sjóliði,
this Type of axe-adze combination is one of the most ancient,and "boarding axe",Pulaski,and any number of other specialised tools descent from thence.
The idea is to cut in two directions without having to shift your position,a method useful in many tasks,usually something agricultural,but also in mining(either digging or building supports),roadwork,or in you name it kind of task,including the boarding of a sailing vessel in a rude,uninvited manner
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If i had to guess,i'd place it's origin in Iberian penninsula somewhere,a Portuguese orchardman's axe or the like.Vinyard or olive grove cultivation,some tough fibrous roots and rocky soils,judging by an ample volume inside the eye.
(The guy in the video is a trip:Such great tools,and obviously the skills to go along with those,and all coupled with imagination apparently addled by video-games,or comic books,or some exotic TV programs...Quite solidly divorced from any reality known to me,in any case!