Lesson 7 of 13 · Module 2 — Finding your way

Lights at night

Light characteristics, what a harbour looks like after dark, why charter companies say arrive by daylight, and your own yacht's lights.

Day Skipper18 minVideo · Notes · Interactive · Exercises

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0:00 / 5:11Chapter 1 of 9: Lights in the dark

Transcript

At night the coastline disappears, and lights take over. Every lighthouse, beacon and lit buoy shows its own pattern of light and dark, called its characteristic. Out there: three flashes, then darkness, every ten seconds. That pattern says Gull Point lighthouse, on our practice chart of the Isle of Kerran. In this lesson you will learn to read a light on the chart, find it among the lights of a harbour, and show the right lights on your own yacht. You will also see why charter companies want you tied up before dark.
On the chart, a light is marked with a magenta flare, shaped like a teardrop. A lighthouse is drawn as a star with the flare beside it, and its characteristic is printed alongside. Lit buoys have a flare too, usually with just the rhythm, the colour and the period, like the red and green buoys into Port Kerran. On most plotters you can tap a light to see its characteristic written out in full.
Every characteristic is written in the same order. First comes the rhythm: Fl(3) means group flashing, three flashes at a time. Next comes the colour, and here there is no letter, which means white. Then the period, 10s, the time for one whole cycle from the start of one group to the start of the next. Last come the height of the light, 28m, and how far it can be seen on a clear night, 15M.
The charted range is for a clear night, and real nights are rarely that kind. Haze, rain and the glare of a town all cut it down, so a light may appear much later than you expect. Buoy lights are small and low, and you will often pick them out only in the last mile or two. The curve of the Earth hides a low light too, which is why the big lighthouses stand tall. So never name a light from one glance: check its colour, its count and its period first.
Here are the rhythms you will meet most often. Fl is flashing: short flashes, with more dark than light. Fl(3) is group flashing, with a longer darkness between the groups. Q is quick, about one flash a second, and VQ is very quick, about two a second. Iso is isophase, with equal light and dark. Oc is occulting, the opposite of flashing: mostly on, blinking off once each period.
To identify a light, first note its colour. Then count the flashes in each group. Then time the period with the stopwatch on your phone, from the first flash of one group to the first flash of the next. Time several periods and divide, and the answer is better still. White, two flashes every five seconds: on our chart, that can only be Mew Rock beacon.
Here is the view ahead as you come into Port Kerran at night. The town behind the harbour is a carpet of lights: streets, bars, cars and windows. The navigation lights hide among them, and the trick is that shore lights are steady while navigation lights keep a rhythm. The two leading lights blink out together, one above the other, and the red and green buoys flash low on the water. Red lights high on the hill are not buoys at all, but the warning lights on a radio mast. Even when you have named every light, distance is hard to judge in the dark, and a moored boat or the end of a quay can appear very suddenly.
This is why most charter companies ask you to be in harbour or at anchor before dark. Many charter contracts forbid sailing at night altogether, and breaking the rule can leave you without insurance cover. Plenty of hazards carry no light at all: rocks, mooring buoys, fish farm cages, swimming area floats and unlit small boats. In the Caribbean many reefs are unmarked, and near the equator, in the Seychelles or Phuket, night falls fast at about the same time all year. So plan to arrive by mid-afternoon, with a couple of hours in hand if the wind dies or the anchor will not hold. If you are caught out, slow right down, put your lights on, and head for the simplest, best-lit entrance you can reach.
Your yacht must show navigation lights from sunset to sunrise, and in poor visibility. Under sail you show red to port, green to starboard and white astern. Many yachts can show all three from one tricolour lantern at the top of the mast, but only under sail. With the engine running, even with the sails up, you count as a motor boat: use the deck-level lights and add the white steaming light on the front of the mast. At anchor, switch the navigation lights off and show one white light that is visible all round, usually at the masthead. Check every light at handover, because a blown bulb is easier to fix on the pontoon than at sea.

