We all know the rule that port tack boats must keep clear of starboard tack boats, ( see Rule 10 below). In this example we will take a look at a situation that can occur, and can cause a protest which should never happen.
Rule 10: On Opposite Tacks
When boats are on opposite tacks, a port-tack boat shall keep clear of a starboard-tack boat.
If a port tack boat has the lead and can be clear a head of the starboard tack boat, there are no problems. If a port tack boat is not going to clear a starboard tack boat, the port tack can, either alter course, and sail below the stern of the starboard boat, or tack away to starboard and keep clear.
It is a wise idea for the starboard boat to call for 'starboard' to notify the approaching port tack boat. This gives the port tack boat fair warning to stay clear. There is one incident where the starboard tack boat can get into trouble. If the starboard tack boat alters course and hits the port tack boat, see Rule 16 below.
Rule 16: Changing Course
When a right-of-way boat changes course, she shall give the other boat room to keep clear.
As in Figure 1, both boats are on a straightforward course, with the red port tack boat being clear ahead at the cross. In this situation, the blue starboard tack boat alters course, and sails into the port tack boat. The starboard tack boat may think it is the right-of-way boat, and has rights, it does not.
The blue starboard tack boat must give room to red boat to keep clear, here it did not. The red port tack boat does not have a chance to keep clear, and is not able to react to blue's course change.
Now this does not mean the Rule 16 stops any boat on starboard tack from altering course. A starboard boat can alter course so long she allows the port tack boat to keep clear. Just be sure if you are the right-of-way boat, call 'starboard' to give clear warning, and if you are going to alter course, which is your right, give the other boat room to keep clear.