Diving Flags: Signaling the Presence of Divers at Sea

Introduction to diving flags

A diving flag is a maritime signaling device used to warn other water users that divers are underwater. Displayed from a dive support vessel, a suitable diving float or another appropriate support, it makes diving activity more visible and helps reduce the risk of collisions between divers and boats.

Scuba diving sometimes takes place in areas used by recreational vessels, fishing boats and powered watercraft. When a diver is underwater, their position may not be visible from the surface. A diving flag therefore identifies an area where other water users need to exercise particular caution.

The Diving Flags category at Librairie Maritime Nautic Way includes the red flag with a white diagonal stripe, as well as a set combining the diving flag with the International Code Flag Alpha. These models serve different signaling purposes and should not automatically be treated as interchangeable. Their use must take account of the local maritime context, applicable navigation rules and the type of support from which they are displayed.

The two main flags associated with diving

The blue-and-white Alpha flag

The Alpha flag belongs to the International Code of Signals. It is recognizable by its blue-and-white design and distinctive swallowtail shape. It indicates that a vessel is signaling the presence of a diver and asks other vessels to keep clear and proceed slowly.

This signal is particularly important when a vessel is supporting divers underwater. It alerts other navigators that diving operations are taking place and that people may be submerged nearby.

The Alpha flag does not replace safe navigation practices. The support vessel must choose an appropriate position, monitor its surroundings and comply with the applicable rules. Other water users must interpret the signal in context and maintain a safe distance.

The red flag with a white diagonal stripe

The red flag crossed by a white diagonal stripe is widely recognized in recreational scuba diving. It indicates the presence of divers in the water and may be displayed from a buoy, vessel or other suitable support, depending on local conditions and requirements.

This design is often called the international diving flag or the “Diver Down” flag. It is distinct from the Alpha flag, even though both are associated with diving safety.

Recognition and legal requirements for the red-and-white diving flag vary between countries and navigation areas. Local regulations should therefore be checked rather than assuming that this flag replaces the Alpha flag everywhere.

Why distinguish between the two flags?

The Alpha flag is part of the International Code of Signals. The red flag with a white diagonal stripe is widely used for recreational diving, but its regulatory status differs between jurisdictions.

A dive support vessel should carry and display the flag required by the applicable rules. Where useful and permitted, an additional flag may help divers and recreational boaters recognize the activity. The choice should reflect local requirements, the vessel’s characteristics and the conditions in which the dive takes place.

When should a diving flag be used?

A diving flag is useful whenever people are underwater or operating within a designated diving area.

• Diving from a vessel: the flag identifies the support vessel’s activity and warns nearby boats.

• Diving from a buoy: a solo diver may use a suitable floating signaling device where local rules and conditions permit.

• Club diving sessions: the flag helps make the activity area identifiable to other water users.

• Open-water diving: it helps indicate a diver’s presence when the person cannot easily be seen from the surface.

• Diving in busy areas: it provides an additional visual warning, without removing the need for proper supervision and planning.

A diving flag alone cannot guarantee safety. Weather, currents, underwater visibility, marine traffic and the distance from other vessels remain important risk factors.

Choosing a suitable diving flag

The right flag depends on how it will be used, the support on which it will be mounted and the conditions in which it needs to remain visible.

Dimensions and visibility

The flag must be large enough to allow other water users to identify the signal at an appropriate distance. A flag displayed on a small buoy is used in different conditions from one hoisted on a boat. The height at which it is displayed, sea state, light conditions and visual obstructions also affect visibility.

A flag should not be hidden behind a sail, deck structure or other equipment. On a floating device, the pole should be high enough to keep the flag above the waves as far as practicable.

Fabric and marine durability

A diving flag is exposed to wind, salt water, ultraviolet radiation and repeated handling. Its fabric should be suitable for marine use and retain sufficient colour contrast to keep the signal recognizable.

Models in this category include flags made from marine-grade gauze fabric. Depending on the model, features may include UV treatment, reinforced edges or suitable attachment fittings. Check the specifications of each flag rather than assuming that all models have identical features.

Mounting on a vessel or buoy

The flag should be securely mounted and clearly visible. Depending on the support, installation may require a halyard, rings, reinforcing straps, a pole or a suitable floating device.

