BEFORE THE present war, the average navigator seldom visited the high latitudes and rare indeed was the naval officer who had crossed the Arctic Circle. Since the arrival of U. S. troops in Iceland in 1941 this situation has radically changed and many men-of-war and merchant ships have penetrated into the Greenland and Barents Seas. The following "wrinkles," it is hoped, may be of assistance to those who may have to navigate these seas and who have not as yet ventured north of sixty.
Perhaps one of the first things that is noticed in heading north of sixty is that the sunrise and sunset tables in the Nautical Almanac end at 60°. This turns out to be a minor worry because the tide tables fortunately include a table of times of sunrise and sunset which extends to 76° north latitude. The moonrise and moonset tables also extend only to 60° north latitude. The only way to calculate the time of moonrise or moonset conveniently that was discovered was to compute it for 60° using the local longitude and then extrapolate the table to the local latitude. While not accurate, the result will generally be close enough for most navigational purposes.
There is a high percentage of overcast days north of 60°, and astronomical sights are taken whenever they are available, but during a large portion of the year the sun rises but a few degrees above the horizon even at noon, and north of the Arctic Circle, 66°-33’ north, at certain periods the sun does not rise at all. Again near the summer solstice, the stars are invisible for several weeks regardless of the weather. Authorities on navigation do not recommend sights of heavenly bodies below 15° altitude due to the refraction caused by the atmosphere, but in high latitudes the author had excellent success with sun sights as low as 5° above the horizon. On one occasion when in Denmark Strait, a sight had not been available for several days, during which time a heavy storm had been weathered. Due to currents, the dead-reckoning position was most uncertain. The skies cleared and sights were obtained about 9:00 A.M. with the sun at an altitude of 5° and the moon at an altitude of 9°. The resultant fix was plotted and a course set for Cape Bjargtanga, Iceland, which was picked up exactly on the predicted bearing a few hours later.
As stated above, star fixes are infrequent; a pale sun peeping through thin clouds is usually the only navigational sight available. When one does get a clear twilight and obtains sights of stars there are two precautions to observe. First, stars on northerly bearings may be on their lower transits, which is a little confusing the first time it is encountered; however, with the use of a time diagram the correct hour angle is easily determined and the sight solved accordingly. The other is that mirage on the horizon is frequent and this can easily throw the position off several miles. Mirage was often encountered at evening twilight, but never at morning twilight. Of course, mirage may be encountered in any latitude, but is more prevalent north of sixty.
As one goes farther north, other difficulties creep in. Dreisenstock's excellent tables do not extend north of 65°, but H.O. 214 is now available to 80°, while Ageton and the cosine-haversine methods are good in any latitudes likely to be encountered. The red and blue azimuth tables end at 70° north, but H.O. 66 (Arctic Azimuth Tables) is available, and Ageton is sufficiently accurate for azimuths at any latitude.
The magnetic compass is nearly useless around Iceland and in the Barents Sea due to the presence of magnetic disturbances. Therefore, dependence must be placed entirely in the gyrocompass. The farther north, however, the less the directive force of the gyro; also, the limit of the latitude correctors on most compasses is 70°. Therefore, when north of 70°, leave the latitude correctors set at 70°, take frequent azimuths, and using the error found as a deviation, set the true course accordingly. The maximum error encountered with the Sperry MK XI Mod 1 compass was 4° west in the latitude of 76° north; but the unfortunate part of gyro errors is that they are unpredictable, that is, they vary with the course and with the latitude, having been found the greatest when headed east or northeast, and least when headed south or southwest. In addition, due to the smaller directive force of the gyro, small mechanical defects or maladjustments which might cause negligible errors in low latitudes cause appreciable errors in the far North.
The latitude and longitude indicator combined with the dead-reckoning tracer also reads only to 70°. This problem was solved by pulling the switches on the latitude and longitude indicator but letting the tracking table run. By marking the table every half hour, a task usually delegated to the quartermaster of the watch, the run in course and distance can be picked off to scale and compared with the dead-reckoning plot on the chart or plotting sheet. Remember to apply the deviation of the gyrocompass when making the comparison. Keeping the tracking table running in this manner is considered most important as the constant zigzagging and possible changes in course and speed may make a large difference between the dead-reckoning predicted plot and what actually occurred.
The charts available, while not all that could be desired in accuracy, are considered adequate. However, the plotting sheet, 3,000p, from 65° to 70°, though usable, is of such large scale that it is awkward to handle, while plotting sheet 3,000q from 70° to 80° is of such small scale that it is worthless. What are needed are plotting sheets from 65° to 70°, from 70° to 75°, and from 75° to 80° with longitude 2 inches to the degree and latitude in proportion. Since such sheets were not available, the answer was to make a usable plotting sheet. This was not as difficult as it appeared. Taking the back of a low latitude plotting sheet and chart BA 2228 as a scale, a plotting sheet for latitudes 68° to 76° was constructed in a few hours and used with great success. .
The keeping of an accurate dead-reckoning plot is of greater importance in the high northern latitudes than in the more southern ones because of the sparsity of astronomical sights and also the absence of radio beacon stations. An accurate dead-reckoning tracer is of great value, but this fails to record the effects of wind and current. The instructions in the Current Tables Atlantic Coast (pp. 158— 161) as to how much to allow for wind and how to combine the wind with a known current were followed with remarkably accurate results.
No mention has been made of the subject of icebergs and field ice, nor of the storms and fogs encountered in the high latitudes. These are problems that must be solved as they occur, but the information concerning them in the sailing directions is invaluable and must be studied.
So to those about to sail north of sixty, “Good luck and happy landfalls.”