Anemometers: Measuring Wind Speed for Marine Navigation

Introduction

An anemometer is a meteorological instrument used to measure wind speed. On a sailing yacht, motorboat or during a water sports activity, this measurement provides practical information about the conditions at a specific location and time. It helps sailors assess wind strength, compare local observations with weather forecasts and prepare decisions before departure or a manoeuvre.

A marine anemometer can be used on deck, at anchor, in a harbour, on a beach or ashore before setting out. Handheld models are particularly useful for measuring local wind without installing a permanent sensor. Some instruments display the measured speed directly, while others connect to a compatible smartphone to show readings, track changes and review measurement histories.

The Anemometer category at Nautic Way includes the Plastimo Windy handheld anemometer, dedicated accessories and the Vaavud Mjolnir, a compact model that uses a compatible smartphone to display measurements. These instruments address different wind-measurement needs, from occasional observations to tracking changes during outdoor and water-based activities.

What is an anemometer used for in navigation?

Wind speed directly affects sailing, comfort on board, anchoring conditions and preparation for manoeuvres. A local measurement complements information from marine weather forecasts, applications and instruments installed on board.

A handheld anemometer can be used to:

• Measure wind speed on deck or in an exposed area.

• Observe changes in wind before leaving harbour.

• Compare local conditions with weather forecasts.

• Monitor gusts and changes in wind strength, where the instrument supports these functions.

• Record readings in a logbook or for personal weather observations.

• Measure wind for dinghy sailing, kitesurfing, windsurfing and other outdoor activities.

An anemometer measures the wind at the point where it is used. This reading does not necessarily represent the wind offshore, at the masthead or in an area affected by terrain and buildings. Measurements should therefore be interpreted in relation to the environment, sensor height and observation conditions.

Understanding wind speed and measurement units

Anemometers can display wind speed in several units. In marine navigation, the knot is particularly common: one knot equals one nautical mile per hour, or approximately 1.852 kilometres per hour.

The most common units include:

• Knots (kn or kt): widely used in marine weather forecasts and navigation.

• Kilometres per hour (km/h): familiar for comparing wind with general weather forecasts.

• Metres per second (m/s): a common scientific unit for meteorological measurements.

• Beaufort scale: a classification of wind force based on observable effects, including its effect on the sea.

Conversions make it easier to compare measurements. For example, a wind speed of 10 knots is approximately 18.5 km/h or 5.1 m/s. The corresponding Beaufort force depends on the conventional ranges used; the scale provides a practical classification rather than a separate instrumental measurement.

If the anemometer supports several units, the navigator can select the one best suited to their usual practice and the data being compared.

Handheld anemometer or permanently installed wind sensor?

There are different ways to measure wind. The choice depends on how often measurements are needed, the type of boat and whether continuous data are required.

Handheld anemometers

A handheld anemometer is easy to carry and can be used in different locations. It is suitable for checking wind speed before departure, observing conditions at anchor or taking occasional readings. It does not necessarily require permanent installation on the boat.

The Plastimo Windy is an example of a handheld instrument. Its portable format allows local measurements to be taken according to the operating conditions and manufacturer’s instructions. Dedicated accessories, such as a mount or replacement wind-sensing assembly, may be useful depending on the instrument configuration.

Smartphone-connected anemometers

Some compact anemometers use a compatible smartphone to display measurements. The Vaavud Mjolnir is an example of this approach: the instrument connects to a compatible phone, which provides the interface for viewing the available data.

Depending on the device and application, users may be able to select different units, monitor wind-speed changes or consult measurement history. Smartphone compatibility, application functions and operating conditions should be checked before choosing this type of solution.

Wind sensors installed on a boat

Some sailing yachts use a permanent sensor mounted high on the mast to measure wind and transmit data to the onboard instruments. Depending on the system, the display may show apparent wind and, when the necessary additional data are available, calculate true wind.

This arrangement serves a different purpose from a handheld anemometer. A portable instrument is used for local readings, while an installed sensor supports continuous monitoring and integration with the boat’s navigation instruments.

Measured wind, apparent wind and true wind: what is the difference?

It is important to distinguish the wind measured locally by a handheld anemometer from the wind data used by the instruments on a moving sailing yacht.

Apparent wind is the wind experienced and measured from a moving boat. It depends on both the meteorological wind and the vessel’s movement. True wind refers to the wind relative to the Earth’s surface or the surrounding water, estimated from apparent wind and the vessel’s motion according to the available data and calculation method.

A handheld anemometer provides a measurement of airflow at its location. This reading can be affected by the boat’s superstructure, sails, nearby buildings or the user’s body. It therefore does not automatically provide the true wind used for sailing calculations.

For a more representative reading, choose an exposed location, avoid sheltered or turbulent areas and hold the instrument according to the manufacturer’s instructions.

How to use a handheld anemometer

Useful measurements begin with consistent use of the instrument. The user should check its measurement range, stated accuracy, operating conditions and reading procedure.

