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Pacific influencing the weather (keyed in plain language). This bulletin is suitable for preparing weather maps at sea.

2. Local weather bulletins containing forecasts, storm warnings when issued, and a weather summary for specified areas of the Pacific coast and Alaska are broadcast on schedule every day by certain United States Naval or Coast Guard radio stations and (KSE), (KOK),. (KPH), (KFS), (KEK), and (KPK). Local weather information on request may be obtained from (WXH) Ketchikan, Alaska.

3. Storm warnings, in addition to being a part of the above bulletins (major and local), are broadcast by certain United States Naval radio stations, at the end of the first ensuing silent period (time of listening on distress wave) after the message has been received at the broadcasting station and every 2 hours thereafter for a period of 10 hours unless superseded. These warnings are broadcast in plain language and on the frequencies assigned to the service (maritime or aeronautical) to which they are destined.

Complete details relative to this service are published in Radio Circular No. 1, issued by the Weather Bureau, which, together with a card descriptive of storm warnings, may be obtained upon application to any United States Weather Bureau office. Details are also given in Hydrographic Office Publication No. 205, Radio Aids to Navigation. These publications give the schedules with times and frequencies of all broadcasts, together with tables for decoding as needed.

Storm warnings broadcast by commercial radio stations are generally transmitted on the hour or the half-hour at hourly intervals.

Scheduled broadcasts of weather information affecting the Pacific coast of the United States, Canada, and Alaska are also made by Canadian radio stations. Most of these stations supply weather informtion on request only and without charge. (See Hydrographic Publication No. 205, Radio Aids to Navigation.)

RADIO NAVIGATIONAL WARNINGS affecting the regions described in this volume are compiled by the United States Hydrographic Office, Navy Department, and by the Lighthouse Service, Department of Commerce. These warnings contain important information regarding derelicts, defects and changes to aids to navigation, mine fields, etc. They are broadcast by certain United States Naval Radio stations and Ketchikan (WXH), Alaska.

These broadcasts are divided into 3 classes: (1) Major and Secondary Hydrographic Broadcasts, (2) Local Hydrographic Broadcasts, (3) Emergency Hydrographic Broadcasts.

1. The major and secondary hydrographic broadcasts (Pacific) are sent out every day at 7:00 a. m. and 7:00 p. m. (Pacific Standard Time) by Mare Island station (NPG), San Francisco, Calif. The information broadcast affects the Pacific coast of the United States together with important Hawaiian Islands Notices. The content of this broadcast is usually adequate for offshore navigation; however, it is recommended that before nearing the coast, ships copy the local broadcasts of the area they are entering.

2. Local hydrographic broadcasts affect only the area in which the broadcasting stations are located and occasionally adjacent areas.

EMERGENCY BROADCASTS AND RADIOBEACONS

21

These broadcasts are made on schedule from the stations listed below for the following areas: San Diego, Calif. (NPL). from Latitude 30°00' N. to 35°00' N. San Francisco, Calif. (NPG). from Latitude 35°00' N. to 39°00' N. Eureka, Calif. (NPW).

from Latitude 39°00' N. to 42°00' N. Astoria, Oreg. (NPE)

from Latitude 42°00' N. to 47°00' N. Tatoosh, Wash. (NPD)-

north of Latitude 47°00' N. to and includinį

Straits of Juan de Fuca.
Puget Sound (Keyport), Wash. Vancouver and Queen Charlotte Sound.

(NPC).
Ketchikan, Alaska (WXH). --- Alaska.
Dutch Harbor, Unalaska (NPR)-. Alaska.

Canadian radio stations supply hydrographic information on request. See Radio Aids to Navigation (H. O. 205).

3. Emergency hydrographic broadcasts of an urgent nature are broadcast by certain United States Naval Radio Stations in the area affected at the end of the first ensuing silent period (time of listeni on Distress waves, see p. 15) and every 2 hours thereafter for a period of 10 hours unless superseded. If the warning is of sufficient importance they may be broadcast by San Francisco Mare Island), Calif. (NPG) as a part of the regular major and secondary broadcasts in addition to the broadcast by the local stations.

A naval radio station is operated at Dutch Harbor (NPR). Practically all the canneries operate radio stations during the summer, and there a re several stations operated by other Government bureaus.

The Signal Corps, United States Army (see Communication, p. 6), operates radio stations at the following places : WXE-Anchorage.

WXW-Kotzebue. WXU-Cordova.

WXY—Nome. WXB-Point Barrow.

WXF-Kodiak. WXR—Seward.

WXK-Kanakanak. Radio stations of the Navy and Coast Guard can be identified easily by their call letters which always begin with the letter N.

RADIOBEACONS, installed at light stations and in lightships, are radio transmitters from which characteristic radio signals are sent out in all directions. A radio direction finder (radio compass) is a special radio receiver with a rotating coil antenna by means of which bearings are taken on radiobeacons or on any other stations sending radio signals.

