the light will simply fade in rather than rise, and you cannot use rising and dipping.

Sector lights

A sector light shows different colours over different arcs, defined in the almanac by true bearings from seaward towards the light. Typically the white sector covers the safe approach and red and green sectors cover dangers on either side. Some sector lights use red over a hazard and white elsewhere.

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The moment the colour changes, you are on the charted boundary bearing: an accurate position line without even taking a compass bearing. Boundaries are not perfectly sharp; there is a narrow band, perhaps a degree or two, where the colours blend or the light looks white-pink. Use the middle of the white sector, not its edge.

Directional lights (Dir) have a very narrow white sector, often only a degree or two wide, with red and green on either side, sometimes with "intensified" sectors. They mark a channel like a leading line. In UK practice the green sector is usually on the starboard side of the approach and the red on the port side, but always check the chart: the convention is not universal.

Leading lights

Two lights, the rear one higher than the front, which are in line (one directly above the other) when you are on the charted leading line.

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If the rear light appears to the right of the front light, you are to the left of the line: move to the right (towards the higher light). "Follow the rear light" or "steer towards the top light" helps you remember. Check the compass course matches the charted leading line bearing to confirm you have the right pair, as some harbours have several pairs. Leading lights often have the same characteristic (for example both Oc 4s) or the front fixed and rear occulting; some are synchronised.

Light Calculations and Buoyage at Night

Worked example: rising range corrected for the height of tide

Light heights on charts are given above MHWS. If the tide is lower than MHWS the light stands higher above the water, so it can be seen from further away.

A light at 30 m above MHWS has a nominal range of 20 miles. MHWS is 5.0 m (height above chart datum); at the time of observation the height of tide is 2.0 m. The tide is 3.0 m below MHWS so the effective height of the light above the water is 30 + 3.0 = 33 m. Eye height is 3 m.

• Square root of 33 = 5.74; square root of 3 = 1.73.
• Geographical range = 2.08 x (5.74 + 1.73) = 2.08 x 7.47 = 15.5 miles.
• The nominal range of 20 miles is greater than 15.5, so the light will rise at 15.5 miles.

If you see the light appear at the moment the crew calls "light in sight" at 2100, and the light bears 285 degrees (magnetic variation 2 degrees West, so 283 degrees True), the position is 15.5 miles from the light along the reciprocal bearing of 103 degrees True. A single bearing plus a range gives a fix. Using a dipping observation is exactly the reverse: the light disappears as you steam away; record the time and the bearing at the moment the light dips.

Which range applies? Luminous or nominal

• Nominal range assumes meteorological visibility of 10 miles; it ignores the curvature of the Earth.
• Luminous range is the range in the actual visibility on the night; it can be found from the almanac's luminous range diagram if you know the visibility and nominal range. In haze the luminous range is shorter than nominal.
• Geographical range is limited by height and the Earth's curvature. You see a light out to whichever is the smaller of luminous and geographical range.

Light rhythms of IALA Region A marks

Buoyage is anchored on the direction of buoyage: for a harbour entrance, it is normally "from seaward to the harbour". Check the chart for arrows; at the junction of two systems of buoyage, trust the chart.

Common misidentification traps

• Fixed or occulting lights among street lights are easily lost; a quick flasher looks like a steady light at long range.
• Colours change with distance and haze; a white light low on the horizon can look red or yellow. Wait until the light is clear before fixing a position on it.
• Lights hidden by land or buildings appear and disappear; do not assume that an expected light that has not appeared is faulty. Check the angle of cut-off in the almanac.
• Lights of anchored or moving vessels, shore signs and cranes may mimic navigation lights. A light that moves relative to the background is not a lighthouse.
• Light out of service: read the Notices to Mariners, local almanac updates and MSI before the passage; a charted light can be extinguished.

Night Vision

The eye adapts to darkness by switching from cone cells (colour, detail, daylight) to rod cells (sensitive, greyscale). Full dark adaptation takes 20 to 30 minutes, and a single exposure to bright white light destroys most of it in a second.

• Use dim red light below and on deck. A red head torch is part of every crew member's kit.
• Turn chartplotter, radar and instrument displays to night mode and the lowest readable brightness.
• Keep the chart table light shielded; close the curtain or chart table hood.
• Allow the oncoming watch 10 to 20 minutes in the cockpit before taking over.
• Rods are concentrated outside the centre of the eye, so to see a faint light, look slightly to one side of it, and sweep slowly rather than staring.
• Binoculars of 7x50 gather a lot of light and are the standard night glasses.
• Fatigue, cold, seasickness and smoking all reduce night vision.

