The Barbarian's Unarmored Defense explicitly includes shield benefits, whereas the Monk's version (despite having the same name) explicitly excludes it, so the answer is "depends on which class gave you the feature."
[MENTION=6841015]laughinggas[/MENTION]
I could see a shield (fluffed as a buckler) + sword (fluffed as a clutlass) working out alright. On the other hand, if you can persuade your DM to let you use the Mariner Fighting Style from UA (technically, it's only given to Fighters, Paladins, and Rangers, but it's also playtest stuff, so...) then that would be even better and would mesh very well with your concept: "As long as you are not wearing heavy armor or using a shield, you have a swimming speed and a climbing speed equal to your normal speed, and you gain a +1 bonus AC." That gives you half the benefit of a shield, lets you use a big two-handed weapon (I'd, again, fluff it as some kind of heavy cutlass), and ties more closely with your Barbarian-Pirate theme. Having a natural AC of 10+Dex+Con+1 with your stats, and being a Half-Orc, you'd get (presumably) AC 19 which is damned impressive at level 4. It's nice for if you have actual aquatic situations, since Unarmored Movement theoretically improves your swim speed indirectly.
As sated, you'd have terrible mental scores...but those sky-high physical scores, plus being a Barbarian, will make you a nasty force whenever it's time to throw down. And even when it's not, you'll be extremely sneaky (great dex, no armor penalties), acrobatic, and strong--all potentially very useful in the right kind of campaign. The Barbarian skill list kinda stinks, though, so you might also want to talk about a slightly tweaked Pirate background (e.g. trading the redundant Athletics for Intimidate, since the Pirate alternate feature is *specifically* about intimidating people and such.)