It should be understood that the use of radiobeacons is limited to vessels equipped with radio direction-finders (radio compasses); on the other hand, radio direction-finder stations (see p. 23) can furnish bearings to a vessel if equipped only with the regular radio transmitting and receiving set.

The Lighthouse Service operates a system of radiobeacons, established along the coast. This system has recently been coordinated with that of the Lighthouse Administration of Canada in order that the methods of operating the radiobeacon system of the United States and Canada might become more effective. In order to facilitate the widest utilization of this system of navigational aids, there are issued at intervals radiobeacon charts, upon which the radiobeacons are shown, with their characteristics and operating schedules. These charts may be obtained free from the offices of the District Lighthouse Superintendents.

All radiobeacons operate during fog or low visibility; also in clear weather during scheduled intervals. The clear weather schedules and other details are given in the Light Lists, Hydrographic Office Publication No. 205, and other radio publications (p. 26). Changes are announced in the Notices to Mariners.

The radiobeacons in or near the area covered by this volume are given in the following table:

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NOTE.—St. Paul Island is operated during fog and low visibility, only upon advance request made to (NPR) Dutch Harbor. From May 1 to November 1, the radiobeacon operates regularly during the second and fifth 10 minutes of every hour.

Originally radiobeacons were intended only for fog signals, but they have proven to be useful for clear-weather navigation as well, because of their considerable range. For this reason they are operated at certain periods in clear weather. This also facilitates the calibration of radio compasses on board ship, see below. The use of radiobeacons will greatly reduce the dangers incident to navigation in a fog, but this should not cause the mariner to neglect other precautions such as the use of the fathometer or lead.

The bearing of the radiobeacon may be determined with an accuracy of approximately 2o 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 with the knowledge of the telegraph code. The radio direction-finding apparatus (radio compass) consists of a radio receiving set, similar in operation to those used for radiotelegraph or radiotelephone 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 or indicated instrumentally 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 the magnetic compass. Those using radio direction-finding apparatus aboard ship are cautioned to bear these errors in mind and to keep the radio direction-finder (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. At some of the stations special radio and sound signals are synchronized for distance-finding purposes.

RADIO BEARINGS

23 A general description of this method of navigation and the instruments required is given in the Lighthouse Service publication Radiobeacons and Radiobeacon Navigation, which may be obtained from the Superintendent of Documents, Government Printing Office, Washington, D. C., for 15 cents. Bureau of Standards Scientific Paper No. 428, The Radio Direction Finder and Its Application to Navigation, may be obtained from the same source for 15 cents.

Vessels are requested to forward reports to the Commissioner of Lighthouses, Washington, D. C., or to the Superintendent of Lighthouses, Ketchikan, Alaska, as to the effectiveness of radiobeacons.

Radio bearings from other vessels.—Any vessel equipped with a radio direction finder can give a bearing to a vessel equipped with a radio transmitter and receiver. Such service will generally be furnished when requested, particularly by Government vessels. These bearings, however, should be used only as a check, as comparatively large errors may be introduced by local conditions surrounding the radio direction finder unless known and accounted for.

Any radio station, the position of the transmitter of which is definitely known, may serve as a radio beacon for vessels equipped with a radio direction finder. Canneries maintain radio stations and the Army has a net work of stations throughout Alaska. However, mariners are cautioned that stations established especially to give radio bearings for maritime service are more reliable and safer for use by the mariner, for numerous reasons. The geographic positions of commercial radio stations listed in various publications, generally, are only approximately given.

Many navigators are using the ship's radio direction-finder as a help in avoiding collision in fog, detecting with it the presence and observing the direction of approaching vessels.

RADIO DIRECTION-FINDER STATIONS, established and operated by the United State Navy, will furnish radio bearings to 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 fathometer, 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 cannot 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 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.

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 kilocycles (800 m). When so used, the position of the radio direction-finder station transmitter is used in plotting the bearing.

There is no naval radio direction-finder station open to the public within the approximate limits of this volume.

For further details regarding radio direction-finder stations see Hydrographic Office Publication No. 205.

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 a Mercator 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 25 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 radio direction-finder station receiver or transmitter 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 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 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.

Should the position by dead reckoning differ greatly from the true position of the ship as determined by plotting the corrected radio bearings, a retrial should be made, using the new value as the position of the ship.

When the bearing is from a radio direction-finder station shore, the sign of the correction will be reversed to that given when the bearing is taken from the ship, and the position of the radio direction-finder station receiver is used in plotting the bearing.

Example.A ship in latitude 39°50' N., longitude 67°35' W., by dead reckoning, obtains a radio bearing of 2990 true on the radiobeacon located in latitude 40°37' N., and longitude 69°37' W.

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