Because if you face the back of the boat the sides reverse. It’s similar to stage left. When you can’t afford to be confused, one name is better than a conflicting argument between your left and the boats left.
Do you own a car? Commonly when speaking with a mechanic they'll ask questions like Driver's side or Passenger's side to get away from left/right.
People very often describe things with just _left_ or just _right_. They don't say things like when I'm sitting in the car the door to my left is hard to open. They just say the left door is broken even when both them and the mechanic are facing the car head on.
By having people use an unambiguous vocabulary it makes up for people not thinking about how their statements will be interpreted. If the deckhands were genius's they're be charting the course not heaving rope.
You aren't wrong. In that mistakes can be made. But if I ask you about your left hand, is that ambiguous? By your definition here, that is an ambiguous question. But, that just feels wrong.
Edit: I'll note that it is amusing to compare to cars. It seems the etymology of the terms is literally "driver side".
It's not ambiguous because you have a directional reference built into the phrase and speaking directly to a singular person: "ask you about your left hand".
It is certainly clear if one would say "left facing stern" or "left facing aft", but that's a mouthful when you can just shorten it (and the reference facing direction is not relevant). Bonus points if the shortened version can't be mistaken for another direction...
BTW, I'm 100% down for introducing dedicated words for "my left", "your left" etc vs just "on the left". It would certainly save me a bit of time when my family asks me to look for something and they flip between the two meanings in the same sentence.
This still falls due to you having to have a point of reference for front of boat. See other threads where double ended ones do not have fixed starboard and port.
Reminds me of this book[0] about (air-cooled) VW maintenance, which goes right into how to tear down and rebuild the engine. Anyway, it can be disorienting, at the back of the car, looking at the engine and knowing what’s front/back, but I recall he wrote something like:
Now look at the front of the engine (FRONT IS FRONT) and you’ll see…
Also, happens to generally be one of the most beautiful to read and to look-at technical manuals I can think of. Right up there w The C Programming Language.
The problem is that people (especially in stressful situations when they’re not thinking carefully) will say things like “that one on the left!” and the person they’re talking to (who is often facing them and thus reversed) won’t think to ask “my left or yours?”
But if you train people to use specifically-invented unambiguous terms that can’t be screwed up, their brains will reach for those words when they’re in trouble.
What if you're addressing someone on a boat who's facing sideways? Or a group of people facing different directions? Or you can't see them and don't know which direction they're facing, and they don't know which direction you're facing?
