A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: John Clements
Date: 2020 Dec 29, 13:01 -0800
As it happens, my father (Robert M. Clements) is a Latin teacher. His reply to my version of this question:
Argo (a Greek word) was absorbed into Latin as a fourth declension noun, perhaps because ship names were all fourth? That's a guess. But tree names (quercus, pinus, etc.) are all fourth, and ships are made of wood… A bad guess, probably. But it is fourth, and the genitive in the 4th ends is ūs. That line is a macron. Does that help? It would indeed make the genitive Argūs navis, of the ship Argo.
So that's the typographical piece of the question, anyhow.