In this lesson you will learn

Read a light’s characteristic on the chart: rhythm, colour, period, height and range
Identify a light at night by its colour, count and period, and pick navigation lights out from shore lights
Explain why charter companies say arrive by daylight, and plan a day that does
Show the right lights on your own yacht under sail, under engine and at anchor

Lights on the chart

By day you recognise a mark by its shape and colour. At night those disappear, so every lighthouse, beacon and lit buoy shows its own pattern of light and darkness, its characteristic, and the chart tells you what to look for. Learn to read it, and a dark coast full of winking lights turns into a map you can steer by.

On a paper chart a light is marked with a magenta flare, a small teardrop. A lighthouse is drawn as a star with the flare beside it, and its characteristic is printed alongside in a compact code. Gull Point lighthouse, at the eastern end of our practice island, is printed Fl(3)10s28m15M.

Gull Point lighthouse on the practice chart: a star, a magenta flare and its characteristic, with the lit buoys off The Teeth to its east.

Lit buoys carry a flare too, with a shorter characteristic: just the rhythm, colour and period, such as Fl G 5s on No 1 buoy at the entrance to Port Kerran. Their lights are small and low, and the chart gives no height or range for them. On most chart plotters and charting apps you can tap or hover over a light to see the same characteristic written out in full, which is handy when the screen is too cluttered to read.

Reading a characteristic

Every characteristic is written in the same order. Learn the order and you can read any light:

Fl(3) 10s 28m 15M

rhythm (and group) · colour · period · height · range

Part	Gull Point	What it means
Rhythm	Fl(3)	Group flashing: flashes in groups of 3
Colour	none	No letter means white. Otherwise R red, G green, Y yellow
Period	10s	One complete cycle takes 10 seconds, from the start of one group to the start of the next
Height	28m	The light is 28 metres above high water (small m: metres)
Range	15M	Seen up to about 15 nautical miles on a clear night (capital M: miles)

Spacing and dots vary between charts, books and plotters (Fl(3)10s28m15M, Fl(3) 10s 28m 15M or Fl.(3)10s), but the order never changes.

InteractiveCharacteristic decoder

Pick a light from the practice chart, or type any characteristic, and watch it flash with every part explained.

On the practice chart

More examples

Or type a characteristic, in chart order

Capitals matter: Fl, LFl, Q, VQ, Iso, Oc, Mo — and M for miles, m for metres.

white, group flashing, 3 flashes every 10 seconds, 28 m above MHWS, range 15 miles0.0 s of 10 s

Fl(3)Rhythm. Group flashing: 3 flashes in each group.
noneColour. No letter, so the light is white (charts usually leave W out).
10sPeriod. One complete cycle takes 10 seconds, from the start of one group to the start of the next.
28mElevation. The light is 28 m above MHWS.
15MNominal range. 15 M: how far it can be seen on a clear night.

Light for about 15% of each period: less light than dark. On the practice chart: Gull Point lighthouse.

The rhythms you will meet

Written	Name	What you see	Typical use
F	Fixed	A steady light that never goes out	Some harbour lights; easy to confuse with shore lights
Fl 5s	Flashing	Single short flashes, more dark than light	Lighthouses, lateral buoys
Fl(3) 10s	Group flashing	Flashes in groups, with a longer dark gap between	Lighthouses, lateral buoys such as Fl(2) R
LFl 10s	Long flashing	One flash of two seconds or more	Safe water marks
Q	Quick	About one flash a second, without a break	North cardinal marks
VQ	Very quick	About two flashes a second	Cardinal marks, new dangers
Q(3) 10s	Group quick	Quick flashes in groups	East, south and west cardinal marks
Iso 4s	Isophase	Equal light and dark	Lighthouses, leading and safe water lights
Oc 4s	Occulting	Mostly on, blinking out	Leading lights, harbour lights

For any light ask one question first: is it on for less time than it is dark (flashing), the same (isophase), or more (occulting)?

InteractiveEvery rhythm side by side

Each strip shows the last ten seconds of a light, so the rhythms compare directly.

