Must follow navigation rules for powerboats (and indeed any boats on the water), refers to the rules when approaching another watercraft while cruising. If another boat is attempting to cross you from the left (or port side), you have the right of way to maintain your speed and direction. If, however, they are on your right (starboard side), they have the right of way. This all changes if you are approaching a sailboat under sail (and not motor), in which case, they always have the right of way.