the principal harbors steamers and tugs usually keep a channel open. See "Ice" under the different headings. STORM WARNINGS Storm warnings are displayed by the United States Weather Bureau on the coasts of the United States and the Great Lakes. Small-craft warning.-A red pennant indicates that moderately strong winds that will interfere with the safe operation of small craft are expected. No night display of small-craft warnings is made. Northeast storm warning.-A red pennant above a square red flag with black center displayed by day, or two red lanterns, one above the other, displayed by night, indicate the approach of a storm of marked violence with winds beginning from the northeast. Southeast storm warning.-A red pennant below a square red flag with black center displayed by day, or one red lantern displayed by night, indicates the approach of a storm of marked violence with winds beginning from the southeast. Southwest storm warning.-A white pennant below a square red flag with black center displayed by day, or a white lantern below a red lantern displayed by night, indicates the approach of a storm of marked violence with winds beginning from the southwest. Northwest storm warning.-A white pennant above a square red flag with black center displayed by day, or a white lantern above a red lantern displayed by night, indicates the approach of a storm of marked violence with winds beginning from the northwest. Hurricane, or whole gale warning.-Two square flags, red with black centers, one above the other, displayed by day, or two red lanterns, with a white lantern between, displayed by night, indicate the approach of a tropical hurricane, or one of the extremely severe and dangerous storms which occasionally move across the Great Lakes and Atlantic coast. These warnings are displayed at all stations on the Atlantic and Gulf coasts of the United States and on the following islands in the Atlantic: Jamaica, Turks Island, Bermuda, Haiti, Curaçao, Porto Rico, Virgin Islands of the United States, St. Kitts, Dominica, Barbados, Trinidad, St. Lucia, St. Vincent, Grenada, Swan Island, and Cuba. The following are the storm warning display stations within the limits covered by this volume: RADIO SERVICE The supervision of radio communication in the United States, including the Hawaiian Islands, is controlled by the Department of Commerce and the Federal Radio Commission. A list of the radio stations of the United States, including shore stations, merchant vessels, and Government vessels; Radio Communication Laws and Regulations of the United States; and Amateur Radio Stations of the United States are published by the department. Either of the first two publications can be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C., price, 15 cents each; the last one, 25 cents. Changes or additions to the stations and to the laws and regulations are published in bulletins issued monthly; price, 5 cents per copy or 25 cents per year. The International List of Radio Stations of the World (edition in English) can be procured from the International Bureau of the Telegraphic Union (Radiotelegraphic Service), Berne, Switzerland. In addition to the information contained in the list of the United States stations published by the Bureau of Navigation, the international list shows geographical locations, normal ranges in nautical miles, radio systems, and rates. Supplements to the international list will be issued monthly and will contain new stations and tables of alterations. Inquiries as to the subscription prices of these lists should be made direct to the Berne bureau at the address given above. Remittances to Berne should be made by international postal money orders. Time signals.-Radio time signals are sent daily from United States naval radio stations as follows: From the station at Arlington (call letters NAA) signals are sent out at noon and 10 p. m., standard seventy-fifth meridian time, on wave lengths of 2,677 and 4,409 meters, A. C. W. They are repeated automatically from the station at Annapolis (NSS) on a wave length of 17,130 meters, continuous wave, and from the station at Key West (NAR) on a wave length of 2,939 meters, tube. Lag constants have been determined for these stations, as follows: Arlington, 0.09 second; Annapolis, 0.09 second; and Key West, 0.28 second. Should the Arlington station not be working, time signals will be sent at noon daily, Sundays and holidays excepted, from the stations at New York, Norfolk, and Charleston. The signals begin at 5 minutes before the hour and continue for 5 minutes. During this interval every tick of the clock is transmitted except the twenty-ninth second of each minute, the last 5 seconds of each of the first 4 minutes, and finally the last 10 seconds of the last minute. The time signal is the beginning of the dash after this long break. Hydrographic information, weather reports, and other information of benefit to shipping are sent out from these stations. Radiocompass bearings. The increasing use of radio directional bearings for locations of ships' positions at sea, especially during foggy weather, has made it particularly desirable to be able to apply these radio bearings taken on shipboard or sent out by the shore stations directly to the nautical chart. These radio bearings 34370°-27-2 are the bearings of the great circles passing through the