Due to present war-time conditions, naval personnel should be at all times prepared to navigate life rafts or lifeboats with minimum equipment and tabular data. The Solan “Life-raft Navigator” (see illustration) is offered as the basis of a standard system of life-raft navigation.
The Solan “Life-raft Navigator” provides in convenient form, on a small waterproof card, all the astronomical data and formulas necessary to determine latitude and longitude with only a watch set to Greenwich civil time. The system is based on the theory that a body observed on the local meridian will give the observer’s latitude and longitude assuming the body’s Greenwich hour angle to be the longitude of the observer.
On one side of the card is printed a star chart of the 22 stars used in the system and Polaris. Outside the chart is printed a protractor which is to be used to measure the angle of celestial bodies in the absence of sufficient material on hand to construct a larger instrument.
On the other side of the card is printed the name, declination, and right ascension of each of the 22 stars. A table of sines, and RAMS+12h for the first day of each month, with the daily difference of 4 minutes noted to facilitate interpolation, the latitude formula, and the GHA* formula are also printed. The formula declination Sun = 23.5Xsine number days nearest March 22 or September 22, also printed on the card, was taken from an article “Navigation by Guess and by God,” by W. J. Luyton published on the back of H.O. Chart No. 2601.
Due to the inaccuracy of standard commercial watches, the correction for time past 0 hours GCT, Table VI, Nautical Almanac, was omitted from the GHA* formula. This omission will cause an error of approximately 1 degree in longitude in extreme cases if the watch rate is known.
The following examples, illustrating the use of formulas and tables, are printed on the card: On January 1, 0630 GCT, Aldebaran was observed S on meridian at 65.2°, Lat. = 24.8+16.4 = 41.2° N.; GHA = 0630 +0639-0433 = 0836 W. At 0650, Polaris was observed at 41°, Lat. = 41°. At 0710 GCT, Rigel was observed S on meridian at 40.8°, Lat.=49.2 — 08.3 = 40.9° N.; GHA = 0710+0639-0512 = 0837 W.: 0650 position = 41.0° N., 129.1° W. On January 2 sun was observed at 25°, dec. sun = sine 80X23.5 = 23.1 S, Lat. = 65° — 23.1 = 41.9° N. By checking with the Air Almanac (1943), the GHA of the 0650 local meridian is found to be 129.5°.
The star chart, in addition to being used to identify stars, may be also used in determining positions, for example: On May 3, 0100 GCT, a star observed in the zenith is identified as Sirius. GHA* = 0100+1440 -0643 = 0857, Long. = 134.3° W. Since the observer’s latitude is equal to the declination of a star in the zenith, the 0100 position is 16.6° S, 134.3° W. By checking with the Nautical Almanac (1943), the GHA of Sirius at 0100 GCT May 3 is found to be 134.4°.