The German term Bootsmann translates to Boatswain, i.e. the senior crewman of the deck department.
In a military context, Bootsmann (Btsm or B) is the lowest Portepeeunteroffizier (NCO with portepeé) rank in the German Navy. It belongs to the particular rank group Senior NCOs with port épée. It is grouped as OR6 in NATO, equivalent to Petty Officer First Class in the US Navy, and to Petty Officer in the British Royal Navy.
In navy context NCOs of this rank were formally addressed as Herr Bootsmann also informally / short Bootsmann.
The sequence of ranks (top-down approach) in that particular group is as follows:
Unteroffiziere mit Portepee
The abbreviation "OR" stands for "Other Ranks / fr: sous-officiers et militaires du rang / ru:другие ранги, кроме офицероф"!
These names were adopted for the Russian Navy as боцман and боцманмат by Peter the Great, among many other Prussian and Holland military ranks; they were initially treated as positions rather than ranks.