A course a boat would sail to 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.

What does the layline have to do with proper course?Edit

This is one of the most commonly argued matters especially when it comes to rule 17.1 because the auto-umpire in VSK does appear to use the computed layline in it's algorithm for determining whether or not a boat is sailing her proper course. The layline to a mark is not necessarily the proper course because a skipper may need to factor such variables as wind shifts, stream, tide and obstructions into the decision making process for determining the proper course.

This is one of the reasons why you may often see a race announced as "NPC except 17.1"

If my best course is the course I would sail to finish as soon as possible then isn't that the same as my proper course?
Most of the time it is the same. In fact the concept of "proper course" only comes into play when one of these three rules is cited as reason for a protest.
  1. Rule 17
  2. Rule 18
  3. Rule 23

Rules 17, 18.4 and 23 restrict you from sailing beyond your proper course even if doing so would be a better course for you to sail. Rule 18.5b actually protects your right to sail your proper course as you round a mark provided that you are taking mark-room to which you are entitled.

File:Proper course stable elements.gif
File:Proper course wind shift.gif
File:Proper course stream.gif
File:Proper course obstruction land.gif
animated illustrations wanted
File:Proper course fleet.gif