Let’s look at what the rule says:
When an inside overlapped right-of-way boat must gybe at a mark to sail her proper course, until she gybes she shall sail no farther from the mark than needed to sail that course. Rule 18.4 does not apply at a gate mark.
After tackling the other sections of Rule 18, you will find that Rule 18.4 is pretty straightforward.
In essence, an inside boat is not allowed to push the outside boat that is overlapped any further from her proper course than necessary. The inside boat must keep to her proper course. Remember…
Proper Course A course a boat would choose in order to sail the course and finish as soon as possible in the absence of the other boats referred to in the rule using the term. A boat has no proper course before her starting signal.
So in example 1, we can see that yellow gybes as soon as it is feasible to do so which will take her on a course to the next leeward mark; her proper course…
If yellow at position 3 did not gybe but ventured further out, she would break Rule 18.4.
The second sentence in Rule 18.4 states simply that:
Rule 18.4 does not apply at a gate mark.
This can be illustrated in example 2 below. Rule 18.4 does not apply because the boats move through a gate mark. At position 2, yellow can decide if she wants to continue on her current course and round the east mark or gybe and round the west mark. Blue, as the windward boat has little to say about it because she needs to keep clear of yellow under Rule 11.
At position 3, yellow is in the zone and there is an overlap so Rule 18.2(b) applies.
Let’s have a look at the below events. Blue requires to keep clear of yellow as the windward boat. At position 4, blue is getting frustrated because she wants to gybe and go around the mark. However, yellow stays on her course to achieve a tactical advantage and regain the lead.
Gate marks are popular in larger fleets as they break up the course and open up technical ingenuity among sailors.
The below scenario is not uncommon and could indeed involve many more boats. However, for the sake of familiarisation, have a look and see if we can sort out the traffic using Rule 18.
So to sum up Rule 18.4…
- It does not apply to “gate marks”.
- You can not sail any further than your proper course allows; you must gybe at the layline.