NavList:

Hello Lars,

Although the previous assumption about the CMG / SMG (200° / 6 kts) was a bit off, it was nonetheless not that far from the Logbook data (241° / 5.25 kts probably for Surface Speed). This did not "spoil" too much our previously published Fix ( 23h31m02s UT : N30°42.7'/W014°47.7' ) which accordingly can be slightly improved here-after with the Logbook data themselves.

Port tack ? Starboard tack ? Given their location just north of the Canary Islands, Barque Prompt might have already enjoyed downwind sailing - it would be interesting to know the wind direction - although the bottom speed seems a bit low, unless she were undersail (all sails rigged ?) already heavily loaded (heavy ballast and/or other goods ???), which are all points which would be interesting to know too.

Nonetheless, if we run again our example with SMG/CMG at 5.25kts/241° with UT23h14m10s/Altair/67°57.5' and UT23h31m02s/Moon/20°12.5' on Aug 14th, 1908 we get the following slightly improved "best guess" Fix:

UT23h14m10s N30°43.6'/W014°47.3' (with Altair observed at Azimuth180.4° and the Moon at Azimuth 109.0°).

This latter result is even closer from the Captain's fix at N30°44'/W014°46.7'

Like you, I think that the Captain was smart enough to secure a clever Latitude LOP first, most probably through the observed culmination of ALTAIR which did not require the Chronometer. Hence this observation was likely performed at an actual ALTAIR azimuth probably slightly past 180°.

Then, with a bottom speed south component of only 2.3 kts the Captain could safely and not too uncomfortably feel like he could wait during some delay to observe the Moon, which could have been playing hide and seek amidst the clouds. So I am not surprised at all with up to a 17 minute delay between both observations. It was certainly important to him to also secure a reliable Longitude - the hardest coordinate to obtain - since the Canary Islands were coming closer and - possibly ? - could have been reached during night time only ... So he was quite clever through having secured a quite reliable fix in that respect.

Anyway, this is a very interesting example of Celnav with a very clever Star Latitude LOP which could be shot over only over a few minute time span (10 minutes at the most with nights coming quick at such latitudes in summer).

Attaboy to you, Captain Hugo Lundqvist !

Thanks again to you Lars,

Kermit