radio stations and the ship, and unless in the plane of the Equator or of a meridian, would be represented on a Mercator chart as curved lines. Obviously it is impracticable for a navigator to plot such lines on his chart, so it is necessary to apply a correction to a radiocompass bearing to convert it into a Mercator bearing; that is, the bearing of a straight line on a Mercator chart laid off from the sending station and passing through the receiving station. On page 14 is given a table of corrections for the conversion of a radio bearing into a Mercator bearing. It is sufficiently accurate for practical purposes for distances up to 1,000 miles. The only data required are the latitudes and longitudes of the radiocompass stations or radio beacons and of the ship by dead reckoning. The latter is scaled from the chart and the former either scaled from the chart or taken from the list of radiocompass stations and radio beacons listed in the Coast Pilots, in the light and buoy lists published by the Lighthouse Service, or in the publication, Radio Aids to Navigation (H. O. No. 205), issued by the Hydrographic Office, United States Navy. The largest scale chart available should be used for this purpose. The table is entered with the difference in longitude in minutes between the ship and station (the nearest tabulated value being used), and opposite the middle latitude between the ship and station (to the nearest tabulated value) the correction to be applied is read. The sign of the correction, when bearings are read clockwise from north, will be as follows: In north latitude, the plus sign is used when the ship is east of the compass station; the minus sign is used when the ship is west of the compass station; in south latitude, the minus sign is used when the ship is east of the compass station; the plus sign is used when the ship is west of the compass station. If the radio bearings are observed on the ship, the signs will be reversed. The corrected bearing is then the Mercator bearing from ship to the sending station, and to facilitate plotting 180° should be added to it and the result plotted from the sending station. Should the position by dead reckoning differ greatly from the true position of ship as determined by plotting the corrected radio bearings, a retrial should be made, using the new value as the position of the ship. Example.-A ship in latitude 37° 20′ N., longitude 69° 20′ W., by dead reckoning receives a radio bearing of 64° from a radiocompass station located in latitude 35° 14′ N., longitude 75° 32′ W. Find the Mercator bearing of the ship from the station— Radiocompass station latitude_ Dead reckoning position of ship----. Middle latitude__ 35° 14' N., long. 75° 32′ W. 37 20 36 17 69 20 Diff. 372 Entering table with difference of longitude = 360', which is the nearest tabulated value to 372', and opposite 36° middle latitude (the nearest tabulated value to 36° 17') the correction 106' is read. The ship being east of the station the correction is plus. The Mercator bearing will then be the radio bearing received plus the correction from the table, 64° 00′+106′ = 64° +1° 46′ = 65° 46′. For more accurate determinations the following formula should be used and on which the table of corrections is based: Formula for the conversion of radio bearings into Mercator bearings.-The Mercator bearing is equal to the radio bearing received, plus or minus one-half the convergence of the meridians in minutes, which expressed as a formula is M = Mercator bearing required. R=radio bearing received from the radiocompass station. D= difference in longitude, in minutes, between the radiocompass station and the ship's position by dead reckoning. B-latitude of the radiocompass station. B'=latitude of the ship's position by dead reckoning. Example.-A ship in latitude 37° 20' N., longitude 69° 20′ W., by dead reckoning receives a radio bearing of 64° from a radiocompass station located in latitude 35° 14' N., longitude 75° 32′ W. Find the Mercator bearing of the ship from the station. By the formula R=64° D=75° 32′ - 69° 20′ = 6° 12′ =372' B=37° 20' Substituting these values in the formula, and observing that since the ship is in north latitude and east of the radiocompass station sign is used (see p. 12 for determination of signs), we have— the M=64°+186' × 0.59176 = 64°+110′ = 64°+1° 50′ = 65° 50′ Table of corrections, in minutes Mid. L. BY 30 60 90 120 150 180 210 240′ 270 300 330 360 390 420 450 480 510′ 540' 570′ 600' 20 120 126 197 174 176 178 154 167 180 113 Radiobeacons (fog signals). The following radiobeacons, operated by the United States Lighthouse Service, will be of use to vessels navigating within the approximate limits of this volume: Portland Lightship: Groups of 1 dash and 2 dots___. 60 seconds. 120 seconds. Clear weather transmission: 5.30 to 6 and 11.30 to 12, both a. m. and p. m. Boston Lightship: Groups of 1 dash and 1 dot__. 60 seconds. 120 seconds. Clear weather transmission: 2.30 to 3 and 8.30 to 9, both a. m. and p. m. Nantucket Shoals Lightship (call letters WWAH): Groups of 4 dashes. Silent---- Fire Island Lightship (call letters WWAN): Clear weather transmission: Second 15 minutes of each hour, day and night. 60 seconds. 120 seconds. Groups of 2 dashes. 60 seconds. Silent-- 120 seconds. Clear weather transmission: 5.30 to 6 and 11.30 to 12, both a. m. and p. m. |