NavList:

From the 18th and 19th century logbooks I've studied (only a sample of the thousands out there), I've noticed a pattern. Lunars (lunar distance sights) were never a primary method of navigation for American commercial vessels. There was no "lunars era" comparable to the "chronometer era". Rather the primary method of determining longitude until the 1830s or so was dead reckoning, as it had been for centuries. Around 1830, the primary method began to switch over to chronometers. During the early period of lunars, from c.1770 to c.1830, lunars were used as an occasional check on the dead reckoning. In their logbooks, navigators only occasionally updated their dead reckoning with results from their lunars observations. Rather, they continued their dead reckoning until they were able to take a new departure from a point of land with results of lunars listed marginally. The "mindset" was centered on the dead reckoning. After c.1830 (and it is a decades long process of transition), the primary longitude listed in the logbooks become "long by chrono" with occasional checks by lunars.

 

For an example of a late holdover, take a look at the logbook of the bark "Mary & Louisa" from 1858 in the collection of the library at Mystic Seaport (mysticseaport.org). The navigator on this voyage from the northeast US to Shanghai uses dead reckoning as his primary longitude and for him the chronometer longitude is only a sanity check, listed once in a rare while (no lunars either).

 

I think I ought to risk stating the obvious here. Every navigator works in a unique manner. Many navigators in the 19th century never used lunars at all --except "in the classroom". Some others, unusual navigators, apparently did treat lunars as their primary method of finding longitude. But the only case I'm aware of personally is Nathaniel Bowditch himself. Additionally, I should note that the comments above refer specifically to "American commercial vessels".

 

Any thoughts?