Lookout at Night

Rule 5 requires a proper lookout by sight and hearing and all available means. At night the helmsman, concentrating on the compass, is a poor lookout.

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• Post a dedicated lookout in addition to the helmsman whenever traffic or navigation demands it, and always in pilotage and restricted visibility.
• Sweep the full horizon, especially behind the genoa and astern; the area hidden by the headsail is where collisions come from.
• Report lights in a standard form: what, bearing, range estimate, change. For example: "Ship's lights, white over white with a red, bearing 040, about 3 miles, bearing steady."
• Take repeated compass bearings of any approaching vessel; a steady bearing means risk of collision.
• Use radar and AIS to supplement, not replace, your eyes. Many small fishing vessels and yachts do not transmit AIS.
• Rotate the lookout regularly; in poor visibility and cold, 30 minutes of concentrated lookout is a sensible maximum.

Reading vessel lights

At night you must decode aspect (which way a vessel is heading) as well as type. Two masthead lights in line with the lower (forward) light directly under the higher (aft) one and both sidelights visible means a power-driven vessel heading straight towards you. If the forward masthead light is to the left of the aft one, she is showing you her starboard side and heading to your right. Lights high above a dark mass with many deck lights may be a ship at anchor, not underway; check for movement on radar.

Planning a Night Pilotage

A night entry into an unfamiliar harbour is examined at Yachtmaster Coastal and is one of the most demanding skipper tasks. Prepare it alongside in daylight:

1. Study the large-scale chart, almanac and pilot book. Note all lights with characteristics, sectors and heights, unlit marks and dangers, depths and the tidal height at arrival.
2. Choose a route that uses lit marks, sector lights and leading lines. Where unlit dangers exist, plan clearing bearings on lights and a safe depth contour.
3. Write a pilotage plan in a notebook or on a card at the chart table: each leg with the mark or light to look for, its characteristic, the course to steer, the distance and the next turning point. Many skippers draw a simplified sketch as the lights will appear.
4. Plan the arrival time: tidal height for depth, tidal stream (avoid a strong cross-set in a narrow entrance), and whether daylight would be safer.
5. Brief the crew before the approach: who steers, who navigates, who keeps lookout, who reports depth, what lights to expect, and what will trigger an abort.
6. Have an escape plan: a safe heading out to sea and an alternative harbour or anchorage.

Using depth contours

At night, the sounder is an invaluable confirmation of position. A known depth contour on the chart can act as a handrail: follow the 10 m line along a coast, or set a shallow alarm so you know when you have strayed inshore.

Correct the charted depth for the height of tide, and remember that the sounder reads from the transducer, not the keel or the surface, unless an offset has been set. A sudden change in depth that does not match the chart is a reason to stop and re-fix.

Restricted Visibility

Safe speed

Rule 6 requires a safe speed at all times, and Rule 19 specifically in restricted visibility. A widely used rule of thumb is that you should be able to stop within half the distance you can see, because another vessel may be approaching at a similar speed.

Factors include the visibility, traffic density, your stopping distance and turning ability, the quality of your radar picture (and the fact that you may be a poor radar target to others), sea state, and the proximity of dangers. In visibility of 100 m, even 4 knots is too fast to avoid an unseen vessel. Slowing down also gives time to hear and interpret fog signals.

Preparing for fog

When fog is forecast or seen approaching (a hazy band on the horizon, the far shore disappearing, a drop in air temperature near cold water in spring and early summer, typical of advection fog):

1. Fix your position accurately before it arrives and write it in the log.
2. Put on lifejackets, hoist a radar reflector (or switch on the active radar target enhancer), and turn on navigation lights.
3. Start the engine and keep it ready for immediate manoeuvre.
4. Post lookouts, one forward if possible to listen away from engine noise, and one aft.
5. Switch on radar and AIS; set guard zones.
6. Begin sounding the correct fog signal (see below).
7. Decide on strategy.

Strategy: where to be in fog

The greatest danger is from large vessels. Shipping keeps to deep water, so a yacht is often safest in water too shallow for ships but deep enough for you, away from lanes, channels and harbour entrances. Options:

• Stay at sea in open water away from traffic and dangers, heave to or motor slowly, and wait for the fog to clear. Suitable if you are clear of shipping routes.
• Head for shallow water out of the shipping and anchor, if the bottom and conditions allow.
• Continue into harbour only if you have a reliable radar, a well-practised blind pilotage plan, a channel with good marks and depth contours, and low traffic. Entering a busy commercial harbour in thick fog is usually the wrong choice.