FFixed

Steady, never goes out

Fl 5sFlashing

Light shorter than dark

LFl 10sLong flashing

One flash of 2 s or more

Fl(3) 10sGroup flashing

Flashes in groups

QQuick

50 to 79 a minute

VQVery quick

80 to 159 a minute

Q(3) 10sGroup quick

Quick flashes in groups

Iso 4sIsophase

Equal light and dark

Oc 4sOcculting

Light longer than dark

Oc(2) 8sGroup occulting

Eclipses in groups

Mo(A) 6sMorse code

A: short, long

Al WRAlternating

Changes colour

Each strip shows the last 10 seconds, ticked every second; its right-hand end is now. Timings are representative: real lights vary, but the pattern and the period are what you look for.

What you really see

The range on the chart is how far the light can be seen on a clear night. Real nights are rarely that clear. Summer haze in the Mediterranean, rain, sea spray, and above all the glare of a lit town all cut it down, so a light often appears much later than the range suggests. Do not worry if a fifteen-mile light is not in sight at twelve miles; do worry if it is still missing when you are close.

Buoy lights are small and low. Expect to pick them out only in the last mile or two, often against a bright background.
The curve of the Earth hides low lights. That is why major lighthouses stand high on headlands: their light clears the horizon from further away.
A light does not label itself. Check the colour, the count and the period before you name it, and check what you name against the chart or plotter.

Identifying a light

Colour. White, red, green or yellow.
Count. How many flashes in each group, or is it steady, quick, equal or mostly on?
Period. Time it with the stopwatch on your phone, from the first flash of one group to the first flash of the next. Time several periods and divide.
Check. Find the light on the chart or plotter with that characteristic, near where you think you are.

Worked example

Which light is that?

1South of Kerran at night you see a white light giving two flashes, then darkness.
2You start the stopwatch at the first flash of one pair and stop it at the first flash of the fourth pair: 15.2 seconds.
3That is three periods, not four: 15.2 ÷ 3 = 5.07, so the period is 5 seconds.
4White, two flashes, 5 seconds: Fl(2) 5s. No 3 and No 4 buoys share the rhythm but are green and red.

Mew Rock beacon, Fl(2)5s: an isolated danger mark. Keep clear of the rock under it.

InteractiveNight trainer

A light from the practice chart is flashing. Time it with the stopwatch, then choose which light it is.

0.0 s

Each lap is one period. For a light that is mostly on, time from one eclipse to the next. Timings are representative.

Which light on the practice chart is it?

A harbour after dark

From seaward, a harbour town at night is a carpet of lights: street lamps, bars, cars on the waterfront, windows, the anchor lights of boats in the bay. The navigation lights are in there somewhere, and at a big waterfront such as Palma or Split they can be very hard to pick out. The trick is rhythm: shore lights are steady, while navigation lights flash, occult or keep an equal beat. Look low on the water for the buoys, and for pairs of lights in line, one above the other, for leading lights.

At Port Kerran the leading lights are Oc 4s: white, mostly on, blinking out together. The inner buoys flash in pairs, Fl(2) G 5s and Fl(2) R 5s. Above the town, two steady red lights are the warning lights on the radio mast, not buoys: a buoy can never be high on a hill.

InteractiveFind the lights among the town

You are between No 1 and No 2 buoys, looking up the channel. Tap the lights each task asks for.

1 of 3Tap the two Port Kerran leading lights (Oc 4s).

Heights are exaggerated so the lights are easy to tap. Timings are representative.

Why charter companies say arrive by daylight

Most charter companies ask you to be in harbour or at anchor before dark, and many bareboat contracts forbid sailing at night altogether. Read yours at check-in: breaking the rule can leave you without insurance cover, and at the very least it is a hard conversation if something goes wrong. The reasons are good ones:

Plenty of hazards carry no light. Rocks, mooring buoys, fish farm cages (common in Croatia, Greece and Turkey), swimming area floats, unlit small boats and fishing-net floats.
Charter crews are new to the boat and the coast. Night is not the time to learn where the switches are, or what the pilot book meant by a shallow patch.
Anchoring and berthing are harder. You cannot see the seabed, the colour of the water or the lines of the boats either side.
In the Caribbean many reefs are unmarked, and in the BVI, for example, charter companies forbid sailing after dark. Near the equator, in the Seychelles or Phuket, the sun sets at roughly the same time all year and dusk is short.

Sunset moves a lot through the Mediterranean season: in Croatia in midsummer the sun sets after eight in the evening, but by late October, once the clocks go back, it is down before five. Plan the day so you arrive by mid-afternoon, with a couple of hours in hand for a dying wind, a full harbour or an anchor that will not hold.

