They're using nautical directions.
Forward is towards the front of a ship, aft is to the rear. To complete a simple sub-set, port is left, starboard is right, when looking forward.
So they're at the railing nearest the front of the vessel.
There seems to be some debate as to whether that's exactly what he said, or that he pronounced it differently, or if that's what he meant. Here's a still from the movie, with the official subs on.
He says it quite clearly, exactly as written.
[I shrunk & saved a low-quality image for data-saving; other than that it's untouched. It's a dark scene.]