Just for the record I never want to see a dagger coming at me. It is not safe in the hands of 90% of the people who use it...somewhat having to do with the fact that 98% of the people who could won't.
As for shields not making sense for the sea-faring types...well consider your time period. The pinacle "marine" of the approximate age was the Viking. They were not swashbucklers or fencers. Those crazies did not show up till gunpoweder so yes, shields make sense. Chain mail makes sense. Learning how to stay on your boat makes sense. Falling off and climbing back on board after the funny prank...that is crazy.
So ultimately do what you want. It takes the smallest bit of will to make it make sense for your character so you the paying customer can hve your enjoyment.
Joe S.