InteractiveWill we be in before dark?

Enter the day’s distance, your average speed, when you leave and the sunset time.

Distance (miles)Average speed (knots)Leave atSunset

Good: in with daylight to spare.

18 miles at 5.5 knots takes about 3 h 16 min, so you arrive about 13:46, 5 h 54 min before sunset.

Two hours in hand covers a dying wind, a slow anchoring or a full harbour. Check the sunset time for your date and place in a weather app or on the plotter: near the equator, in the Seychelles or Phuket, it changes little through the year and dusk is short.

Your own yacht’s lights

From sunset to sunrise, and in poor visibility by day, your yacht must show the right navigation lights. Each light covers a set arc, so another boat can tell from your lights which way you are heading.

The arcs of a vessel’s lights, from above: green to starboard and red to port, each from right ahead to just behind the beam; a white sternlight over the rest; and, when the engine is on, the white steaming (masthead) light forward.

What you are doing	Lights to show	Switch panel
Sailing, engine off	Red and green sidelights and a white sternlight; or, instead, a tricolour at the masthead	Nav lights, or Tricolour
Motoring, or motor-sailing with sails up	Sidelights, sternlight and the white steaming light on the front of the mast. Never the tricolour	Nav lights and Steaming
At anchor	One all-round white light, where it can best be seen (usually the masthead)	Anchor

InteractiveSee your yacht as others see her

Choose what your yacht is doing and where the other boat is, and see which of your lights they can see.

Under sail alone: red sidelight to port, green to starboard, white sternlight. No white light on the mast.

From above: where each light can be seen

What a boat on your starboard bow sees: her green sidelight.

The other boat is on your:

Light timings in this lesson are representative; the pattern and the period are what you look for. This course is independent training material by Nautical Nomads and is not accredited by the RYA or any other body.

Key terms

Characteristic: A light’s pattern of colour, rhythm and period, printed on the chart beside its magenta flare.
Period: The time for one complete cycle of a light, from the start of one group to the start of the next.
Flashing (Fl): Flashes shorter than the darkness between them; Fl(3) is group flashing, three at a time.
Quick (Q): About one flash a second; very quick (VQ) is about two a second.
Isophase (Iso): Equal periods of light and darkness.
Occulting (Oc): On for longer than it is off: a light that blinks out.
Range: How far a light can be seen on a clear night, in nautical miles (the capital M).
Tricolour: One lantern at the masthead showing red, green and white sectors; for use under sail only.
Steaming light: The white masthead light shown forward when a yacht is under engine, with her sails up or not.
Anchor light: An all-round white light shown by a vessel at anchor, from sunset to sunrise.

Exercises

Check your understanding. You get a second try at each question, then the worked answer. Score 70% or more to complete the lesson; your progress is saved in this browser.

Read Gull Point lighthouse’s characteristic on the chart. What is the period of its light, in seconds?

Read Kerran Head light’s characteristic on the chart. How high is the light, in metres?

Mew Rock beacon is charted Fl(2)5s. What colour is its light?

Gull Point is Fl(3)10s28m15M. What does the 15M at the end tell you?

Which of these lights is on for LONGER than it is dark in each period?

At night you see a white light with equal periods of light and darkness: two seconds on, two seconds off. Tap that light on the practice chart.

You see a red light: two flashes, then darkness, the pattern starting again every five seconds. How would the chart print it?

Approaching a harbour at night, you see two red lights, one above the other, high above the town. They never go out. What are they most likely to be?

A harbour town is ablaze with lights. What is the best way to pick out the navigation lights among them?

At 15:30 the wind dies. You are 15 miles from tonight’s marina, motoring at 5 knots, and sunset is at 18:20. The contract says no sailing at night. What is the best plan?

At dusk you are motor-sailing: main up, engine running. Which lights should you show?

You are spending the night at anchor in a bay. Which light do you show?

0 of 12 answered · 0 correct

Decode the light

Five fresh questions each time: periods, groups, colours and rhythms of randomly built lights, the practice chart’s lights, and your own yacht’s lights.