Night Passage and Pilotage

Prerequisites

This lesson is part of the RYA Advanced Powerboat course, a two-day course that includes at least one exercise at night. You should already hold the RYA Intermediate Powerboat certificate, or be at that standard, which means you can plan and run a short daylight coastal passage, use a chart plotter and paper chart together, take a bearing, and work out a course to steer allowing for tidal stream. You should know the basic COLREGs lights for power-driven vessels and the IALA Region A lateral and cardinal marks. A VHF Short Range Certificate and a first aid certificate are strongly recommended for anyone skippering a fast boat, and both are assumed in other lessons on this course.

At night everything you learned in daylight still applies, but your information arrives in a different form: points of light instead of shapes, a glowing screen instead of a coastline. This lesson is about turning those lights back into a picture you can trust, and running the boat at a speed that matches what you can actually see.

Learning Objectives

By the end of this lesson you should be able to:

• Explain how the eye adapts to darkness and how to protect night vision on a powerboat.
• Identify vessels by their lights, including aspect (which way they are heading) and type.
• Read and recognise light characteristics from the chart and almanac, and time a light to confirm it.
• Explain why distance is hard to judge at night, and use rising and dipping range, radar and the plotter to judge it.
• Recognise back-lighting (background shore lights) and plan around it.
• Prepare a night pilotage plan, including light identification, clearing bearings, sector lights and leading lights.
• Choose a safe speed for the conditions, and brief the crew on clear night roles.

Why Night Is Different on a Fast Boat

A yacht at six knots gives you time to think. A powerboat at twenty-five knots covers a nautical mile in under two and a half minutes. At night three things combine against you:

1. You see less. Unlit objects, such as pot buoys, moorings, small unlit boats, logs and the edges of breakwaters, are invisible until very close.
2. You understand less of what you see. A light tells you there is something there, but not its size, its distance or, without care, what it is.
3. Your low eye height limits range. In an open RIB your eye might be only 1.5 to 2 metres above the water, so lights near sea level appear late.

The answer is not to avoid night passages, but to prepare more thoroughly than in daylight and to slow down. The RYA Advanced syllabus expects you to be able to run a passage at night with confidence, and that confidence comes from having identified every important light before you leave the berth.

Night Vision

How the eye adapts

The eye has two sorts of light sensors. Cones work in bright light and see colour and fine detail; they are concentrated in the centre of your vision. Rods work in dim light, see only shades of grey and are spread around the edge of the retina. When you move from bright light into darkness the rods take time to reach full sensitivity: most of the improvement happens in the first 10 minutes, and full dark adaptation takes 20 to 30 minutes.

A single glance at a bright white light (a torch, a phone screen, a white cabin light) can undo most of that adaptation in seconds. The rods then need many minutes to recover.

Protecting it

• Turn every instrument and plotter screen to night mode and dim it as far as you can while still reading it. Many plotters have a red or black night palette.
• Use red head torches and red chart lights. Red light affects the rods least. Even so, use the lowest brightness that works.
• Ban phones on deck unless they are in red mode and dimmed. A crew member checking messages destroys their own night vision and, if the screen faces the helm, yours too.
• If you must use white light (for example to inspect the engine or check a chart symbol), the person who does it should not be the lookout, and should turn away from the helm.
• Give a new lookout 10 to 20 minutes on deck before relying on them.

How to look

Because rods are not in the centre of the eye, a faint light can disappear when you look straight at it. Look slightly to one side of where you expect the light (averted vision) and sweep slowly across the horizon in sectors rather than staring at one spot. Keep the windscreen clean and dry: a salt-crusted or wet screen scatters light and turns every light into a smear. On many fast boats the best lookout position at night is standing, looking over the top of the screen, wearing clear protective glasses if spray is heavy.

Fatigue, cold and seasickness all reduce night vision. Keep the crew warm and fed, and rotate the lookout.

Recognising Vessels by Their Lights

The basic arcs

The COLREGs (Rules 21 to 23) define where each light can be seen. For a power-driven vessel under way:

The arcs fit together with no gap: 225 plus 135 is 360. So from any direction you see either a masthead light and at least one sidelight, or a sternlight alone.

The diagram below shows the arcs around a power-driven vessel and what an observer in each sector sees.

