NavList:

Yeah, it's kind of strange that the assumption is that the Navigator on an offshore voyage will use "local" time (constantly adjusted, of course, as the ship makes easting or westing) rather than simply keeping his chronometer set to GMT.   I assume these are customs derived from naval tradition, similar to the one of reporting ship's position to the captain at 0800, 1200, and 2000.  Why 4 hours before noon but eight hours afterwards?   Why exactly 1200 rather than 1300, after the navigator has had time to reduce a meridian transit sight, giving both an excellent latitude and a longitude from an advanced morning sun line?

I've just finished teaching the Power Squadron's Junior Navigation (basic celestial) class.  They could be a little clearer, but the implication is clearly that at sea ship's clock time is purely based on longitude, while when on shore ZD is based on civil time including any change required due to daylight time.   One, in fact, does not have to look to daylight time to see an example of civil ZD not agreeing with "sea time"   US time zones stretch considerably farther west than their correct zonal boundaries -- for example, the US's Eastern time zone (ZD +5 "standard" time) extends to approximately Lo 87 W and its Central time zone (ZD +6) past the central meridian of ZD +7,  Lo 105 W!