Based up the City Slicker feat from Races of Destiny.
Sea Dog
You are familiar with the life of a sailor and the inner workings of a ship.
Benefit: Balance, Climb, Profession (sailor), and Swim are always class skills for you.
Special: This feat may only be taken at 1st level.
I'm pretty sure there is a feat like that in Stormwrack already.
That one is definitely not unbalanced.
Sounds like a reasonable feat to me.
Personally, I think feats like this cut too much into the skilled classes, Rogue particularly. Rogues already have enough problems.
What about Use Rope? I've never been a pirate, but in the movies everybody on sailing ships spends all their time playing with ropes. Is this subsumed in Profession (Sailor), which renders "Use Rope" useless for everything except tying people up?
Change Swim to Rope Use. Historically, most sailors didn't know how to swim, though knowing how to tie knots and use ropes was a necessity on board a ship.