Click to zoom

Reading the aspect

• Red and green together, with white above: the vessel is heading straight at you. Both of you must alter to starboard (Rule 14).
• Green only, with white: you are looking at her starboard side. She is crossing from your port side to starboard, and if there is risk of collision you are the stand-on vessel (Rule 15), though you must still be ready to act (Rule 17).
• Red only, with white: you see her port side. She is crossing from your starboard side; you are the give-way vessel. Alter early and boldly, usually to starboard to pass astern of her.
• White only: you are probably looking at a sternlight, so you are astern of her. If you are closing, you are overtaking and must keep clear (Rule 13) whatever your relative positions afterwards.

Two masthead lights

A power-driven vessel of 50 metres or more must show a second masthead light, aft of and higher than the forward one. The pair gives you a superb indicator of heading: if the lights are in line, she is pointing at you or away from you; if the lower (forward) light is to the left of the higher one, she is heading to your left. Watch the pair over a minute or so. If the gap between them opens, she is turning away from you; if it closes, she is turning towards you.

Lights you will meet on the coast

Most of these also show sidelights and a sternlight when making way. If you see red or green above a white light, think "red over white, fishing at night", "green over white, trawling tonight" and "white over red, pilot ahead". Treat any vessel you cannot identify as needing a wide berth.

Range of visibility

Rule 22 sets the minimum ranges at which lights must be visible:

The lesson for a fast boat: the sidelights of another small craft may not be visible until a mile away. Two boats closing head-on at 25 knots each cover that mile in 72 seconds. Your own lights are equally weak, so do not assume others have seen you.

Your own lights

Check your navigation lights before dark, and carry spare bulbs or a spare portable light set. On many RIBs the all-round white is on a pole that can be hidden by people standing in the boat or by the console canopy; check it from outside the boat. Do not run with deck lights or a white work light on: they ruin your own night vision and can hide your navigation lights from other vessels.

Light Characteristics

Navigation marks and lighthouses each have a characteristic: a colour, a pattern of flashes and a period. The chart gives it in abbreviated form, for example Fl(2)R.10s, which reads as group flashing two, red, repeating every 10 seconds.

The period is the time for one complete cycle, from the start of one pattern to the start of the next. It is the most reliable thing to check, because flash patterns can be confused when a light is faint or partly hidden by waves.

The timing chart below shows several common characteristics over 10 seconds.

Click to zoom

Characteristics of IALA Region A marks

For cardinals, think of a clock face: three flashes for east (3 o'clock), six for south, nine for west. The long flash after the six south flashes stops it being mistaken for the three of east or the nine of west when a flash is missed.

Timing a light

When a light appears, time it before you name it. Count aloud, or use a stopwatch, over at least three cycles: "flash, flash ... and one and two and three ...". A crew member can call the time from a watch with a dim red display. Compare the result with the chart and your pre-written light list. If it does not match, do not "make it fit". Assume you have not identified it and keep looking.

At a fast boat's low eye height, waves can hide a light for a second or two, so a Fl(3) can briefly look like a Fl(2). Timing over several cycles cures this.

Judging Distance at Night

Why it is hard

At night you lose the clues you use in daylight: the size of the object, the detail you can see, the colour of the water near it. A bright light far away and a dim light close by can look the same. Lights often seem closer than they are, and a moving vessel's speed is very hard to judge. A cluster of lights from a large ship can look like a small boat until you are much too close.

Rising and dipping distance

A light first appears over the horizon (it "rises") at a range that depends on its height and on your eye height. Its geographical range, in nautical miles, is roughly:

range = 2.08 x (square root of light height in metres + square root of eye height in metres)

Worked example: a lighthouse 49 metres above sea level, seen from a RIB with your eye 2 metres above the water.

• Square root of 49 is 7.0.
• Square root of 2 is about 1.4.
• 2.08 x (7.0 + 1.4) = 2.08 x 8.4 = about 17.5 nm.

If the light's nominal range (its brightness range in clear weather, printed on the chart) is greater than this, the light will appear over the horizon at about 17.5 nm. When it first appears, take a bearing: a bearing plus a rising distance gives you a rough position. If the light's nominal range is less than the geographical range, you will see it only when it comes within its brightness range, and the method does not work. If you stand up, the range increases a little; if you crouch, it may disappear (it "dips"), which confirms you are at the edge of its range.

