Dead Reckoning by Surface Current Observation

Abstract

Recently an electromagnetic method for measuring the velocities of ocean currents for oceanographic purposes has been shown to be reliable enough for the observed velocity of the surface current to be taken into account in dead reckoning navigation in the open ocean. A preliminary test of the electromagnetic method as a navigational aid was made in 1949 on one cruise covering a distance of 1000 miles across the Gulf Stream and back. A total of 52 miles of lateral drift was corrected to produce a straight line of travel through the observed currents, and this correction enabled the ship to return to within 2 miles of the starting point. Seven less formal experiments performed in 1950 indicate that ordinarily, on straight-away courses, the lateral drift component caused by currents can be measured and corrected with the expectation that the undetected drift will be less than 1 percent of the distance travelled.