Radar and blind pilotage

In fog, radar becomes your primary sensor for both collision avoidance and navigation.

• Use radar ranges and bearings of charted, radar-conspicuous objects to fix position.
• Use parallel indexing: draw on the radar a line parallel to your planned track at the charted distance off a headland or beacon. If the target slides along the line, you are on track.
• Plot or use ARPA/MARPA to determine CPA and TCPA of targets. Remember that small craft, wooden boats and buoys can disappear in sea clutter.
• Combine radar with GPS and depth: no single source should be trusted alone.

Fog signals

Sound the correct signal from your own vessel at intervals of not more than 2 minutes:

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A prolonged blast lasts 4 to 6 seconds, a short blast about 1 second. A vessel under 12 m that cannot carry the full equipment must still make some other efficient sound signal at intervals of not more than 2 minutes, so carry an aerosol or powered horn.

Navigation aids also have fog signals, listed in the almanac with their timing, for example "Horn(2) 30s" or "Siren Mo(N) 60s". Timing them can confirm identity, but sound is a poor guide to distance and direction: fog distorts it, there are silent zones, and it may not be heard at all. Never assume you are far from a fog signal because it sounds faint.

When you hear a fog signal apparently forward of the beam, Rule 19(e) requires you to reduce to bare steerage way, or stop, and navigate with extreme caution until the danger is over.

Blind Pilotage Step by Step

Blind pilotage means entering a harbour when you cannot see the marks, whether in fog, darkness or heavy rain. It is a Coastal Skipper skill and usually practised in daylight with the screen covered. Always have an alternative.

1. Decide whether to go in at all. Consider the traffic, the width of the channel, the tidal stream at the entrance, the depth at the time and the quality of the radar picture. A safer decision may be to stay out until the fog clears.
2. Choose waypoints. Select an approach waypoint in open water, 1 to 2 miles from the entrance, with a bearing and range from a charted radar target, and a series of leg waypoints to take you in.
3. Plan the cross-tide allowance. Calculate the course to steer for each leg, including the stream.
4. Pre-plan checks. For each leg write the course, distance, time, expected depth (corrected for tide), and the radar range and bearing to a charted object.
5. Execute with a team. One person steers, one monitors radar and calls ranges, one navigates and keeps the log, one keeps lookout and listens for fog signals. All are in lifejackets and clipped on.
6. Cross-check. Compare GPS, depth and radar every minute or two. If any disagree, slow down, stop or turn back.
7. Abort plan. Define in advance the point of no return and the abort criteria: depth below a limit, radar target not as expected, traffic ahead, loss of GPS, crew concern.

Worked example: cross-tide allowance

You are making a blind entrance with 2.0 miles to run to the entrance buoy at a boat speed of 4 knots. The tide is setting across your track at 1.5 knots from the port side.

• To hold your track you steer into the tide. The sine of the allowance angle is tide speed divided by boat speed: 1.5 / 4.0 = 0.375, so the angle is about 22 degrees.
• Speed made good along the track is about 4.0 x cosine of 22 = 3.7 knots.
• Time for 2.0 miles = 2.0 / 3.7 = 0.54 hours, about 32 minutes.
• If the track is 090 degrees True and the stream is setting you to the south (from the north, on the port side as you head east), you steer 090 minus 22 = 068 degrees True.

Without the allowance you would be set about 0.8 mile to the south of the entrance after 32 minutes, onto the very dangers you are trying to avoid.

Radar-assisted checks while blind

• Range ring and cursor: measure the range to a headland or a charted radar-conspicuous mark; plot the range ring on the chart.
• Parallel index (PI): a line on the radar screen parallel to your track and offset by the charted distance from a mark; if the mark slides along the line you are on track.
• Transit and guard zones: set a guard zone around your own vessel so that new echoes alarm.
• Do not trust the radar to see everything: small buoys, wooden boats and low shorelines may be missing, and rain or sea clutter can mask targets.

