I just ordered up via ILL a piece of German scholarship which from the abstract seems to redate some early Roman coins (aes grave with a prow and the quadrigati) and connected them with the events of 241BC. I’ll reserve judgement on that until I see the article. However, it also reminded of this portion of Ovid’s Fasti, calendar of the Roman year in poetic form:
I spoke these words to the god [sc. Janus] who holds the key.
‘Indeed I’ve learned much: but why is there a ship’s figure
On one side of the copper As, a twin shape on the other?’
‘You might have recognised me in the double-image’,
He said, ‘if length of days had not worn the coin away.
The reason for the ship is that the god of the sickle
Wandering the globe, by ship, reached the Tuscan river.
I remember how Saturn was welcomed in this land:
Driven by Jupiter from the celestial regions.
From that day the people kept the title, Saturnian,
And the land was Latium, from the god’s hiding (latente) there.
But a pious posterity stamped a ship on the coin,
To commemorate the new god’s arrival.
I myself inhabited the ground on the left
Passed by sandy Tiber’s gentle waves.
Here, where Rome is now, uncut forest thrived,
And all this was pasture for scattered cattle.
My citadel was the hill the people of this age
Asses did stay in circulation for a very very long time and were minted very sporadically during the late Republic. Ovid’s Augustan age testimony provides evidence that worn base metal coins had become the norm but that the types were generally known. The prow however did not hold a particular meaning for a contemporary viewer. Ovid has the god explain that the prow commemorates Saturn’s arrival. This would have seemed plausible because Saturn was the god of the treasury, even if it is unlikely to have been the original inspiration. Crawford suggests the visual inspiration comes from this beautiful type of Antigonos Doson, c.227 BC (See RRC p. 42 esp. n. 5):
Naval imagery first appears on Roman coins, unsurprisingly, when they become more adept as a military power. And it has even been argued that naval imagery on aes signatum commemorated the very battle in which the bronze itself was captured in the form of rams, armor, and other spoils from the Carthaginian enemies. However awareness of symbolism slips away as particular images stop resonating with contemporary audience, hence Ovid’s deduced explanation.