R17

R17 ILLUSTRATED

17 ON THE SAME TACK . PROPER COURSE

17.1 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 overlapped within that distance, unless in doing so she promptly sails astern of the other boat. This rules does not apply if the overlap beings while the windward boat is required by rule 13 to keep clear.

définitions :
- 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.

explanations :
A boat catching up another boat on the same tack, and not further than 2 hull lengths from her laterally and that chooses to overlap that boat to leeward of her has no luffing right.
Note than in theory when being luffed by a boat without luffing right, the proper behavior is to respond to the luff and then protest the move.
Rule 17.1 does not take precedence over rule 11. A windward boat must stay clear of a leeward boat. Rule 17.1 only limits the luffing rights of the leeward boat.

In summary :

Catching from behind = no luffing right
Being caught from behind = luffing right
Establishing overlap while maneuvering (tack or gybe) = luffing right

Here are a few examples in which Blue is constrained by rule 17.1.

Note that in the downwind case (on the right), Blue will have to gybe at the layline in order not to sail above her proper course (in the absence of Yellow, Blue would gybe on the layline to finish the course as quickly as possible).

And here are a few cases where Blue is not constrained by rule 17.1

If the windward boat is constrained by 13 when the overlap is established, the leeward boat is not constrained by 17.1 and has acquired luffing rights –up to head to wind.
Here is an example in which Blue is constrained by 13 when the overlap is established. 17.1 is therefore not applied in this situation.

For 17.1 not to be applied when a boat is changing tacks, it is necessary that the overlap has been established during the tack or gybe –and not broken at any point in time during the maneuver.

17.2 Except on a beat to windward, while a boat is less than two of her hull lengths from a leeward boat or a boat clear astern steering a course to leeward of her, she shall not sail below her proper course unless she gybes.

explanations :
17.2 is not applied on upwind legs (beats to windward). It is only applied on reaching and running legs.
17.2 prevents a windward boat, or a boat slightly ahead and “windward” of a boat slightly behind her, from bearing away to “close in” on that other boat.

tactical aspects of the rule :
Note that 17.2 is not applied at all in match racing. The lack of 17.2 in match racing allows a boat clear ahead to close in on the trajectory of the boat following and try and stay in front (being protected by e.g. rule 12).

implementation in vsk3 :
17.1 is by and large well managed by VSK3 (including in the layline cases). The definition of proper course being often quite lenient (VSK3 allows for very tight angles to be considered proper course, especially downwind)
17.2 is however overly sensitive in the game. It is worth noting that VSK3 considers proper course to be the heading of the *leeward* boat. i.e., rather than her own angle, the windward boat must make sure she stays at or above the heading of the leeward boat, regardless of whether this is above or below what she would normally consider her proper course. For instance, should the leeward boat luff for any reason, the windward boat should luff asap herself in order to avoid a –unjustified- pen under 17.2.

bye rafat - translation bye amic.