95 98 23 30 62 145 153 67 30 34 109 56 902 36 54 97 691, 096 24 97 54 881 49 102 571, 081 63 956 10 60 25 637 17 75 47 552 3 45 71 44 633 Cornfield Point Lightship.--103 98 35 17 30 106 158 Ice. In severe winters some of the harbors are closed to navigation by ice, but the principal harbors are usually kept open by the steamers and towboats. There is usually some drift ice on Monomoy and Nantucket Shoals and in Nantucket and Vineyard Sounds, Buzzards and Narragansett Bays, and Long Island Sound. For ice in Long Island Sound see page 117. Additional information concerning ice conditions is given under the descriptions of the tributaries. WEATHER 9 STORM WARNINGS Storm warnings are displayed by the United States Weather Bureau at numerous places 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. 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 Federal Radio Commission. Time signals.-Radio time signals are sent daily from the United States naval radio stations at Arlington, Va. (call letters NAA) and Annapolis, Md. (NSS). For the latest information as to time, frequency in kilocycles, and type of emission see H. O. No. 205, Radio aids to Navigation, issued by the Hydrographic Office, United States Navy. The signal consists of the transmission of a dot (.) for every second, omitting the twenty-ninth, fifty-first, fifty-sixth, fifty-seventh, fifty-eighth, and fifty-ninth second during the first minute; in the second minute the twenty-ninth, fifty-second, fifty-sixth, fiftyseventh, fifty-eighth, and fifty-ninth second will be omitted; in the third minute the twenty-ninth, fifty-third, fifty-sixth, fifty-seventh, fifty-eighth, and fifty-ninth second will be omitted; in the fourth minute the twenty-ninth, fifty-fourth, fifty-sixth, fifty-seventh, fiftyeighth, and fifty-ninth second will be omitted; in the fifth minute the twenty-ninth, fifty-first, fifty-second, fifty-third, fifty-fourth, fifty-fifth, fifty-sixth, fiftyseventh, fifty-eighth, and fifty-ninth second will be omitted; at the sixtieth second a one-second dash (-) will be sent, the beginning of which is the time signal. This is followed by the letters VA. In the event of an error occuring in the signal, another time signal will be transmitted one hour later. Hydrographic information, weather reports, and other information of benefit to shipping are sent out from these stations. RADIOBEACONS The United States Lighthouse Service operates radiobeacons in or near the area covered by this volume at the following places: For details as to frequencies, geographic positions, signals, and thick and clear weather transmission, see Light Lists of the Lighthouse Service or Hydrographic Office publication No. 205. These radiobeacons are intended for the use of vessels equipped with radio compasses. While the use of radiobeacons should not lead a mariner to neglect other precautions, such as the use of the lead, etc., during thick weather, the bearings will greatly reduce the dangers incident to navigation in the fog. The bearings of the radiobeacon may be determined with an accuracy of approximately 2° and at distances considerably in excess of the range of visibility of the most powerful coast lights. The RADIO DIRECTION FINDER SERVICE 11 apparatus is simple and may be operated by the navigator without the assistance of a radio operator or without knowledge of the telegraph code. The radio direction-finding apparatus consists of a radio receiving set, similar in operation to those used for radio telegraph or telephone reception, and a rotatable coil of wire in place of the usual antenna. By rotating the coil, the intensity of the signal received from the transmitting station is made to vary, and by noting the position of the coil when the signal is heard at its minimum intensity, the bearing of the transmitting station is readily obtained. It is important to note that a bearing of an incoming radio wave is subject to errors not unlike the deviation of the magnetic compass. Those using radio direction finding aboard ship are cautioned to bear these errors in mind and to keep the radio compass calibrated at all times. This may be done during clear weather by comparing the bearing obtained with the radio compass with the bearing as obtained by visual methods in general use. All radio bearings are subject to what is called "night effect," a variable error sometimes experienced near nightfall and sunrise. The uncertainty due to this cause may be lessened by taking repeated radio bearings. The signals from the radiobeacons have definite characteristics for identifying the station, and bearings may be obtained with even greater facility than sight bearings on visible objects. At some of the stations the radio and sound signals are synchronized for distance-finding purposes. See page 10. A general description of this method of navigation and the instruments required is given in Lighthouse Service publication, Radiobeacons and Radiobeacon Navigation, which may be obtained from the Superintendent of Documents, Washington, D. C., price 15 cents. RADIO DIRECTION-FINDER STATIONS United States naval direction-finder stations will furnish radio bearings to mariners of all vessels equipped with radiotelegraphic transmitters. While the use of these bearings should not lead a mariner to neglect other precautions, such as use of the lead, etc., during thick weather, these bearings will greatly reduce the dangers incident to navigation in the fog. Accuracy of bearings.-The accuracy with which bearings can be taken depends on various conditions and, while bearings taken by a station can generally be considered accurate to within 2°, the Government can not accept any responsibility for the consequences of a bearing being inaccurate. In the case of bearings which cut the coast line at an oblique angle, errors of from 4° to 5° have been reported. Bearings obtained between about one-half hour before sunset and one-half hour after sunrise are occasionally unreliable. It is probable that the accuracy of a bearing is also affected if the ship's transmitting instrument is not adjusted to the correct wave length. Bearings signaled as approximate" or "second class" should be regarded with suspicion as being subject to considerable error. The maximum distance for which bearings from these stations are accurate is 150 miles. 66 161875°-33-2 Direction-finder stations used as radiobeacons.-A naval direction-finder station when used as a radiobeacon, transmits upon request its call sign for 45 seconds on 375 kc (800 m). The following list of naval radio direction-finder stations will be of use to vessels navigating the approximate limits of this volume: The above stations are noted on the charts by the symbol "N. R. C." For a complete description of naval direction-finder stations together with directions for their use, see Hydrographic Office publication No. 205, Radio Aids to Navigation. CONVERSION OF RADIO BEARINGS TO MERCATOR 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 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 radio 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 13 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 radiobeacons or direction-finder stations 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 radiobeacon and radio direction-finder stations found in the light list or Hydrographic Office publication No. 205. The table is entered with the difference of longitude in degrees between the ship and station (the nearest tabulated value being used), and opposite the middle latitude between the ship and station, the correction to be applied is read. When bearings are taken from the ship, the sign of the correction (bearings read clockwise from the north) will be as follows: In north latitude, the minus sign is used when the ship is east of the radiobeacon and the plus sign is used when the ship is west of the radiobeacon. In south latitude, the plus sign is used when the ship is east of the radiobeacon, and the minus sign is used when the ship is west of the radiobeacon. To facilitate plotting, 180° should be added to the corrected bearing, and the result plotted from the radiobeacon. |