Watchkeeping, Fatigue and Safety at Night

• Watch systems. For a coastal passage with a crew of four, 3 hours on and 6 off is common for short passages; 4 on 4 off is the classic; for overnight passages a rotating "dog watch" prevents the same crew having the 0200 to 0500 slot repeatedly.
• Fatigue peaks between 0200 and 0500. Keep the most competent crew on watch, schedule difficult manoeuvres outside this window, and keep the log updated hourly.
• Handover brief. The outgoing watch leader gives the course, position, expected lights and traffic, sail plan and engine state, and the skipper's night orders. The oncoming leader repeats them back.
• Night orders are a standing instruction to call the skipper when: any vessel closes inside a given CPA (say 2 miles); the wind rises above a limit; the visibility drops below 2 miles; there is any doubt about position; and for any light that does not appear on time.
• Safety. Lifejackets with lights, and harnesses worn and clipped on from dusk (or before) when on deck. Use jackstays so you can reach any position from the cockpit without unclipping.
• Food and warmth. Hot drinks and food at regular intervals; keep hydrated; hypothermia and seasickness sap judgement and night vision.

Worked Example: Night Approach to Dartmouth

You are approaching Dartmouth at 2300 from the southwest, having rounded Start Point, in clear visibility, with a southwest wind force 4.

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5 miles out: You brief the crew: red lights only, lifejackets on, one lookout forward, the navigator below calling the plan. Instruments dimmed. The plan lists Start Point (Fl(3) W 10s, now astern, used for a last bearing), the Mewstone area, Castle Ledge buoy (Fl G 5s) and Kingswear Dir light (Iso WRG 3s) marking the entrance channel.

3 miles out: The navigator times a white light ahead: three cycles of 3 seconds with equal light and dark: isophase, matching Kingswear. A green flashing light every 5 seconds on the starboard bow is identified as Castle Ledge.

2 miles out: Steering to keep the Kingswear light white. It turns green: you are too far to starboard of the safe line. Alter to port until it shows white again, and hold the course on the charted bearing.

1 mile out: Castle Ledge is left to starboard. The sounder reads 12 m against a predicted 11.6 m (charted plus height of tide), confirming position. Speed reduced to 4 knots.

Entrance: the entrance marks are checked against the plan and the town lights are discounted; the lookout reports a fishing vessel's red over white and green sidelight coming out, bearing steady: you edge to starboard of the channel and slow until she passes.

Arrival: At minimum steerage speed, with the crew positioned with lines and fenders, you pick up the visitors' pontoon identified on the plan.

(Always use the current almanac for exact light characteristics; those above illustrate the method.)

Worked Example: Fog Closes In off Portland Bill

You are motoring at 5 knots, 6 miles south-west of Portland Bill, heading west, when fog reduces visibility to 100 m at 1400. High water is at 1630; the Portland Race and the Shambles lie to the north-east. Radar is working.

1. Fix. The navigator takes a fix from GPS and radar ranges and writes it in the log. Lifejackets and harnesses on, radar reflector already hoisted.
2. Safe speed. At 5 knots you cover 100 m in about 40 seconds. With the visibility at 100 m your own stopping distance of 10 to 15 m is acceptable, but a ship at 15 knots would cover 100 m in 13 seconds. You slow to 3 knots and keep the engine in gear ready for manoeuvre.
3. Fog signal. You sound one prolonged blast every 2 minutes (power-driven, making way).
4. Strategy. The shipping lane from Lyme Bay to the Channel passes through the area and the Portland Race is a hazard to the north-east. You decide to head north-west into shallower water and away from the main traffic, then anchor in 15 m with a bell signal if the fog persists.
5. Radar plot. A target appears at 2.5 miles, bearing 345 degrees relative, closing at a steady bearing. After 6 minutes it is at 1.7 miles on the same bearing: closing speed 8 knots; time to collision 13 minutes. You alter 60 degrees to starboard, slow to 2 knots, and the bearing begins to draw aft.
6. Hearing a signal. You hear two prolonged blasts forward of the beam: a power-driven vessel stopped. Rule 19(e) applies: reduce to minimum steerage speed and be ready to stop.
7. Anchoring. At anchor in 15 m with 45 m of cable out, you ring the bell rapidly for 5 seconds each minute. You switch on the anchor light, keep radar on guard and keep a lookout until the fog lifts at 1630.

Exam Tips: What the RYA Examiner Expects

• Plan before you leave. For a night entry the examiner expects a written pilotage plan, an abort plan, tidal heights and stream at arrival, and a crew brief.
• Name your lights. Describe the characteristics of each light and the time you expect to see it before you see it.
• Check against the chart. Say what you are verifying (bearing, depth, sector colour) every time you identify a mark.
• In fog, act at once: slow down, sound the signal, lifejackets on, radar on, lookouts posted. An examiner wants to see a calm, systematic response.
• Be honest about limits. A skipper who says "I will not enter in this visibility; I will stand off and wait" is safer than one who presses on.

