Although my expertise lies with Italy between the 10th and 14th centuries, I think I can shed some insight on a common misconception about pre-modern navigation: figuring out position via constellations would be best done by beaching the boat and taking measurements ashore. In this thread from a few months ago, u/XenophonTheAthenian explained:

I believe Casson says that triremes had to beach at night. I don't think I've actually seen any dispute about that to tell the truth--Thucydides outright tells us that warships beached at night and during meals. It was something of a necessity, as warships were built purely for speed. They had no quarters and no room for provisions. It's possible that larger warships might not have had to stop every night, and under certain circumstances, especially in very long journeys, we don't hear of the ships being beached at night, but I think the texts are quite clear about this

Now, I know the thread is principally referring to warships, not mercantile ships. However what I can add is that as late as the tenth-century, Venetians (who were primarily commercial navigators; Venetian war fleets consisted mostly of commandeered merchant ships) developed a system of outposts between Venice and Constantinople that were precisely one day's travel from each other. In fact, stopping overnight continued to be the preferable way of traveling until the adoption of Atlantic shipbuilding techniques in the Mediterranean.

(P.S. I had a convenient PDF of travel times between Venetian colonies but obviously, now that I need it I can't find it.)