Not to "nerd out," but "speed" has time in the denominator. That is it is distance over time. So whatever  portion of the course you are sailing--say, getting around the leeward mark, "quickly as possible" would mean sailing that course in the shortest time.
I don't think there is any conflict.

There are two meanings of "course" in the rules.  There is the "course" which is the route of the race, as defined in "Finish". There is also the "course" which is the direction the boat is aiming, as in Rule 16.1. I don't think the R16.1 meaning is appropriate here, so my money is on the route to sail the race. I.e. the "quickly as possible" can only refer to Finish the race as a whole in the shortest time.

I agree with Anthony, but use a much less formal argument. In ordinary English usage, if someone were to ask me to do a certain task quickly, they would be asking me to do it In a short time. This definition refers to a task, sailing the course, and so I conclude a proper course is the course that completes that task in the shortest time.

The bigger problem word in the definition of property course is "choose", because a boat may choose wrongly. They might want to sail high to get to a shift or current that they think it's coming, but are wrong about it. 

I think in most club racing, proper course rules really only apply for the most blatant of luffs because any boat can hand on heart day they think it was quicker to choose to sail higher

There is also the word “course”.   It is not just a matter of sailing quickly, but sailing the course in the absence of the other boat involved.  Often there are races at the end of a regatta where one  boat needs to simply place ahead of another boat to win the regatta and there is a 2 boat match race, with each boat finishing far behind the leaders of that particular race.  Is either boat sailing the course ? quickly ?  Each is only trying to stay ahead of its rival.   If a protest involved only the other boat, it might be argued that in the 2 boat match race each is choosing a course to beat his rival and win the regatta, but is that sailing the course?

I'm not sure the match racing another boat applies as the definition is in the absence of other boats. So even if you only need to beat 1 boat. If that boat was not there, then you'd not know where to sail to beat it.... Unless hand on heart you say you really thought there was a more favourable current far off to the right of the course and it was only a coincidence that your main rival was there and that you took them all the way to the back of the fleet when that current didn't materialise as you thought it would. /S

Greg, "choose" got added in 2021.  I liked the addition because it underlined the concept that there is not just one solution available to a boat that could qualify for a "proper course". 

Before that def: PC just said "A course a boat would sail ..." and I had the opinion that a lot hung on the "A" in the beginning of the sentence to covey the idea of 'one of possibly many' (a reader would have had to note that it said "A" instead of "The"). 

I think the exchange of "as soon as" for "as quickly as" is just better grammar with the addition of "sail the course", because STC can be thought of as a continuing action in the moment as well as something a boat does to completion (where "finish"'is a completion-only action).  

In that way, "quickly" captures (and I think is a better word-pairing with) the on going nature of the act of "sail the course" more than "soon" (as in ... 'to work quickly to finish soon')

PS: I don't think that "choose" removes the reasonableness-test of the actions of a boat. They can't just cross their heart. They still have to convince a PC (if it came to that) that it was a reasonable choice to STC and finish as quickly as possible. 

Others have alluded to it, but "sail the course" is a defined term, essentially meaning to go from start to finish around the marks. It's not really up for debate which version of "course" is intended here. I think it's pretty clear in context that sailing the course quickly is the time it takes, not the average speed achieved during the race. A quick google of the phrase "as quickly as possible" confirms this. I also don't think there's any doubt that the rule is intended to force boats to sail to the finish quickly, as opposed to ask boats to defeat a nearby competitor. It specifically places these two goals at odds with each other such that you cannot play spoiler and choose which competitor to defeat when you're in a "barely ROW" situation. Doesn't stop you from doing that if you are ahead to begin with though.

Does that not add some ambiguity into it in that if we all knew the fastest route we would all do better than we do? What if two boats disagree on the fastest route ?

Adrian: that is fairly well addressed in case 14. 
Two boats can disagree on proper course. The ROW boat is given a fair bit of deference in choosing their own proper course. Note that the case states that the fastest course cannot necessarily known and the fact that one boat gets to the mark faster than another does not invalidate the other's choice. I'm not explaining that fully. The case does a better job. 

14

"When, owing to a difference of opinion on the proper course to be sailed, two boats on the same tack converge, W is bound by rule 11 to keep clear and by rule 14 to avoid contact.
This case illustrates the fact that two boats on the same leg sailing very near to one another can have different proper courses. Which of two different courses is the faster one to the next mark can not be determined in advance and is not necessarily proven by one boat or the other reaching the next mark ahead."

Angelo,

I agree that "choose" does capture the fact that there can be more than one solution (real or perceived) to the "quickest" way around a course.   It also means that RRS17 only really applies to blatant "unreasonable" luffs once an overlap is established, which ultimately means that it is hardly ever applicable to club racing.... which is good (less rules to think about).   For anything short of such a blatant luff, I tell my fleet that it is pointless yelling "sail your proper course" to a boat slowly pushing you up, because it is never 17.

I agree with Greg. In my 60 plus years of racing sailboats, I have literally never been in a boat that established an overlap to leeward from astern and then luffed the other boat, in a fleet race. Luffing is reserved by almost all sailors for a defense against being overtaken to windward, not as a weapon when overtaking to leeward.

I also implore everyone to not try to find obscure or complex interpretations of the words used in the rules.  While it's true that the rules are meant to be read literally, they are also meant to be used in context, so the words in those rules should be interpreted in the context in which each rule applies. In other words, within the range of possible literal interpretations, we should take the one that suits best. I personally think that the expression "A course a boat would choose in order to sail the course as quickly as possible" is clear and unambiguous in context. "Course" means the direction or path a boat travels in,  "A course ... choose" implies that there may be more than one, "would" means the determination is hypothetical, and (to answer the original question) "quickly" means in the least time possible. 

The one issue here barely touched on in this thread is that the rules involving proper course, like all the other rules, are interpreted on a moment-to-moment basis. So the course a boat would take to achieve a certain purpose means the course she would take, given the position she is in at the moment. Take rule 17, for example. The proper course for a reaching leeward overlapped boat is frequently to turn to the rhumbline to the next mark. The fact that, at the moment the rule begins to apply, she is sailing 45 degrees above that rhumbline is irrelevant. The issue is, from that point, what would she choose to do, to sail the course as quickly as she can?

I want to second Rob's plea: don't go looking for obscure definitions. For terms not defined in the rules, we go to common definitions, such as in the dictionary or common use. Sometimes a word can have different common meanings. If one of the common meanings makes the rule seem stupid or impossible to apply, don't use that definition. Use the common definition that makes the rule make sense. 

Greg re: "For anything short of such a blatant luff, I tell my fleet that it is pointless yelling "sail your proper course" to a boat slowly pushing you up, because it is never 17."

Not only pointless ... but risky (since 17 doesn't covey room to the windward boat) and based on a false notion of PC and understanding of rule 17. 

The words people use can be a window into their understanding. So many racers hold the concept in their heads as exemplified by your fleet members' command to another boat, "Sail your proper course!". I think the introduction of "choose" makes some progress in correcting it. 

First  "sail your proper course!" illustrates the notion that there is single well-defined course (there often isn't).  Second it implies there is some rule which requires a boat to sail this course (there isn't). 

I spend a lot of time trying to pry-free those 2 ideas.  

Angelo-- point taken that the boat needn't sail her proper course (a lower course is OK).

But given that rule 17 itself says "her proper course", I wouldn't interpret a sailor saying "your proper course" as implying there's only one.

Is there a concise wording you'd suggest?

David re: "Is there a concise wording you'd suggest?"

Yea .. "Protest!" ;-)  .. that tends to get someone's attention.