NavList:

A Lunar skeptic mentioned John Karl's book, "Celestial Navigation in the age of GPS". Chapter 8 devoted to Lunars.  Specifically the Lunar skeptic quoted Karl as saying Lunars gives 2 minute UTC certainty.  I read the chapter, and on page 96 he lists the following problems and their accuracy cost and then converts the 2 minutes UTC certainty to Longitude certainty 30'.

(1). NA is in accurate for coordinates of the moon = .3', oblateness of earth can account to .2' error.  Perfectly adjusted sextants have .15 to .33' of arc error depending on quality of sextant.

(2). sights at sea are expected to be within 1' to 3' depending on conditions and observer's skill.   

That's how he came up with 2 minutes UTC certainty.   And then Karl considers earth rotates 1' in 4 sec, the 120 sec uncertainty in UT makes Longitude certainty to be 30'!

On the other hand, I read a statement Slocum made about his Lunars (source "The Lunar Distance Method in the 19th Century.  A simulation of Joshua Slocum's observation on June 16, 1896",  author Siebren Y. van der Werf).  ...."her (lunars) longitude agreed within five miles of that by dead-reckoning".  Not too bad.  Not fantastic.  But certainly better than being off by 30' of Longitude that John Karl predicts.   PLUS Joshua only took 3 sights (Sun Altitude, Moon Altitude, LD Sun-Moon).  No run of sights, no averaging the sights.

What was the accuracy experience during the Age of Sail when they used Lunars to derive UTC?   I'd assume the Navigator had a Good Sextant (for the time) and was skilled.   And he/she was taking sights onboard a ship (and not on land).  I'm curious what accuracy a navigator on a 35 foot offshore sailboat can achieve? 

Thanks, Bob B