Feature request: add VMC to the dashboard

Can you add VMC to the dashboard with SOG, VMG, Heel, and drift?

Topic

[Sergey Lubarsky]

Jeff,

 

We use a combination of VMG and VMC in the dashboard. Such as upwind it will show VMC and in all other points of sail VMG.

[Jeff Taylor]

I don’t see it.  I’m replaying a race now and we are sailing upwind and it is showing me VMG.  At this point in the race, I am sailing on the lay line directly toward the mark, my displayed SOG is 5.0 kts and my VMG is 4.3 kts.  The 4.3 kt vector is pointing not at the mark, but directly up wind.  I’d expect VMC = SOG at this time as my course is directly at the mark.

[Christopher W]

I have the same issue and agree with Jeff’s observations.  See attached pic.

 

 

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[Jeff Taylor]

Yes, that ^^^^^

 

VMG is good to know, glad to have that data, but adding VMC would be nice too.

[raceQs]

Let us explain how raceQs works:

–  on upwind legs the tool shows VMC – the speed toward the wind direction.

– on downwind and reaching legs the tool shows VMG – the speed toward the mark direction.

 

The upwind leg is defined as any destination point you can’t reach w/o at least one tack. This logic work works fine for most of the cases except two rear exception.

– Upwind  leg when the boat on or above lay line – you are not supposed to hit the corners.

– Off wind leg  if you went a wrong way and need to tack to reach the mark.

Looks like we need to add a switch when the user can chose VMG vs. VMC .  Please provide your comments.

 

[Christopher W]

First off I suppose is a mutually agreed upon definition of VMG/VMC.  The definitieons I use which I find tend to be most prevalent on the internet are:

VMC is the Velocity Made good  on Course. i.e. Speed in the direction of the mark.

VMG is the Velocity Made Good i.e. Speed in the upwind of downwind direction.

Thus, it sounds as though RaceQ’s is using these definitions backwards from what I’d expect, base do the definition provided above by the developer.

Regardless of the nomenclature, I definitely want to know my speed made good towards the MARK whether it is upwind or downwind.  This is especially true since RaceQ’s uses analytic predictions of where the wind is coming from, whereas the mark position is typically known with certainty.

[Jeff Taylor]

I agree with Chris’s definitions of VMC(ourse) and VMG(ood).  In my book, the replayer is plotting VMG all the time.  That’s what it says it is doing, and that’s what it is doing by the commonly accepted definitions of VMC and VMG.

What we are asking for is velocity toward the mark.  I don’t know what to call that other than VMC.  Whatever definitions you use, they should be consistent no matter which direction we are sailing.

[Jeff Taylor]

Ok, on playing with it some more, I do see times when it is plotting something other than VMG.

 

On reaching legs, I see it plotting VMC where “C” is the rumbline course, not the course from my position to the mark.  I guess that makes sense, but I’d still like to know the VMC where C is the course from my position to the mark.

[Jeremy]

I still see it displaying only VMG (to the wind) on any leg.

 

Not all races are perfectly upwind/downwind. Lots of little local traditional regattas have set (random leg) courses that are run every year regardless of wind direction. It is preferable to actually have both measurements (VMC & VMG) available on the legs of these courses, particularly in light wind. In this case, velocity to the wind (VMG) tells you how well you’re pointing relative to the wind, and VMC (course) tells you whether or not you missed a wind-shift. IMHO, both calculations (or something meaningful and similar) should be available in all points of sail. Obviously this may create confusion w.r.t. any downwind run since VMG (wind) is negative. Personally I don’t have an issue with that, and while I haven’t thought about it I would guess there would be an easy way to calculate out a particular boats polar performance (and show performance relative to that) with enough successive tracks in the database.

 

But definitely, Velocity to the MARK and relative to the WIND are both important, imho important on all points of sail.

[Joe Mattea]

The VMG feature… as it occurs now… is, obviously, confusing to a number of us. Like Chris & Jeff, I’ve always thought of VMC as being in relation to the next mark and VMG as being in relation to the wind direction. THAT NEEDS TO BE SPELLED OUT CLEARLY ON THE REPLAY SCREENS. I’d like to have both but, if I could only have one it would be VMC (as I defined above).

 

[Author]

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