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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In foggy conditions you hear one prolonged blast plus two short blasts every two minutes. What does this sound signal mean?

During foggy conditions, what does one prolonged blast every two minutes mean?

What is one possible meaning of a single prolonged blast of a horn?

A sailboat is underway in the fog. What sound signal should you hear?

A rapidly ringing bell every minute signals what?

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.

Fog Forecasting

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.

How to Prepare and Navigate in Fog

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.

Personal Safety During Fog

  • Have all the crew put on life jackets, as there will little time if a collision occurs.
  • Consider carefully before having the crew clip on [safety harnesses], as they must be able to jump clear in a collision.
  • If the weather is rough, the greater danger of falling overboard may require harnesses to be used.
  • The life-raft should be at the ready for instant release if needed.
  • Have red and white flares at hand.
  • In calm weather, consider putting the dinghy over the side, [ towing it astern ] and being available in the event of a collision.

Strategy for Sailing in Fog

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.

Strategy Out to Sea

  • Continue on course if out to sea, keeping a lookout and making fog sound signals.
  • If possible, proceed under sail, as engine noise limits the ability to hear other boats.
  • If in calm conditions and motoring is the only option, move at a practical speed to give good steerage way enabling the yacht to turn quickly if necessary.
  • Turn off the engine at regular intervals and listen for other vessels or navigation aids.
  • The mainsail should be hoisted, making the yacht visible to another vessel.

Strategy in Shipping Lanes

  • If in or near a busy shipping lane the first priority is to move out of it as soon as possible.
  • Sail into shallow water where there are no large vessels and if crossing a shipping channel, cross at right angles.
  • Establish the exact position of the boat and use the radio to make contact with surrounding vessels.
  • If there is suspicion that the yacht’s position is not being tracked by other vessel’s radar, send a Securite message giving the yacht’s position.

Strategy in Shallow Water

  • When in shallow water, either heave-to or anchor until the fog lifts and keep a lookout for other vessels that are also seeking shallow water.
  • When a harbour is nearby with a safe entrance and there is confidence in your navigation skills, make for it and do not rely solely on electronic aids to ensure your safe entry.
  • Using a depth sounder permits making way close the shoreline by choosing a [ seabed contour ] to follow. Correct for the height of the tide, and then change direction with some degree of confidence.
  • Approaching land or a chosen harbour, estimate your time of arrival, consult the tidal stream atlas, and initially aim for a point some miles upstream of your actual destination.

Maritime Fog Horn Sound Signals

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.

  • Under sail (and some other vessels): One prolonged foghorn horn blast and two short blasts every two minutes
  • Making way under power: One prolonged foghorn horn blast every two minutes.
  • Under way but not making way: Two long horn blasts at two-minute intervals.
  • Aground - under 100m (328ft): Three bells, rapid ringing, three bells, at one-minute intervals.
  • Aground - over 100m (328ft): Three bells, rapid ringing, three bells, a gong sounded aft, every minute.
  • At anchor - under 100m (328ft): Rapid ringing of bell forward in boat at one-minute intervals.
  • At anchor - over 100m (328ft): Rapid bell ringing forwards, gong sounded aft, at one-minute intervals.

Ship horn signals at sea and foghorn meaning and horn signals for boating.

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