I have always been suspicious of the "sudden" transition of the Romans to seapower. I actually suspect this is another area where their allies helped make up the difference; the Romans might not have been a very naval people, but they had a number of Greek allies in Southern Italy and Etruscan allies in Northern Italy who were and who could supply the technical knowledge and shipbuilding techniques that the Romans didn't have. However, this isn't an interpretation that shows the Romans as the best most adaptable awesome people who could reverse engineer any ship and become masters of any craft.
What do you think all the Metics in Eretria Eskhata are doing?The majority of them are tenant laborers and form Eretria Eskhata's peasant class, while some of the other ones are more urban craftsmen or merchants.
Yeah, I am pretty sure that we have mentions of Rome and especially its allies doing quite a bit on the sea before the whole conflict with Carthage really started. Plus they clearly recognized the usefulness of sea-trade since I think quite a few of their early conflicts and expansion was focused on that.