[MENTION=23484]Kobold Stew[/MENTION] Is there overlap between Gentlemen Jim and Katarina? Yes obviously. Does that invalidate Jim? No, absolutely not. Certainly not story-wise, but not mechanics-wise either. Here's why:
1. Combat Effectiveness - In melee I'd say he's slightly more effective overall as [MENTION=6781406]Unsung[/MENTION] points out thanks to higher HP and Second Wind, and maneuvers. This will only continue to grow with more extra attacks at 5th, and more feat/ability boosts at 6th, and on. Katarina probably does better targeted damage with advantage, but Jim has more staying power, more flexibility (sword n pistol & maneuvers), and can throw down some serious damage as well.
2. Inspiring Leader - This feat is a game changer, and before naval battles (where 10 minutes is easy to find) you are granting the party (or crew) a total of 42 temporary hit points!!! That is huge niche that could sway the tide of a naval battle - 42 temporary hit points to the crew is significant, and it gets better as you level! Plus the role playing potential is thru the roof! And keeps Jim in the running for Captain, if you so wish.
3. Forgery - Jim can do something no one else on the team can do: forge official papers and personal letters. Letters of Marque? Arrest warrants? Letters decommissioning a governor's rule from the colonial power? Decrees to pardon pirates from the governor's office? Issues from the constable for prisoner transfers? Commodore's orders to let your ship past a naval blockade? Yes, sir! Play this up and it's an awesome niche limited only by your imagination!
While I agree that Katarina may be a better overall candidate as Captain (due to her backstory and higher Sway), Jim could fit any of these other ship roles (in addition to being a Gunner in combat) and carve his niche there:
[sblock=Boatswain]Boatswain: The boatswain directly oversees crew on deck, makes decisions about how best to apply the crew's numbers toward the captain's orders, and directly reports on the state of the ship (physically and morale-wise) to the captain. The boatswain player handles all non-combat rolls involving the crew, such as ability checks, morale checks, and saves.[/sblock]
[sblock=Sailing Master]Sailing Master: The sailing master (a Lieutenant on naval ships) is in charge of navigation, identifying safe harbors and potential hazards on maps, and managing the sails (deciding how much sail to let out, how to orient the sails to the wind, and when to take down the sails). The player determines the ship's speed, makes any checks relating to the sails, calculates travel time, and should be passingly familiar with common sailing concepts (like how bearing and amount of sial exposed to wind influence speed). Check out
http://www.sea-distances.org/ for a great tool for estimating travel times by sail.[/sblock]
[sblock="Reserve Captain"]"Reserve Captain": Katarina is Chaotic Neutral, so you know it's only a matter of time before she splits the party or gets into trouble that indisposes her to fulfilling her role as Captain

When that happens, you could have an agreement as First Mate to "inherit" the Captaincy till her return (rather than the Quartermaster as is customary). As First Mate you'd take time at the helm and perform a jack-of-all-trades role on ship, tending sails here, lending a hand to the crew there, jumping in wherever you see the need.[/sblock]