The Veneti as described in Julius Caesar's Gallic Wars had large seafaring ships that were described as taller than typical Roman ships, with high gunwales, which sounds to me almost like the ships of the late Medieval period. Do we have any hard evidence about the design of these ships, and if they were in fact comparatively advanced, the range of the Veneti's travels?
Do we know if the Veneti's shipbuilding technology or maritime culture survived the brutal invasion by Caesar, and if their seafaring continued afterwards? If so, did they influence later antiquity?
More could be said, but you might might find an answer in this previous post.
Along with Caesar's description, the best archeological evidence at hand are the remains of the carvel-built "Romano-Celtic" vessels found along the coast of the Channel (Blackfriars, Guernesey, Tardinghen, etc.), : there's a strong argument to be made in favour of it being evolved from the pre-Roman vessels in the Atlantic and Channel, sharing same broad characteristics found in De Bello Gallico and same broad trade function, without these being similar as indigenous elements would have been largely transformed under Roman influences (broader use of iron, Mediterranean gunwales in some ships, etc.).
Due to their probable build, but as well the nature of maritime relations of Veneti, it's really unlikely they were ever able to go in high-seas or much beyond the Channel.