[notatoad]

it's unambiguous if you know you're talking about direction relative to the boat, but you don't know that you're talking about direction relative to the boat.

your left hand is still your left hand, even if it's on the starboard side of the boat. you always need some additional disambiguation to specify that you're talking about the boat. i've never sailed a boat with slavic people, but i'm guessing they use a phrase like "boat left" and "boat right", not just "left" or "right".

also, i've never heard anybody describe a riverbank as "left" or "right". riverbanks would be described by their cardinal direction, like the "east bank" or the "south bank"

[mr_toad]

The left bank of the Seine is quite iconic!

https://en.wikipedia.org/wiki/Rive_Gauche