Admiralty List of Lights and almanacs give the elevation; nominal range is on the chart, for example Fl.10s 49m 22M.

Other ways to judge range

• Radar: the variable range marker gives a direct range to an echo. This is the best method, but you must link the echo to the light correctly.
• Plotter: if you have identified the light, the plotter gives the distance from your position to the charted mark.
• Bearing change: a light whose bearing moves quickly across your bow is close; a distant light moves slowly.
• Detail: if you can see the structure of a mark, the shape of a buoy or the outline of a ship's hull, you are close.

Back-Lighting

The single biggest problem on the UK coast at night is not darkness but too much light. Harbours, towns, roads, piers and floodlit docks make a bright background in which a small flashing red buoy simply disappears. This is called back-lighting.

The diagram below shows the effect: a harbour entrance buoy against a town front, and how a careful pilotage plan avoids relying on it.

Click to zoom

How to deal with it

• Before you leave, study the area on a large-scale chart and in the pilot book or almanac. Note which lights are likely to be lost against the shore.
• Use characteristics that stand out: a flashing light is easier to find among steady shore lights than a fixed light. Look for the rhythm, not the brightness.
• Use bearings. Work out from the chart the bearing on which a buoy should lie from a known point, then look along that bearing with the hand-bearing compass.
• Use the plotter and radar to tell you where to look, but confirm with your eyes. A buoy may be off station, and moored boats near a channel are unlit.
• Approach slowly. Back-lit entrances are where most night collisions with buoys and moorings happen.
• Watch for lights moving against the background. A vessel crossing in front of a town will show as a small light whose bearing changes against fixed shore lights.

Planning Night Pilotage

Principles

Pilotage is navigation by eye using marks, bearings and transits, with no time to plot. At night the same applies, but you navigate by lights and by bearings to lights. A good night plan:

1. Breaks the route into short legs, each with a heading and a distance.
2. Names the light (with characteristic) you steer for, or keep on a bearing, on each leg.
3. Gives a clear signal for each turn: a bearing on a light, a buoy abeam, a transit opening, or a depth contour.
4. Lists clearing bearings that keep you off dangers.
5. Notes unlit dangers: moorings, unlit marks, rocks, pot fields, unlit posts.
6. States what you will do if you lose a light or become unsure: stop, hold position, check the plotter.

Write the plan on a card or in a waterproof notebook, in large clear writing, and keep it where the navigator can read it by red light. Do not rely on a phone in your hand.

Sector lights and leading lights

Many harbours have directional or sector lights. A sector light shows different colours on different bearings. Typically a narrow white sector marks the safe approach, with red and green sectors either side. In the UK the red sector is usually on the port side of the approach and green on the starboard side, matching the lateral marks, but always check the chart, because there is no rule that requires it. If you see white, you are in the safe channel; if it turns red or green, you have drifted off line and should steer back towards the white.

Leading lights are two lights, one higher and behind the other. When they are vertically in line you are on the leading line. If the upper (rear) light moves to the left of the lower one, you are to the right of the line, so steer left, back towards it ("follow the top light").

The chartlet below shows a simple night pilotage plan for a harbour approach using a sector light, two lateral buoys and a clearing bearing.

Click to zoom

Clearing bearings at night

A clearing bearing is a bearing on a fixed light that keeps you clear of a danger. For example: "Keep the lighthouse bearing more than 045 degrees to stay clear of the ledge." At night choose clearing lines on lights you are certain of, and remember that sectors on lighthouses often show red over dangers. The red sector of a lighthouse is itself a clearing line: if you see red, you are over or near the danger.

Using the plotter

A plotter makes night pilotage much easier but it is not a substitute for the plan:

• Set the plotter to a large scale for the pilotage area and check that the chart is up to date.
• Enter waypoints at turning points, but place them clear of buoys, never on them, or you will steer straight for the mark.
• Set the depth and cross-track alarms.
• Check the plotter's picture against what you see. If the plotter says a red buoy should be fine on the port bow and you cannot see it, slow down until you can.

Choosing Your Speed

Rule 6 of the COLREGs requires every vessel to proceed at a safe speed at all times, so that she can take proper and effective action to avoid collision and be stopped within a distance appropriate to the conditions. At night the factors listed in Rule 6 include "the presence of background light such as from shore lights or from back scatter of her own lights".

