why is starboard called starboard?

I'd been taught Ju52's reason except that starboard was translated from Norse, but again meaning steerage board (rudder, but placed on the boat's side). If you put that side of the boat to the port you'll go nowhere, hense the other side becoming the Port side.

Funny Story

I make monkey-fist earrings (in red and green for port and starboard, of course) and sell 'em at boat shows, fishing equipment shows and the like, wherein you might expect the denizens to be somewhat knowledgeable as to the significance of "Left Port Red" ... but, au contraire, mes amis....

At a rather prestigious show recently I had a simply delightful piece of "arm-candy" come up and spend a few minutes staring at the displays with a very pretty little moue of confusion upon her porcelain face...

After a few moments, she finally asked me if I was aware that my earrings were mismatched on the display, upon which an older and somewhat saltier lady tapped her on the shoulder and pronounced: "My Deah, you are a lovely thing, but do, PLEASE, stay OFF the water!"

Port & Starboard

the way i have heard it:
Port is beacuse in the old sailing days, no engines, the vessel was always discharged and lodaded on the same side - port, which happended to be opposit to the steering board - starboard.

to add a little bit more to the discusion, this is how the COLREg's have been structured. All vessels were sailed in such a manner so they were protecting their steering board - which was on the starboard.

This point still makes a lot of confusion.
Ships cross at red lights, funny, seems the green the 'go', but it is not. It is contrary the automobile way of thinking, but the water roads are in same way of car roads, with the light different what we commonly imagine to the traffic lights, so the confusion. By shipping the red is the 'go' and indicates the direction of ship as well. The green is the safe border side to coast.

In Portuguese the terms are:

Portside = bombordo, which means the 'good' side to load at board, today does not matter anymore.
Starboard = estibordo, a mere translation of the term in the way of spelling.

Strangely today we see most ships docking at steerboard, at the green light in ports, because the steer is in middle now, not so much important, the safest for carrying load. It is just the running important now. So it should not be called 'Port'side anymore, something more like Leftboard and Rightboard would be easier. Or Crossboard and Starboard. Or Dangerousside and Freeside. The terms should have been updated to avoid confusion nowadays for new commers. But are common terms in industry, then this won't happen.

Unless I'm misunderstanding what you wrote, ships don't "cross at red lights". If you're looking at a ships red (portside) nav light you're the give-way vessel. When I teach new boaters I call it "the stop light principle. If you see the red nav light, stop or go around his stern".

Yes, you missunderstood. I did not mean 'giving pass' to the right ship coming, the rule is the same for cars in germany, who comes at right has preference. So the other ship wait and turn around the right commer stern. What i meant are ships in different directions like common happen in river up & down, here in Elbe for example. Ships goes at 'right lane' and the faster also pass at left side. So the red lamp is the left crossing side of both ships. However, for sure we all learned a lot in this thread, also the experts.

French comment

Babord and tribord

If written on the ships back give Batri, like battery...

This was mnemotechnically how new sailors were taught centuries ago already in France