Port to port - Whilst the general rule is pass ’port to port’ (i.e. to the right), there may be situations where it is safer not to do this - eg passing in a lock pound when one boat has got seriously out of position, where the lock or bridge is at a difficult angle, or where one boat is preparing to moor.
Watch out for situations to pass ‘wrong side’ and indicate your intention by using the recognised sound signal (two blasts on the horn). Many experienced boaters are not familiar with sound signals, and it would do no harm if they were to learn! If you do overtake, generally do so on the left. Remember to allow for larger craft. The wider or longer a boat is the more room and time it needs to manoeuvre, especially at bridges, on sharp bends and at locks or moorings.