The skipper makes the weather decisions, but the whole crew lives with them. Know how wind is named and measured, what a forecast is telling you, and which signs in the sky and on the barometer deserve a word to the skipper.
Does a northerly wind blow from the north or towards the north?
From the north: wind direction is always named after where the wind blows from. A flag streams downwind, so one streaming towards the south-east shows a north-westerly.
Wind is always named after the direction it blows from. A northerly blows from the north towards the south; a sea breeze blows in from the sea.
Flags, smoke and boats at anchor show the wind the other way round: a flag streams downwind. If it streams towards the south-east, the wind is a north-westerly.
How many knots is Force 5 on the Beaufort scale?
17 to 21 knots, a fresh breeze with many white horses: time to reef. On the Beaufort scale Force 4 is 11–16 knots, Force 6 is 22–27, and Force 8, a gale, is 34–40.
Forecasts give the wind as a Force on the Beaufort scale. Each Force is a band of wind speeds in knots, and the sea grows with it.
| Force | Knots | Name | On a yacht |
|---|---|---|---|
| 3 | 7–10 | Gentle breeze | Easy sailing under full sail |
| 4 | 11–16 | Moderate breeze | Good sailing, some white horses |
| 5 | 17–21 | Fresh breeze | Many white horses, time to reef |
| 6 | 22–27 | Strong breeze | Reefs, spray, lifejackets on |
| 7 | 28–33 | Near gale | Hard going for boat and crew |
| 8 | 34–40 | Gale | Stay in port |
Force 4: a good sailing day. Force 6: hard work. Force 8: a gale.
What does "N 3 to 4, increasing 5 later" mean in a sailing forecast?
A northerly Force 3 to 4 now, building to Force 5 later in the day: words of change such as increasing, becoming and later describe the rest of the day, not just the morning.
A marine forecast keeps to one order: wind direction and Force, the state of the sea, the weather, the visibility. Listen for the words of change: increasing, becoming, later. They describe the rest of the day, not just the morning.
| Visibility | You can see |
|---|---|
| Good | More than 5 miles |
| Moderate | 2 to 5 miles |
| Poor | Less than 2 miles |
| Fog | Less than 1,000 metres |
What time does the sea breeze start, and when does it die?
Around midday: on a hot, settled day the sea breeze fills in about noon, is strongest in mid-afternoon and dies at sunset. At night a light land breeze drifts offshore until morning.
On a hot, settled day the land heats up faster than the sea. Warm air rises over the land and cooler air flows in from the sea to replace it: the sea breeze. It fills in around midday, is strongest in mid-afternoon and dies at sunset.
A calm morning anchorage close off a beach can have the wind blowing onto that beach by three o'clock. At night it reverses: the land cools faster than the sea, and a light land breeze drifts offshore until morning.
What time of day is the Meltemi strongest in the Aegean?
In the afternoon: the Meltemi, the Aegean's summer northerly, often blows Force 5 to 7 for days, usually eases overnight and builds through the day. That is why crews in the Cyclades sail early.
The Meltemi is the summer wind of the Aegean. It blows from the north under clear skies, often Force 5 to 7 for days on end. It usually eases overnight and builds through the day to its strongest in the afternoon. So crews in the Cyclades make their passages early, and any leg towards the north is a beat into wind and waves.
Land bends any wind and speeds it up. It funnels through gaps between islands and round headlands, where it blows harder than in open water. In the lee of high land the water may look calm, but the wind that has climbed over the top falls down the slope in sudden, violent gusts.
How fast does the barometer have to fall to warn of strong wind?
A fall of several hPa in three hours warns of strong wind: on the barometer the change matters more than the number. Steady or slowly rising pressure means settled weather.
The barometer shows air pressure in hectopascals (hPa). The number itself matters less than the change, which is why it is logged every few hours. Steady or slowly rising pressure means settled weather. A fall of several hPa in three hours warns of strong wind.
Put the signs together. Pressure falling fast, high wispy cloud thickening from the west and a long swell arriving out of a calm sea all say the same thing: a depression with strong wind is on its way.
What should we do when a thunderstorm squall is coming?
Reef or drop the sails, put lifejackets on, shut the hatches and stow loose gear before the squall arrives: its first gust can be far stronger than the wind ahead of it and comes within minutes.
On a hot, sticky afternoon watch the tall cauliflower clouds that grow over the land. When a top spreads out flat like an anvil, it is a thundercloud. Under it comes a squall: sudden violent gusts, often from a new direction, heavy rain and lightning.
The first gust can be far stronger than the wind ahead of it, and it reaches you within minutes of the dark ruffled water appearing. Everything is easier to do before it arrives.
Questions from this topic, as the app asks them. Open one to see the answer.
The morning forecast says 'northerly, Force 5'. Which way is the wind blowing?
A. From the north, towards the south
Wind is always named by the direction it blows from.
Which Force on the Beaufort scale is this?
D. Force 6
Force 6 is 22–27 knots, a strong breeze.
What does the visibility part of this forecast warn you about?
B. In places you may see less than 1 km
In forecasts 'fog' means visibility under 1000 m; 'poor' means under 2 miles.
What wind do you expect by mid-afternoon?
A. A breeze blowing in from the sea onto the land
Land heats faster than sea; the air over it rises and a sea breeze blows in by the afternoon.
Close under the cliffs the water looks calm. What do you expect there?
A. Sudden strong gusts falling off the cliffs
Wind spilling over high land drops down the lee side in violent gusts.
You are keeping the barometer log. What do you tell the skipper?
C. It is falling fast — strong wind may be on the way
A fall of several hPa in three hours is a warning that strong wind is coming.
All 20 questions of this topic are in the app: practice by topic with the reason after every answer, your mistakes brought back, and a timed mock exam. Free, no sign-up, in the browser or in Telegram.