Boating in fog: sound signals, radar and Rule 19

Fog does not remove traffic, shoals or closing speeds; it removes the visual cues that normally make them easier to judge. A sound small-craft response therefore starts by buying time: slow early, organise the crew, make the vessel detectable and build a navigation picture from several independent inputs rather than one persuasive display.

Make the go-or-wait decision before visibility collapses

The safest fog passage may be the one postponed. Read the local forecast alongside the route, expected commercial traffic, depth constraints and places where the boat could wait clear of channels. Advection fog can travel and thicken over water, so a bright patch ahead is not evidence that the approach will remain open.

The US National Weather Service classifies marine visibility as very poor below 0.5 nautical miles, poor from 0.5 to under 2, moderate from 2 to 5 and good above 5. Those bands explain forecast language; they do not supply a universal safe speed. Stopping performance, sea state, background light, traffic density, sensor quality and the skipper's workload all change the usable margin.

Before landmarks disappear, mark the position and identify dangers, ferry routes, traffic lanes and an escape or holding area. Test the compass, chart or plotter, GPS, VHF, navigation lights, horn and radar if carried; ready the engine and steering, put on lifejackets and clear loose gear. Preparation should reduce the number of new tasks arriving when the crew most needs to listen.

Rule 19 changes the encounter model

Restricted visibility is wider than fog. The COLREG definition also includes mist, falling snow, heavy rainstorms, sandstorms and similar causes, and Rule 19 applies to vessels not in sight of one another while navigating in or near such an area. A skipper need not wait for a complete white-out before adopting restricted-visibility conduct.

Every vessel must use a safe speed suited to the circumstances; a power-driven vessel must also keep its engines ready for immediate manoeuvre. Safe speed is a continuing judgement, not a preset throttle position. A useful test is whether the boat retains enough observed and charted water to assess a contact, take substantial action and stop without entering the next hazard.

A proper lookout still uses sight and hearing, plus every appropriate available means. Put one crew member on lookout without competing cabin duties, open a screen or move to a listening position when safe, silence entertainment and note the apparent sector and time of every engine or fog signal. AIS is valuable for equipped transmitters, but an empty AIS screen never proves an empty sea.

Know what the fog signals actually describe

Rule 35 signals are made in or near restricted visibility by day or night. The common pleasure-craft cases below are a memory aid, not a substitute for the complete COLREG text or local rules.

“Underway” and “making way” are not interchangeable. Crew should know which condition the boat is in and be able to reach and operate the sound appliance; Rule 33 requires a whistle and bell at 12 metres or more, with a gong added from 100 metres. A vessel below the equipment threshold still needs a means of producing an efficient sound signal.

Do not convert loudness into distance. Wind, a closed wheelhouse, cliffs and atmospheric effects can bend or mask sound, and a bearing by ear may be deceptive. Record the first impression instead of polishing it into certainty; a signal apparently forward of the beam demands a conservative response unless collision risk has been ruled out.

Use radar as a sequence of observations

Radar contributes only when its controls and limitations are understood. Select a useful range and tune gain, sea clutter and rain clutter without suppressing small echoes; compare coastline and buoy returns with the chart to catch an orientation or setup error. Watch meaningful contacts over time, because one sweep cannot establish a dependable relative track.

For a vessel detected by radar alone, Rule 19 requires an assessment of close-quarters development and collision risk, followed by early avoiding action when needed. If that action is an alteration of course, avoid so far as possible turning to port for a contact forward of the beam unless overtaking, and avoid turning toward a contact abeam or abaft the beam.

That wording is not an automatic “turn right” command. Check bearing trend, range, own movement, navigable water and every other target, then verify that the action produces a clear improvement. VHF may exchange useful information, but uncertain vessel identification and informal passing agreements can make a confused picture worse; radio does not displace the collision rules.

A forward contact calls for less energy, not more guesswork

When another vessel's fog signal is heard apparently forward of the beam, or a close-quarters situation ahead cannot be avoided, Rule 19 requires speed to fall to the minimum at which the vessel can be kept on course. If necessary, take all way off and navigate with extreme caution until the danger has passed.

The practical response is deliberately plain: call all available hands, mark position and depth, check astern and abeam before reducing, ready propulsion and anchor, keep making the correct signals and refresh every plot. Stopping blindly in a fairway can exchange one risk for another, which is why a safe waiting area belongs in the passage plan.

Small craft should behave as though their radar return may be weak. UK Maritime and Coastguard Agency guidance warns that leisure vessels may not be detected by larger ships in time, and even a radar reflector can remain a difficult target. Correct lights, a well-positioned reflector and sound signals improve conspicuity, but they do not outsource collision avoidance.

Turn the rules into a short onboard routine

A card at the helm can divide the response into entry, monitoring and doubt. On entry: slow down, show navigation lights, begin the right signals, post the lookout, fix the position and ready the engine. While inside: update depth and contacts, cross-check radar, chart, compass and GPS, and repeatedly ask whether the current speed still leaves a real stopping option.

When doubt grows, avoid a chain of small late alterations. Remove speed, create thinking time, make any action substantial enough to be understood and measure its effect; if risk cannot be excluded, treat it as present. Normal sight-of-one-another rules become relevant only when the vessels can genuinely observe each other visually.

This final point is Batoo operational analysis rather than a new regulation: the best procedure is one another crew member can run without decoding the skipper's habits. Practise the horn, displays, roles and stopping response in clear weather. In restricted visibility, safety comes from a coherent system of lookout, speed, signals, plotting and an honest willingness to wait.