A helmsman is the person who steers a ship.
Rank and Duties
In the Royal Navy, a helmsman typically holds the rank of quartermaster and may have navigational duties as well. However, the main task of a helmsman is to execute orders given to him and therefore, the helmsman himself may not necessarily be capable of navigating the ship.
Aboard the Obra Dinn
The Obra Dinn carried only one member of the crew listed as helmsman in the crew manifest, an Englishman by the name of Finley Dalton. It can be assumed that at least two more people were capable of taking her helm, though, as the helmsman, like any other watchstander, would have to be regularly relieved. This is further supported, as when Dalton perished, the ship still managed to hold a steady course while its crew was alive. Dalton did not survive the voyage.