This page details what foghorn blast sequences in foggy conditions indicate as well as marine fog horn sound signals at sea and foghorn meaning vessel sound signals for boats in fog aerosol air horn and maritime horn signals. Mist fog lights in fog systems and nautical navigation software for sailing boat yacht sailing weather marine fog horn as well as marine horn signals
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Resist putting to sea unless the fog is land-bound and conditions at sea are clear. If sailing when fog descends take steps to increase safety, the yacht’s visibility and use the correct fog sound signals and be aware of other boat fog horn signals.
Professional forecasters warn sailors of impending foggy conditions, but fog forecasting with a degree of success is possible if there is a humidity meter on the craft. When humidity reaches 90 to 95 percent, and sea water temperature is 5°C to 10°C, there is a high chance of fog.
An accurate way of fog forecasting is the use of a hygrometer to find the dew point temperature of the air. A [ hygrometer ] consists of two thermometers, one wet bulb, one dry bulb and the readings from these determines the relative humidity of the air.
With the air's relative humidity, its dew point temperature is found by referring to tables. If dew point temperature is a few degrees below the actual air temperature, expect fog as night approaches. If a hygrometer is not available, listen to the weather forecast transmissions, principally during settled conditions of high pressure and in spring and autumn.
When fog conditions appear when sailing, the safety of the crew and yacht should be the skipper’s first consideration. The first priority when navigating is to establish your position as exactly as possible at the onset of mist or fog. Knowing where you are, or cannot possibly be, is the essence of safe conduct with reduced visibility. Update your estimated position thereafter, at half-hourly intervals or when making major changes in direction.
Pay attention to tidal streams as they still function as whey would on a sunny day. Double-check all estimated positions and fixes, and verify them by using the echo sounder. If using GPS navigation, use known and tested waypoints.
Unless there is one permanently fitted, hoist a [ radar reflector ] high up the rigging as possible. All commercial vessels and many yachts use radar as a means of collision avoidance and it is for this reason a reflector is used. Switch on all navigation lights, delegate a crew member to use the fog horn and station extra lookouts equipped with a number of [ white flares ]. If motoring, place a lookout on the foredeck away from the noise of the engine.
The miniaturization and availability of electronic navigation equipment has changed the approach of long-time sailors to the dangers of fog and mist. Their ability to revert to using navigation skills when necessary is an advantage over those who rely completely on electronics.
Sight a buoy or other object which will provide an estimation of your visibility to others, or drop a bundle of paper over the side and find the time it takes before disappearing from sight. Having knowledge of the yacht's speed allows the distance to be worked out. If the yacht is fitted with radar, station an experienced crew member to monitor it. Do not rely on radar alone and still have lookouts on deck.
Strategy when sailing in foggy conditions depends on whether the yacht is close to land, in a busy shipping area, or well out to sea.
In fog, make use of the boat horn signals to indicate your presence to other boats. Navigational aids, such as buoys and lighthouses, are fitted with [ maritime sound signal apparatus ] so that they can be identified. The signal type emitted is marked on charts and in pilot books. Do not assume a direction for the maritime horn signal as it can be distorted by fog so stop and double-check the direction then proceed with caution.
A ship's presence, its size, and activity is indicated with a combination of maritime fog horn, bell, and gong signals. A boat under 12m (39ft) carries an sound signal in the form of compressed-air or [aerosol fog horn ]. Larger boats over 12m (39ft) carry a bell, and vessels over 100m (328ft) will also use a gong.
The use of appropriate foghorn sound signals in foggy conditions indicate whether the vessel is sailing or motoring, aground, or at anchor. Fog horn sound signals are either prolonged (four to six seconds) or short (one second). A bell can be sounded as a single ring or as a rapid ringing for five seconds, and a gong is rung rapidly. The meaning for common ship horn signals for boating are listed below. Keep a reference book on board detailing the full list of maritime fog signals as required by the International Regulations for Preventing Collisions at Sea and memorize the foghorn meaning.