RULE 18.4
Gybing

Let’s look at what the rule says:

18.4 Gybing

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.

Rule 18.4 Correct Gybing
Example 1
Yellow acts in accordance with 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.

Rule 18.4 does not apply at a gate
Example 2
Yellow acts in accordance with Rule 18.4
Scenario 1

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.

Rule 18.4 Not on proper course

Is yellow breaking Rule 18.4?

Take a few seconds to look at the scenario. Does Rule 18 apply and if so does 18.4 kick in?

YES, yellow breaches Rule 18.4

Yellow, as the inside overlapped right-of-way boat, require to sail her proper course. This means that at position 4 she needs to gybe and round the mark.
Scenario 2

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.

Rule 18.4 gate 4 boats

Which boats must keep clear?

Take a few seconds to look at the scenario. Rules apply between 2 boat. What are the options of each boat in relation to Rule 18.4 or any other rules?

Rule 18.4 does not apply

Yellow must keep clear of all boats because she is the windward boat on a port tack. Blue can gybe around the west mark or round the east mark where it needs to keep clear of red and green (Rule 10 - opposite tacks). Red needs to keep clear of green as she is the windward boat. Yellow can gybe and round the east mark or round the west mark as both options could be considered her proper course. In any case, Rule 18.4 does not apply because we are looking at a gate mark.

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.

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