“The accepted practice in a right-to-right passing situation in open waters is for both ships to turn to their right early enough to execute the usual port-to-port passing. It is only when the two ships are so far to the right of one another that it would be dangerous to attempt to cross over for a port-to-port passing, that the starboard-to-starboard passing is acceptable. And then, the law courts have held, the ships must pass on”