United States naval radiocompass stations will furnish radio bearings to mariners of all vessels equipped with radiotelegraph transmitters. While the use of these bearings should not lead a mariner to neglect other precautions, such as the use of the lead, etc., during a fog, these bearings will greatly reduce the dangers to navigation for mariners who are compelled for any reason to proceed during foggy or misty weather.

These radiocompass stations are provided, primarily, to assist the mariner in closing the land during fog or poor visibility, but they may also be used to obtain the positions of vessels at sea in radiocompass range, about 150 miles, when for any reason positions can not be obtained by other means. The maximum distance for which bearings from these stations are accurate is 150 miles. (See preceding pages for reduction of observed bearings to Mercator bearings.) Radiocompass stations are divided into two classes: (a) Single stations, operating independently and furnishing a single bearing. (b) Harbor entrance groups. All stations in harbor entrance groups are connected to and controlled by the master station. All stations of the group take bearings simultaneously and these bearings are transmitted to the ship requesting them by the control

station.

Where only one radiocompass station is available, the mariner may fix his position by two or more bearings from the station with the distance run between, or may use the bearings as a line of position, or as a danger bearing. Or the bearing may be crossed with a line of position obtained from an observation of an astronomical body to establish a fix.

Wave lengths. All independent and group radiocompass stations keep watch on 375 kilocycles (800 meters). Only this wave should be used to call and work with these stations.

Hours of service.-During the first 10 minutes of each hour during clear weather radiocompass stations ordinarily will not be guarding this wave. Ships are requested to confine their requests for bearings during clear weather to the remaining 50 minutes of the hour, as far as is practicable. Should a station chance to hear a request for a bearing during the first 10 minutes of the hour, the required bearing will be given. During the remaining 50 minutes and at all times during inclement weather, all radiocompass stations will be continuously guarding the 375-kilocycle (800-meter) wave.

Calling a radiocompass station. To obtain a bearing from independent radiocompass stations, call the station from which the bearing is desired in the usual manner and request bearings by means of the conventional signal given hereafter. Simultaneous bearings from two or more compass stations can be obtained by making the call include the other compass stations desired. To obtain bearings from the harbor entrance compass stations, carry out the procedure previously given. The compass control station only will answer. Conventional signals.-The following abbreviated signals will be

used:

66

Procedure in detail.-(a) A ship calling the radiocompass station or compass control station should make the abbreviation QTE?" ("What is my true bearing?"). This request will be answered by the radiocompass station or control station, and when ready to observe the radio bearing it will send the signal" K," indicating to the ship to commence "testing"; that is, repeating its distinguishing signal for a period of 50 seconds. The signal should be made slowly, with the dashes considerably prolonged.

(b) The testing should be made on 800 meters, upon the completion of which the ship should await reply from the radiocompass station.

(c) The radiocompass station or control station will then reply, repeating the abbreviation "QTE" ("Your true bearing from

was

degrees"), followed by the bearing in degrees given by a group of three figures 000 to 359, indicating the true bearing in degrees of the ship station from the radiocompass station, and then the time group, giving the time of observations in local standard time. In the case of more than one radiocompass connected by land line only, the station originally called will answer. This station will combine all the bearings taken by itself and associated stations into one message, which gives each bearing observed immediately after the name of the station making the observation. All compass stations transmit on 800 meters.

Danger from reciprocal bearings.-Attention is invited to the fact that when a single bearing is furnished there is a possibility of an error of approximately 180°, as the operator at the compass station can not always determine on which side of the station the vessel lies. Certain radiocompass stations, particularly those on islands or extended capes, are equipped to furnish two corrected true bearings for any observation. Such bearings when furnished vessels may differ by approximately 180°, and whichever bearing is suitable should be used.

Caution.-Mariners receiving bearings which are evidently the approximate reciprocal of the correct bearing should never attempt to correct these bearings by applying a correction of 180°, as such correction would not include the correction necessary on account of deviation at the compass station. An error of as large as 30° may be introduced by mariners applying an arbitrary correction of 180° to such bearings. Vessels receiving bearings manifestly requiring an approximate 180° correction should request the other bearing from the radiocompass station if not previously furnished.

Bearings, except in the case of approximate reciprocal bearings, should be accurate within 2° of arc, provided the transmitting equipment on board vessels is tuned sharply to 800 meters. Operators should use sufficiently wide coupling to obtain low decrement. If radio transmitters are not tuned sharply, it is difficult to obtain bearings that are sufficiently accurate for navigational purposes.

When bearings from three or more compass stations are not over 2° of arc in error, but do not meet at a fixed point, the geometric center of the triangle formed by the bearings can generally be taken as the approximate position of the vessel. Mariners, until thoroughly familiar with the system, are advised to use radiocompass stations frequently, especially in clear weather, when positions of

vessels can be accurately fixed in order to accustom operators to the procedure and to acquaint themselves with the degree of accuracy and dependability of bearings furnished by the radiocompass stations.

