Sailing boats are powered by the wind, so understanding wind strength and direction is crucial to being a good sailor.

Why knots?

Sailors measure distances in nautical miles and speeds in nautical miles per hour or knots. A nautical mile is a bit longer than a land mile.

In the old days, sailors measured their speed by throwing a log attached to a rope into the water. The rope had knots tied into it at intervals of six feet. Sailors timed the number of knots they let out using a timer and used this information to work out the speed they were travelling at. This is the origin of the knot as a measurement of a ship's speed.

Wind speed

The strength of the wind is measured using the Beaufort Wind Scale, invented by Admiral Francis Beaufort in the 18th century. We still use this system today.

The strength of the wind is measured on a scale from 0–12, where 0 is complete calm and 12 is the strongest storm.

Photograph of Walker's patent harpoon ship log

D5333, Walker's patent harpoon ship log
© National Maritime Museum, London

Painting of Admiral Beaufort

BHC2541, Admiral Beaufort
© National Maritime Museum, London

Roll over these images of the states of the sea to find the ideal conditions for learning to sail.

Wind direction

The wind is measured by the direction it is travelling from.

Diagram illustrating wind direction

N to S is a northerly wind

W to E is a westerly wind

Highs and lows

The changes in the type of weather we experience are caused by high and low air pressure. Air moves from areas of high pressure to areas of low pressure. We call this movement of air wind. We are unable to feel changes in air pressure. But we can measure them with a barometer.

High air pressure
The weather is usually quiet and settled.

Low air pressure
We often get unsettled weather and sometimes strong winds and rain. Not good sailing weather!

Diagram showing high and low pressure

Onshore and offshore breezes

Near the coast we often get an onshore or offshore breeze. They are caused because the land heats up and cools down more quickly than the sea.

Wind blowing from the sea to the land = an onshore wind.
Tricky to launch your boat, but plain sailing coming home.

Wind blowing from the land to the sea = an offshore wind.
Easy to launch your boat, but be careful, you may be blown out to sea!

Diagram illustrating onshore and offshore winds

Find out more

For more fun facts about our weather go to the Met Office website

Screen shot from the quiz
Screen shot from the game