Quartermaster and Helmsman are the same thing. I suspect you are looking for the naval equivalent of the army QM. That's the purser. The other maritime specialists are Sailing Master, Carpenter and Sailmaker.
In the RN, Captain and Lieutenant are Commissioned Officers. Lieutenants in command of sloops are styled 'Master and Commander', and are entitled to the courtesy title (but not the pay or seniority) of Captain.
Sailing Master, Purser, Surgeon, and Midshipman are Warrant Officers.
Bos'un, Carpenter, Sailmaker, and Gunner, along with their Mates and Master's Mates are Petty Officers.
Quartermaster and Captain of the (Fore/Main/Mizzen) Top are senior Ratings, followed by Able Seaman, Ordinary Seaman, Landsman and Boy.
The Marines use army rank - Major, Captain, Lieutenant, Sergeant, Corporal, Marine (not Private or Soldier). A Marine Captain serving afloat has the courtesy title of 'Major' (to avoid confusion with that august being, The Captain).
In merchant vessels, things are a bit more amorphous. There will be a Master (sometimes referred to as Captain) and one or more Mates. These are the equivalent of the Navy's Commisioned and Warrant Officers. There will be the usual Petty Officers and Ratings (though in smaller numbers than in a naval vessel). There may also be a supercargo - the representative of the owner (or the owner himself). Most merchantmen would have very few landsmen and only one or two boys, and the specialists would be expected to help with sail-handling.
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