Reports. In order that the operation of shore radiocompass stations may be checked, mariners obtaining bearings are requested to forward a brief report to the Director Naval Communications, Navy Department, Washington, D. C., containing the following particulars:

1. Name of ship.

2. Name of radiocompass station.

3. Date and local standard time at which radio bearing was taken. 4. Bearings given by radio station.

5. Estimated position of ship at above time and dates by methods other than radio.

6. The probable degree of accuracy of the estimated position. 7. Weather conditions at above time.

8. Remarks, if any.

9. Signature of master or responsible navigating officer.

There is no charge for bearings furnished by the United States naval radiocompass stations.

Radio fog signals.-The following radio fog signals are operated on the Pacific coast by the United States Lighthouse Service. Stations for which no call letters are given do not maintain radio communication service:

The ships and stations transmit continuously during thick or foggy weather and from 9 to 9.30 a. m. and 3 to 3.30 p. m. during clear weather. Blunts Reef, Columbia River, and Swiftsure Bank Lightships also transmit during the first 15 minutes of each even hour from 10 p. m. to 6.15 a. m., in clear weather (all 120th meridian time).

At about 8 a. m., 12 noon, and 8 p. m. daily each lightship will broadcast, on 600-meter wave lengths, weather reports pertaining to

existing weather conditions in the immediate vicinity of the lightship and will furnish such weather reports at other times to vessels requesting them. These reports cover only actual weather conditions and forecasts can not be furnished.

These radio fog signals are intended for the use of vessels equipped with radiocompass. By means of this radiocompass (also termed radio direction finder) the bearing of the radio fog-signal station 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 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 radiotelegraph 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 caused 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 the bearing of an incoming radio wave is subject to errors not unlike the deviation of a magnetic compass. Those using radio direction finding on shipboard are cautioned to bear these errors in mind and to keep radiocompasses calibrated at all times. This may be done during clear weather by comparing the bearing obtained with the radiocompass with the bearing as given by other methods in general use. All radiocompasses are subject to what is called "night effect," an indeterminate error sometimes experienced near nightfall and sunrise.

The signals from the lightships and stations have definite characteristics for identifying the stations, as have the flashing lights and sound fog signals, and bearing may be obtained with even greater facility than sight bearings on visible objects. The radio fog signals are transmitted on a wave length of 1,000 meters, which is exclusively reserved for this purpose to avoid interference.

A general description of this method of navigation and the instruments required may be obtained from the Commissioner of Lighthouses, Washington, D. C., upon request. The Bureau of Standards Scientific Paper No. 428, the Radio Direction Finder and Its Application to Navigation, may be obtained from the Superintendent of Documents, Washington, D. C., for 15 cents.

Radiotelegraphic broadcasts of weather information.-The United States Weather Bureau issues daily (Sundays and holidays included) bulletins containing weather reports, forecasts, and warnings for the benefit of marine and aviation interests in the eastern waters of the Pacific and in the States bordering on that ocean. These bulletins are broadcast from naval radio stations.

A major bulletin is broadcast from the San Francisco Naval Radio Station (call letters NPG) twice daily as follows:

Morning bulletin at 9 a. m. (one hundred and twentieth meridian time) on a wave length of 7,005 meters (42.8 kilocycles).

Evening bulletin at 7.30 p. m. (one hundred and twentieth meridian time) on a wave length of 7,005 meters (42.8 kilocycles) and 2,776 meters (115 kilocycles) simultaneously.

The bulletins are divided into two parts and invariably begin with the letters USWB (United States Weather Bureau). The first part consists of upper air data and surface weather conditions. Weather reports from ships in the North Pacific Ocean follow the reports from land stations. The second part consists of a summary of general atmospheric pressure distribution over land and sea, including the locations of "high" and "low" areas, and the barometer readings at their centers; wind and weather forecasts for Pacific offshore areas; storm warnings for these areas; and flyingweather forecasts for each of three aviation zones.

Complete details of the service furnished by this and other stations, including the method of decoding the bulletins, is included in Weather Bureau Circular No. 10-Radio (second edition revised), which will be furnished free upon application to any United States Weather Bureau office on the Pacific coast.

Free medical advice to seamen by radio.-The Seamen's Church Institute of New York announces that, through the cooperation of the Seamen's Church Institute with the United States Public Health Service, free medical advice for ships at sea is now available through governmental and commercial coastal radio stations operated on the Atlantic and Pacific coasts of the United States.

On the Pacific coast, United States Marine Hospital No. 19, at San Francisco, Calif. (call letters KPH), has been designated to furnish this service.

Ships desiring medical advice can secure prompt service by addressing a radiogram to this hospital through any radio station with which communication is established, the radiogram to state briefly the symptoms of the person afflicted and to be signed by the master of the vessel.

The advice given by the hospital will be phrased in language (English) intelligible to the layman.

This free medical service has been established primarily for the benefit of ships not carrying physicians. However, should occasion require, consultations may be had by radio by ship's physicians with the hospital staff.

While the Panama Canal was not included in the original scheme, several requests for medical advice have been received here from ships at sea and have been given prompt attention.

UNITED STATES COAST GUARD STATIONS

Coast Guard stations included in this volume are maintained at the places named in the following table. The stations are manned continuously and are supplied with boats, wreck guns, beach apparatus, and all other appliances for affording assistance in case of shipwreck. Instructions to enable mariners to avail themselves fully of the assistance thus afforded will be found in the appendix, page 288.