Bob, we had a similar topic recently here …

“Is the offset a separate mark for RRS 18 ?”

Thanks for the referral, Angelo.

In sailing, an offset mark is used to set a fair course when the windward mark is close to something that could make tracking difficult. It is usually put to one side of the windward mark to make a clear border or offset zone. To finish the course properly, sailors must go around both the windward mark and the offset mark.

The offset mark's job is to make sure that sailors can safely and fairly get around the challenge or barrier. By having a separate mark, it's easy to give clear directions and keeps competitors from getting confused. The offset mark is usually put in a spot that takes the direction of the slope wind and other things into account so that it can be used as a good adjustment point.