Before divers enter the water, check that the flag is attached correctly, can be raised or deployed promptly and is unlikely to detach in wind or as the vessel moves.

Navigation safety around divers

A diving flag tells other water users that extra caution is required. Divers may be near the support vessel, drift with the current or surface at a location slightly different from the planned entry point.

In France, official recreational boating safety guidance advises vessels to pass at least 100 metres from flags indicating the presence of divers. Exact obligations and applicable rules should always be checked for the navigation area and circumstances.

Good practice includes:

• reducing speed and avoiding sudden manoeuvres near the marked area;

• maintaining a safe distance from the flag, support vessel and divers;

• carefully monitoring the water’s surface, especially when visibility is limited;

• taking account of currents and possible diver drift;

• avoiding unnecessary passage through an active diving area;

• complying with local rules for signaling, bathing areas and underwater activities.

A flag is a visual warning, not a physical barrier. A proper lookout and cautious navigation remain essential, even when the signal is clearly visible.

Maintaining and storing a diving flag

The marine environment can accelerate wear to both fabric and fittings. Salt, moisture, sunlight and strain on attachment points may gradually damage a flag.

A few simple measures can help preserve its visibility and service life:

• rinse the flag with fresh water after significant exposure to sea spray;

• allow it to dry completely before storage;

• avoid leaving a damp flag in a closed bag for extended periods;

• inspect seams, reinforcement and attachment points;

• check that the colours remain sufficiently distinct;

• replace a flag that is torn, faded or difficult to identify.

The flag should remain easy to access alongside the diving and safety equipment. Clearly organized storage makes it easier to retrieve the correct flag before a trip and check its condition during vessel preparation.

Diving flags and nautical preparation

Preparing for a dive involves more than checking underwater equipment. It also includes planning for the support vessel, communication equipment, weather, knowledge of the area and applicable navigation rules.

Nautical charts and reference publications, including those associated with Shom, Admiralty and NGA, may support general passage planning when their coverage and intended use are appropriate for the area. For diving-specific requirements, the relevant safety rules and local regulations must also be consulted.

Before departure, a practical check should include the required flag, its condition, the mounting arrangement, communication equipment and the procedure to follow if conditions change. For a group dive, it is also useful to ensure that all participants understand the signals in use and the safety procedures.

Conclusion

A diving flag plays an important role in signaling underwater activity. The blue-and-white Alpha flag and the red flag with a white diagonal stripe are distinct signals, and their use depends on the context and applicable regulations. Choosing the correct design, dimensions and mounting arrangement helps ensure that the signal remains visible under actual navigation conditions.

Proper signaling must always be combined with a careful lookout, an appropriate safety distance and compliance with local rules. Regular maintenance of the fabric and fittings helps keep the flag clearly visible and ready for future diving trips.

FAQ — Diving flags

What is a diving flag used for?

It warns other water users that divers are underwater or that diving activity is taking place nearby. It makes the area more visible but does not replace navigation and safety procedures.

What is the difference between the Alpha flag and the red-and-white diving flag?

The blue-and-white Alpha flag is part of the International Code of Signals and indicates the presence of a diver, asking other vessels to keep clear and proceed slowly. The red flag with a white diagonal stripe is widely used for recreational diving. Their status and use should be checked against local regulations.

Which flag should a dive support vessel display?

The vessel should display the signal required by the regulations applicable to its location and type. An additional flag may be useful when permitted and when it improves recognition of the diving activity.

Can a solo diver use a flag on a buoy?

Yes. A suitable floating device carrying a diving flag can indicate the presence of a solo diver, subject to local rules and safety conditions.

How far away should boats pass from a diving flag in France?

Official French recreational boating safety guidance advises vessels to pass at least 100 metres from flags indicating the presence of divers. Check the rules for the specific area and maintain an appropriate safety margin.

How do I choose the right size of diving flag?

Consider the mounting support, viewing distance, display height and sea conditions. The signal should remain visible and should not be obscured by vessel equipment or waves.

How should a diving flag be maintained?

Rinse away salt with fresh water, allow the fabric to dry completely before storage and regularly inspect the seams, fittings and colour contrast.