They apparently also used small ships or is this just an artistic freedom to not to have to paint the full size? (Other than that I would love to have such small rowboats in. For landing on shallow coasts for example. And it would look nice. We could even have them on lakes.) Those are from the Sarazzins' invasion on Crete (820AD): I think a generic one could fit our needs. We don't really need one for every culture as long as they not as different as e.g. those of Venice were. (so for Venice we probably needed different rowboats. The decision is up to our artists.) Also tell me, if you think this kind of small ship is superfluous (or we just scale down a big ship, but this would look mysterious).