A full-powered vessel, 132 f t. long, crew of 16, it has a flashing incandescent electric light of 22,000 candle-power, compressed air fog whistle, radio-beacon and synchronized submarine oscillator. It is an oil-burning steam vessel, No. 112 (1936). Several light ships have Diesel engines, and 3 ships have Diesel-electric propul sion.
Lightships moored in the sea off the Atlantic coast, exposed to tropical hurricanes and other severe storms, receive special atten tion as to vessel design and moorings to ensure station perma nency. For years attempts to keep lightships off New York and Cape Hatteras failed.
Severe storms have sometimes torn lightships from their moor ings. Cast steel chain is being used for moorings, so as to better retain lightships on station. Mushroom anchors up to 4 tons are being used.
Buoys.—The American coast's great length and intricacies re quire 15,000 buoys. The increase in lighted buoys is a notable ad vance. In 1939, 1,881 lighted buoys were on station. Nearly all lighted buoys use acetylene gas compressed in tanks, set in buoy pockets, but electric lighted buoys are increasing in number. Steel buoys of various sizes are extensively used to mark channels and shoals. Wooden spars are being replaced advantageously by small inexpensive steel buoys. Though not very effective fog signals, there are 226 whistle buoys and 811 bell buoys, some of the latter provided with chimes having 4 different notes, to distinguish from the bells.
All buoys and moorings are relieved at least once a year, old buoys brought to depots, cleaned and repainted. Their great num ber makes this an important and time-consuming task. (See arti cle on Buoy.) Sound Fog Signals.—Radio-beacons, described later, are the most effective fog signal. Various types of sound signals, using compressed air or electricity, are employed, but their value is lim ited, due to short and undependable range, and the impracticability of taking accurate bearing on them. But, so far as may be fore seen, sound fog signals will remain indispensable. Steam whistles formerly used extensively, are being replaced by more efficient apparatus. Variously actuated electric sirens, reed horns and bells serve for minor sound signals.
The United States uses no explosive fog signals and but few signals (bells) operated by hand.
Though automatic sound fog signals would be of great value, there are, besides the bell and whistle buoys, only 29 bells actu ated by carbon dioxide gas; these are useful where a moderate signal suffices that can readily be reached, but are not dependable otherwise.
Nearly all fog signal machinery and apparatus is installed in duplicate for greater reliability.
The first successful radio-beacons were placed at three stations near New York in 1921 ; the system has now grown in the United States and outlying territories to 141 stations, about one-third the number in the world. The transmitting apparatus is generally timed to sound one out of each three minutes, during fog or low visibility; also at certain half or quarter hours in clear weather. Each station sends a characteristic code signal differing from any other within range. Signals are of interrupted continuous wave type, sent with tube transmitters; tests are being made with con tinuous wave signals; standard wave length is 1,000 metres (300 kilocycles per second), but to lessen interference between adja cent stations in congested localities, wave lengths have been stag gered somewhat, between 952 and 1,052 metres (315 and 285 kilocycles).
A few important stations, i.e., Nantucket lightship, are operated with 500 watts; the standard power for other coast stations, and on the Great Lakes, is 200 watts; for inland waterways as low as 71 watts are being tried. This system is extending rapidly. If conditions favour, bearings correct to I° or 2° up to 200 m. away are obtained. Rotating radio-beacons have not been introduced here, as they can not be placed on lightships, the most important radio-beacon stations.