A simple procedure includes the following steps:

1. Check the instrument. Make sure the sensor is clean, moving parts turn freely where applicable and the instrument is ready for use.

2. Choose an exposed location. Avoid obstacles that may disturb airflow as far as possible.

3. Hold and orient the instrument correctly. Follow the manufacturer’s instructions, particularly for devices whose operation depends on orientation.

4. Wait for a stable reading. When the wind varies, observe several readings rather than relying on a single instantaneous value.

5. Record the conditions. If needed, note the time, location, exposure and any gusts.

6. Compare with the forecast. Use the local measurement as a supplement to marine weather information, not as a replacement.

This method helps improve interpretation and reduces errors caused by poor positioning or inconsistent use.

Practical example: assessing the wind before leaving harbour

A sailor is preparing for a sailing trip. The weather forecast indicates moderate wind, but the conditions in the harbour appear different. The sailor uses a handheld anemometer in a sufficiently exposed area, away from buildings and immediate obstructions.

Several readings are taken to distinguish the prevailing speed from occasional gusts. The results are then compared with the forecast, wind direction and observed conditions in the intended sailing area. If the readings vary considerably between locations, the sailor considers the possible effects of buildings, terrain or harbour structures.

This observation provides additional information for planning the departure, but it cannot by itself determine whether conditions are safe. The sailor must also consider sea state, forecast gusts, visibility, currents, the boat’s characteristics, crew experience and expected weather developments.

How to choose a marine anemometer

The right anemometer depends on its intended use and the technical characteristics of each model.

Important criteria include:

• Measurement range: check the minimum and maximum speeds the instrument can measure.

• Specified accuracy: review the manufacturer’s stated tolerance and the conditions under which it applies.

• Available units: select units suited to marine navigation and the weather data being compared.

• Readability: choose a display that is easy to consult in the intended operating conditions.

• Resistance to outdoor conditions: check information about water, salt spray, dust and impact resistance.

• Power and connectivity: determine whether the instrument works independently or requires a smartphone and application.

• Maintenance and spare parts: check the availability of accessories, mounts or replacement components.

The Plastimo Windy may suit users who need portable wind measurements on board. The Vaavud Mjolnir is an option for users who prefer a compact solution connected to a compatible smartphone. The choice between these approaches depends on usability preferences, compatibility and the functions required.

Maintenance and measurement limitations

An anemometer should be kept clean and used within the conditions specified by its manufacturer. Openings, moving parts and sensors should be protected from deposits that may interfere with operation. After use in salty or dusty environments, follow the model’s cleaning and drying instructions.

Measurement accuracy also depends on the surrounding environment. A reading taken behind a cabin, close to a sail or in a harbour surrounded by buildings may differ from one taken in an open area. A single value may not fully describe gusts or changes in wind speed over time.

For a more complete assessment, anemometer readings can be considered alongside weather forecasts, sea observations and, on an equipped sailing yacht, data from a masthead wind instrument.

Conclusion

An anemometer is a practical instrument for measuring wind speed and understanding local conditions before or during a water-based activity. A handheld model allows occasional measurements, while a smartphone-connected device can make readings and trends easier to view. Permanently installed sensors address the need for continuous monitoring and integration with onboard instruments.

When choosing a marine anemometer, consider its measurement range, accuracy, available units, resistance to outdoor conditions and ease of use. Used correctly and interpreted alongside weather forecasts, an anemometer provides useful information for the navigator without replacing sound judgement or a comprehensive assessment of conditions at sea.

FAQ – Marine anemometers

What is an anemometer used for on a boat?

It measures wind speed at the location where it is used. This helps the sailor observe local conditions and compare them with weather forecasts.

What is the difference between a handheld anemometer and an installed wind sensor?

A handheld anemometer is used for occasional measurements in different locations. An installed sensor generally provides continuous readings and may transmit data to the navigation instruments.

Which unit should I use to measure wind at sea?

Knots are widely used in marine navigation. Kilometres per hour and metres per second are also common. The important point is to compare data expressed in the same unit.

Does a handheld anemometer measure true wind?

Not necessarily. It measures wind at the sensor’s location. True wind used in sailing is derived from apparent wind and the boat’s movement using the appropriate data.

Does the Vaavud Mjolnir require a smartphone?

This model uses a compatible smartphone to display its measurements. Check compatibility and available functions before use.

How can I obtain a reliable wind measurement?

Choose an exposed location, hold the instrument according to its instructions, observe several readings when the wind varies and account for nearby obstacles.

Is an anemometer enough to decide whether to go to sea?

No. It provides a local wind-speed measurement, but a decision to sail must also consider forecasts, sea state, gusts, visibility, the boat and the crew.

How should a marine anemometer be maintained?

Follow the manufacturer’s instructions, keep the sensor clean, protect sensitive components and regularly check the instrument and its accessories.