A practical approach:

• Open water, clear night, good visibility, little traffic: a planing speed can be safe, but well below your daytime cruising speed. If you cannot see the water surface 50 metres ahead, you will not see a pot buoy or a log in time at 25 knots.
• Coastal water with fishing gear, moorings or small craft: reduce to a speed at which you could stop or turn away from an unlit object within the distance you can actually see it. Often this is a slow plane or displacement speed.
• Harbours, rivers and back-lit approaches: displacement speed. Obey speed limits, which still apply at night.

Remember that a boat coming off the plane drops into its own wake and may pitch the bow up, hiding the view ahead for a moment. Slow down gradually, in good time.

Night is also when speed perception fails. With no visual reference the boat seems slower than it is, so watch the speed over ground and keep checking the time against your plan.

Crew Roles at Night

On a small boat everyone has a job, and at night each job must be clear before you leave the berth.

On a two-person crew the skipper is usually navigator and lookout while the other person helms. In that case the navigator should spend short periods heads-down, call "heads down" before doing so, and keep the helm briefed.

The night briefing

Before departure brief:

• The route, the main lights to expect and their characteristics.
• What each person does, and the standard words for reports.
• The rules on white light and phones.
• Lifejackets on and fastened, with lights and crotch straps; a personal light for everyone. A casualty in the water at night is very hard to find without a light.
• Where the MOB equipment and the search light are, and the MOB drill at night: shout, point, press the MOB button, keep a searchlight beam on the casualty.
• When you will review progress: at each waypoint, or every 15 minutes.

Calling lights

A standard way of reporting reduces confusion: position relative to the bow, colour, then rhythm. "White light, two points on the port bow, flashing every five seconds." The navigator then times it, checks it against the plan and confirms: "That is the Fl.5s on the breakwater head."

Worked Example

You are skipper of a 7.5-metre RIB with twin outboards, returning at night from a day trip. The final 6 nm run is from a headland to a harbour with a sector light behind the entrance: Oc.WRG.6s, white sector 355 to 005 degrees true, red to the west, green to the east. The entrance is marked by a port-hand buoy Fl.R.4s and a starboard-hand buoy Fl.G.4s. A rocky ledge lies 1 nm south-west of the entrance, with an east cardinal mark, Q(3)10s, on its eastern side. The town behind the harbour is bright.

Planning before departure

1. You list the lights: headland lighthouse Fl(3)15s, ledge east cardinal Q(3)10s, sector light Oc.WRG.6s, entrance buoys Fl.R.4s and Fl.G.4s.
2. You note that the entrance buoys will be back-lit by the town, and that there is a mooring field to the east of the entrance, unlit.
3. Legs: leg 1, headland to a waypoint 2 nm south of the entrance, 5 nm at 20 knots, 15 minutes. Leg 2, 000 degrees true in the white sector, 2 nm at 8 knots, 15 minutes. Leg 3, between the entrance buoys at 5 knots.
4. Clearing line: keep the sector light white or green on leg 2, never red, which would put you over towards the ledge. A second check: the east cardinal marks the safe side, so pass east of it, keeping it on your port side.

On passage

• On leg 1 the navigator picks up the headland light astern and times it: three flashes every 15 seconds. Confirmed.
• Approaching the waypoint, a white light appears ahead. The navigator times it: occulting, 6 seconds. It is white, so you are in the white sector. You turn onto 000 degrees and slow to 8 knots.
• Halfway in, the light turns green. You have drifted east (the green sector is on the starboard side of the approach). You steer a few degrees left until it shows white again.
• At 0.5 nm the buoys are lost against the town lights. The navigator uses the plotter and the hand-bearing compass along 000 degrees to look for flashing lights with a 4-second period, and finds both. You slow to 5 knots and pass between them, keeping clear of the moorings to starboard.

Common Mistakes

• Destroying night vision. A white torch or bright plotter undoes 20 minutes of adaptation. Use red light and night modes.
• Naming a light before timing it. Under pressure people see what they expect. Time over three cycles and compare with the written list.
• Too fast for what you can see. Unlit pots, logs and moored boats cause many night accidents. Match speed to the distance you can actually see.
• Relying on the plotter alone. Waypoints placed on buoys, out-of-date charts and position errors all mislead. Use the plotter to tell you where to look, then look.
• Forgetting back-lighting. Plan how you will find marks against bright shore lights before you get there.
• No plan for losing a light. If you lose your reference, slow down or stop and re-establish your position. Never press on hoping.
• Poor crew briefing. If no one knows who is lookout, no one is.
• Forgetting astern. Faster boats, including other RIBs and patrol craft, may overtake you; their lights are easy to miss behind you.

