Rule 17

On the Same Tack; Proper Course

Rule 17 - ON THE SAME TACK; PROPER COURSE

If a boat clear astern becomes overlapped within two of her hull lengths to leeward of a boat on the same tack, she shall not sail above her proper course while they remain on the same tack and overlapped within that distance, unless in doing so she promptly sails astern of the other boat. This rule does not apply if the overlap begins while the windward boat is required by rule 13 to keep clear.

Note

  • Different boats may have different proper courses.
  • A boat's proper course may be to change course (for example, to catch a puff).
  • This rule limits the actions of the right-of-way boat to her proper course. The proper course of the keep clear boat is irrelevant.

Relevant Definitions

Keep Clear

A boat keeps clear of a right-of-way boat

(a) if the right-of-way boat can sail her course with no need to take avoiding action and,

(b) when the boats are overlapped, if the right-of-way boat can also change course in both directions without immediately making contact.

Clear Astern and Clear Ahead; Overlap

One boat is clear astern of another when her hull and equipment in normal position are behind a line abeam from the aftermost point of the other boat’s hull and equipment in normal position. The other boat is clear ahead. They overlap when neither is clear astern.

However, they also overlap when a boat between them overlaps both.

These terms always apply to boats on the same tack.

They apply to boats on opposite tacks only when rule 18 applies between them or when both boats are sailing more than ninety degrees from the true wind.

Tack, Starboard or Port

A boat is on the tack, starboard or port, corresponding to her windward side.

Leeward and Windward

A boat’s leeward side is the side that is or, when she is head to wind, was away from the wind.

However, when sailing by the lee or directly downwind, her leeward side is the side on which her mainsail lies. The other side is her windward side.

When two boats on the same tack overlap, the one on the leeward side of the other is the leeward boat. The other is the windward boat.

Proper Course

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.

Yellow takes Blue up

Scenario 1:

  • Yellow establishes a Leeward overlap, from clear astern, within two hull-lengths to leeward. Rule 11 and Rule 17 are therefore in effect.
  • Yellow then sails above her proper course, taking Blue up.
  • Yellow has broken Rule 17. Had Blue not been there, Yellow would not have changed course.

Scenario 2:

  • Yellow establishes a Leeward overlap, from clear astern, within two hull-lengths to leeward. Rule 11 and Rule 17 are therefore in effect.
  • Yellow's proper course is higher than Blue's proper course.
  • Yellow takes Blue up.
  • Yellow has not broken Rule 17, as she has not sailed above her proper course. Blue's proper course is irrelevant.

Scenario 3:

  • Yellow establishes a Leeward overlap, from clear astern, within two hull-lengths to leeward. Rule 11 and Rule 17 are therefore in effect.
  • Yellow sees new breeze, and changes course to get to it.
  • Yellow has not broken Rule 17, as she would have changed course to get to the new breeze even if Blue wasn't there.