A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Roger W. Sinnott
Date: 2017 Dec 11, 14:41 -0500
Greg and Don,
The crew of the Essex did face navigation challenges -- prevailing wind and ocean currents being the main constraints. But I still think their choices would have been expanded if they could have used the lunar-distance method. (The Philbrick book is silent as to whether they had a current nautical almanac. But Capt. Pollard did take sun sights for latitude, so I suppose they did.) Their makeshift sails (each boat had two spritsails and a jib) gave them course-setting options.
Latitude sailing wouldn't be the shortest distance between two points, but it did offer two advantages: (1) You didn't need to know your own longitude well, and (2) you didn't need to know the destination's longitude well either. So you were likely to find an island even if its longitude in Bowditch was off.
On Dec. 20, 1820, when they spotted land, they thought it was Ducie Island but we now know it was Henderson, 70 miles farther west. So that's one mistake lunars could have avoided.