Summary

• Full night vision takes 20 to 30 minutes and is lost in seconds. Use red light, dim screens and averted vision.
• Masthead 225 degrees, sidelights 112.5 degrees each, sternlight 135 degrees. Read aspect from the sidelights and, on ships of 50 metres or more, from the two masthead lights.
• Know the common day and night signals for fishing, trawling, towing, restricted manoeuvrability, not under command and pilot vessels.
• Light characteristics give colour, rhythm and period. Time every light over several cycles and check it against a written list.
• Distance is hard to judge at night; use radar, plotter, rising range and bearing change.
• Back-lighting hides marks; use bearings, rhythm and slow speed to find them.
• A night pilotage plan has short legs, named lights, clear turning signals, clearing bearings and a plan for losing a light.
• Safe speed at night is the speed at which you could stop or turn for something you can only just see. Slow right down near harbours.
• Brief the crew on roles: skipper, helm, navigator and lookout, with standard reports.

Check Your Understanding

1. How long does full dark adaptation take, and what is the best light to use on deck at night?

Answer: About 20 to 30 minutes, with most of the improvement in the first 10. Use dim red light, since it affects the rods least, and keep screens on their night setting.

1. You see a white light with a red light below and to its right, and no green. What are you looking at and what should you do?

Answer: A power-driven vessel's port sidelight and masthead light. She is crossing from your starboard side, or showing you her port side, so if there is risk of collision you are the give-way vessel. Alter early and boldly, normally to starboard to pass astern of her.

1. A ship shows two white masthead lights. The lower light is to the right of the upper one and the gap is closing. What does this tell you?

Answer: The lower (forward) light being to the right means her bow points to your right. The gap closing means she is turning towards you, so her heading is coming round to point at you. Watch closely and be ready to act.

1. What is the characteristic of a south cardinal mark, and why does it have a long flash?

Answer: Q(6)+LFl 15s (or VQ(6)+LFl 10s). The long flash after the six quick flashes stops it being mistaken for an east (three) or west (nine) cardinal when a flash or two is missed or hidden by waves.

1. A light 36 metres high is seen from a RIB with eye height 2.25 metres. At about what range will it first appear, assuming its nominal range is greater?

Answer: 2.08 x (square root of 36 + square root of 2.25) = 2.08 x (6 + 1.5) = 2.08 x 7.5 = about 15.6 nm.

1. What is back-lighting and give two ways to deal with it?

Answer: Navigation lights being lost against a bright background of shore lights. Ways to deal with it include: identify in advance which marks will be affected, look for the flash rhythm rather than brightness, use the hand-bearing compass along the charted bearing, use plotter and radar to know where to look, and slow down.

1. You are approaching a harbour in the white sector of a sector light and it turns red. In this harbour red is on the port side of the approach. What do you do?

Answer: You have drifted to port (off line towards the red side), so steer to starboard until the light shows white again, slowing if needed.

1. Give three things a night pilotage plan should include.

Answer: Any three of: short legs with headings and distances, the lights (with characteristics) for each leg, a clear signal for each turn, clearing bearings, unlit dangers such as moorings and pot fields, and the action to take if you lose a light or become unsure of position.

1. What does Rule 6 say about safe speed at night that is especially relevant near towns?

Answer: Among the factors to consider, Rule 6 lists the presence of background light, such as from shore lights or from back scatter of your own lights. Safe speed must allow you to stop or take effective action within the distance you can see.

Further Reading

• RYA Advanced Powerboat Handbook G108
• RYA Powerboat Handbook G13
• RYA Powerboat Scheme Syllabus and Logbook G20, and the Advanced course summary
• RYA Navigation Handbook G6 (Sara Hopkinson)
• MSN 1781 (M+F) Amendment 3, COLREGs as UK law
• Dag Pike, Fast Boat Navigation (Adlard Coles), with Reeds Nautical Almanac for pilotage data
• A.N. Cockcroft and J.N.F. Lameijer, A Guide to the Collision Avoidance Rules