Common Mistakes

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• Miscounting flashes or guessing the period. Use a stopwatch, count several cycles, and confirm the bearing.
• White light on deck or at the chart table. One flash ruins everyone's night vision for 20 minutes.
• Relying on a single source, usually the chartplotter. Cross-check with depth, bearings and radar.
• Keeping full speed in fog. Slow down before the fog arrives.
• No dedicated lookout. The helmsman cannot steer, navigate and watch the horizon.
• Not sounding fog signals. It is a legal requirement and may save your life.
• Confusing shore lights with navigation lights, especially red and green traffic lights, or a ship's deck lights for a lighthouse.
• Misjudging distance at night. Lights look closer than they are; a big ship's lights can be many miles off, a small craft's dim lights very close.

Summary

• Know light abbreviations and IALA Region A light codes; identify each light by timing, colour, bearing and expected position.
• Use sector light colour changes, leading lights and directional lights as precise position lines; use rising and dipping range for a fix.
• Protect night vision with red light, dim displays and off-centre scanning; allow 20 to 30 minutes for adaptation.
• Post a dedicated lookout and use a standard reporting format; use radar and AIS as aids, not replacements.
• Plan night pilotage thoroughly in advance, with lit marks, clearing lines, depth contours, a crew briefing and an abort plan.
• In fog, fix position early, prepare the boat, proceed at a safe speed, sound the correct signal, keep out of shipping, use radar and depth, and slow or stop when you hear a fog signal forward of the beam.

Check Your Understanding

1. What is the difference between flashing and occulting lights?

Answer: A flashing light has a total duration of light shorter than the dark; an occulting light has a total duration of light longer than the dark.

1. A light is 64 m above MHWS and your eye height is 2.25 m. At roughly what range will it rise above the horizon?

Answer: 2.08 x (8 + 1.5) = 2.08 x 9.5, about 19.8 miles, provided its nominal range and the visibility allow.

1. Approaching on leading lights, the rear (upper) light appears to the left of the front light. Which way do you alter?

Answer: To the left (towards the upper light). You are to the right of the leading line.

1. How long does full dark adaptation take, and how do you preserve it?

Answer: About 20 to 30 minutes. Use only dim red light, set displays to night mode at minimum brightness, avoid any white light, and allow the new watch time on deck before taking over.

1. How should you look at a faint light at night?

Answer: Slightly to one side of it, using peripheral (rod) vision, and scan slowly rather than staring directly.

1. You are motor-sailing in fog and making way. What signal do you sound, and at what interval?

Answer: One prolonged blast (4 to 6 seconds) at intervals of not more than 2 minutes, because you are a power-driven vessel making way.

1. Fog is forecast and you are 5 miles off a busy port. Give your preparations.

Answer: Fix position and log it; lifejackets on; navigation lights on; radar reflector or active enhancer working; engine running; radar and AIS on with guard zones; lookouts posted; fog signals ready; decide whether to stay in shallower water outside the shipping or wait at sea rather than enter the busy port.

1. Why is a fog signal a poor indicator of distance?

Answer: Fog distorts and attenuates sound unpredictably; there can be zones where a signal is not heard at all, and its apparent loudness does not reliably indicate range or direction.

1. What is a useful rule of thumb for safe speed in restricted visibility?

Answer: Be able to stop within half the distance you can see, adjusted for traffic, radar effectiveness and other Rule 6 factors.

1. A light is 30 m above MHWS. The height of tide is 2.0 m, MHWS is 5.0 m, eye height 3 m. What is the geographical range?

Answer: The effective height is 30 + (5.0 - 2.0) = 33 m. Range = 2.08 x (square root of 33 + square root of 3) = 2.08 x (5.74 + 1.73) = about 15.5 miles.

1. You must make good a track of 090 degrees True at 4 knots with a 1.5 knot stream setting you towards the south. Which course do you steer and what is your speed made good?

Answer: The sine of the allowance angle is 1.5 / 4 = 0.375, so about 22 degrees. You steer 068 degrees True, into the stream, and make good about 3.7 knots.

1. What are your night orders to the watch leader, and why are they written down?

Answer: A short written list of the criteria for calling the skipper: any vessel closing inside a set CPA, a change in weather or visibility, any doubt about position, an expected light not appearing. Writing them prevents misunderstandings at handover and ensures the skipper is called before a problem becomes an emergency.