Chapter - 16

Boat Handling In Fog

General Remarks About Sound

Sound is very erratic over the water, and depending upon sound alone has cost many a life at sea and many a vessel. Often there are belts and areas over which sound does not seem to carry and other phenomena also occur which change the direction that sound travels.

Mariners are cautioned that, while every endeavor will be made to start fog signals as soon as possible after signs of fog have been observed, they should not, when approaching the land in a fog, rely implicitly upon these fog signals, but should always use the lead, which in most cases will give sufficient warning. A fog often creeps imperceptibly toward the land and a vessel may have been in it some time before it is observed at a lighthouse. As sound is conveyed irregularly through the atmosphere, mariners are strongly cautioned that they must not place dependence on judging their distance from a fog signal by the power of the sound. Under certain conditions of the atmosphere the sound may be lost a short distance from the station, as there may be silent areas or zones, or the sound may carry much farther in one direction than in another, and these conditions may vary in the same locality within short intervals of time. Mariners must never assume that the fog signal is not in operation because they do not hear it, even when in close proximity. The above applies particularly to fog signals sounded in air, as steam or air whistles, sirens, horns, ordinary bells. Attention should be given to observing a fog signal in positions where the noises of the ship are least likely to interfere with the hearing, as experience shows that though such a signal may not be heard from the deck or bridge when the engines are running it may be heard when the ship is stopped or from a quiet position; it may sometimes be heard from aloft, though not on deck.

Speed Of Vessel In Fog

One of the principal rules of navigation in a fog is to use the greatest caution at all times, keeping the speed of the boat moderate, and having a careful regard to existing circumstances and conditions. When a fog signal of an approaching vessel is heard it is the duty of every captain to keep his vessel under absolute control, stopping if necessary until the danger of collision is over.

When Fog Signals Are To Be Sounded

The rules prescribed for use in fog are also to be followed both day and night in mist, falling snow or heavy rain storms.

What To Sound Fog Signal On

vessels falling in the class of motor vessels when under way should sound the fog signal on the whistle or siren, and sailing vessels and vessels towed should use the fog horn.

A prolonged fog blast means one of from four to six seconds duration.

Motor Vessel Underway

The inland rules provide that a motor vessel shall sound, when underway, one prolonged blast, at intervals of not more than one minute.

Fog Signal For Sailing Vessel

A sailing vessel in the starboard tack sounds one blast of the fog horn every minute and when on the port tack two blasts of the fog horn in succession every minute, and when the wind is abaft the beam, three blasts in succession.

Vessel At Anchor

Any vessel at anchor must ring the fog bell rapidly for a period of five seconds every minute.

Vessel Being Towed

Any vessel which is towing, being towed, engaged in work on a cable, or by accident or for any other reason can not get out of the way of an approaching vessel, gives a prolonged blast followed by two short blasts, at intervals not exceeding one minute.

Fishing Vessels

Fishing vessels, as drifters, trawlers, dredgers, and line fishing craft, if over 20 tons gross, must, when engaged in fishing, give aprolonged blast on the whistle or foghorn, according to whether they are driven by steam or sail, the blast to be immediately followed by ringing the bell.

Vessel Aground

Any vessel which has the misfortune to run aground, or, in the case of a fishing vessel, gets her gear fast to a rock or other obstruction, shall be considered at anchor, and make the signal necessary for such case.

Vessel Without Way On

A vessel underway, but with no way on, sounds two prolonged blasts in rapid succession every two minutes, according to the international rules. The inland rules make no special provision for a boat underway, but with no way on and the regular fog signal for a boat with way on is generally used in this case.

Fog Signals At Light Houses

The characteristics of the fog signals sounded by the various lighthouses, light ships, etc., are fully described in the Light List published by the U. S. Coast Guard.

Radiobeacons broadcast simple dot and dash combinations by means of transmitter emitting modulated continuous waves.

Diaphones produce sound by means of a slotted reciprocating piston actuated by compressed air. Blasts may consist of two tones of different pitch in which case the first part of the blast is high and the last of a low pitch. These alternate pitch signals are called "two-tone."

Diaphragm horns produce sound by means of a disc diaphragm vibrated by compressed air, steam, or electricity. Duplex or triplex horn units of differing pitch produce a chime signal.

Reed horns produce sound by means of a steel reed vibrated by compressed air.

Sirens produce sound by means of either a disc or a cup-shaped rotor actuated by compressed air, steam, or electricity.

Whistles produce sound by compressed air or steam emitted through a circumferential slot into a cylindrical bell chamber.

Bells are sounded by means of a hammer actuated by hand, by a descending weight, compressed gas, or electricity.

Are You Ready To Move Onto The Next Lesson? Click Here...