There have been few questions about Rule 18 at the windward mark during our Monday races, and a bit of confusion when it turns off and on. I have been asked to explain Rule 18 at the windward mark. The rules writers have made it so that Rule 18 only applies between boats on the same tack and that when on opposite tacks the normal right of way rules of Parts A and B apply. Also, Rule 18 makes it quite difficult on those that approach the mark on the port lay line and tack at the mark. This appears to be popular in our fleet when we have a westerly and the left side of the course is favored, but it needs to be done with caution because you have very few rights and many responsibilities when you approach the windward mark on port and tack in the Zone.

The figure on the left shows Yellow on the starboard lay line and Blue 1.5 lengths below the port lay line. Let’s walk through the rules that apply during this encounter. At positions 1 and 2 Blue is port and must keep clear of Yellow. If you look at Rule 18.1 it gives 4 cases when rule 18 does not apply. The first one of these is Rule 18.1(a) which tells us that rule 18 does not apply when boats are on opposite tacks on a beat to windward. Therefore the normal right of way rules apply and Blue must keep clear.

As soon as Blue passes head to wind while she is tacking, she must keep clear of Yellow until she is on a close hauled course by Rule 13 just like anywhere else on the course. Rule 18 begins to apply as soon as Blue passes head to wind and is on the same tack with Yellow, but what section of Rule 18 applies? Because Blue tacks inside the zone Rule 18.3 applies and 18.2 does not, so Blue is not entitled to mark-room. But, she is leeward boat so she has right of way and Yellow must keep clear as windward boat. But, rule 18.3(a) limits Blue’s luffing rights because she cannot cause Yellow to sail above close hauled. In the diagram Blue breaks Rule 18.3 and fouls Yellow because Yellow was forced to sail above close hauled.

The middle diagram illustrates Rule 18.3(b). If Blue tacks inside the zone and Yellow gets a late overlap inside at the mark, then Blue must give Yellow mark-room. Yellow is entitled to luff to round the mark and Blue must keep clear. One thing Yellow must be careful of is to turn down and not sail above her proper course at the mark. This is because she has established her overlap from clear astern and Rule 17 says she must not sail above her proper course while they remain overlapped on the same tack.

The diagram on the right shows an interesting quirk in the rules. If you read the definition of mark-room it does not include room to tack unless the boat entitled to mark-room is overlapped to windward of the boat required to give it. In this case Yellow enters the zone clear ahead and to leeward of Blue. Therefore, she is entitled to mark-room but not room to tack at the mark. She must not break Rule 13 as she tacks or Rule 15 when she acquires right of way on starboard tack. So you need to be careful when you are on the port tack lay line with a boat clear astern of you on your hip. You are entitled to mark-room but it doesn’t include room to tack. Yellow can luff head to wind but better not pass head to wind or she will probably foul Blue.