SailRacer

ToT PHRF pre race calculation

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Does anybody have a spreadsheet that I can use to figure out our position during (or shortly after) a race?

coming up on a 6 race series that puts us against a boats with a rating  as much as 130 sec diff in PHRF. We are the slow boat and would like to keep track on how we are doing 15, 30, 45 and 60 min into the race.

( nothing like a Tänzer 22 vs a 10R or H33 but, I like the challenge and may be able to capitalize on any mistakes).

Any good ideas or tips welcome. Thanks 

Sail Safe! : )

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I have a spreadsheet in Google Sheets.  It might convert to MS Excel.  PM me.

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Can’t really work without a time difference between you and the other boats.

 

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PHRF is a Time on Distance formula.  Per my favorite mathematician:  Converting to a ToD number ToT is essentially multiplying one approximation by another approximation.  A guaranteed way to increase inaccuracy.   ToT also increases its inaccuracy the larger the rating spread.  It's not bad in narrow bands, but at each end of the rating band, the conversion factor - which is based on an assumed "average" boat performance - gets increasingly distorted.   

Plus, as you are finding out, it is a pain to use on the race course.  

Do your mid-race calculations using ToD and you'll get close enough for tactical/strategic purposes.

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Thanks that is what I have used in the past as an approximation.

hate that word.

sail Safe 

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2 hours ago, Left Shift said:

PHRF is a Time on Distance formula.  Per my favorite mathematician:  Converting to a ToD number ToT is essentially multiplying one approximation by another approximation.  A guaranteed way to increase inaccuracy.   ToT also increases its inaccuracy the larger the rating spread.  It's not bad in narrow bands, but at each end of the rating band, the conversion factor - which is based on an assumed "average" boat performance - gets increasingly distorted.   

Plus, as you are finding out, it is a pain to use on the race course.  

Do your mid-race calculations using ToD and you'll get close enough for tactical/strategic purposes.

I use a slight modification of this.  I keep track of the time raced, and then multiply by my average boatspeed (its a 6 kt shitbox) to get "rated distance travelled so far".  Then use the ToD corrections.  This works because if you are becalmed for an hour, in TOT slower rated boats are catching up to faster rated boats even though no-one is moving.  Just using regular TOD using distance covered over the ground does not account for that factor.

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7 hours ago, Left Shift said:

PHRF is a Time on Distance formula.  Per my favorite mathematician:  Converting to a ToD number ToT is essentially multiplying one approximation by another approximation.  A guaranteed way to increase inaccuracy.   ToT also increases its inaccuracy the larger the rating spread.  It's not bad in narrow bands, but at each end of the rating band, the conversion factor - which is based on an assumed "average" boat performance - gets increasingly distorted.   

Plus, as you are finding out, it is a pain to use on the race course.  

Do your mid-race calculations using ToD and you'll get close enough for tactical/strategic purposes.

I've noticed a several races, mostly light winds, where ToT formula finished the entire fleet in exact reverse order of PHRF rating.  

Now, we know that PHRF works best for average conditions. But on opposite ends of the spectrum, not so much. 

But no doubt if you are the showboat and winds are light - ToT in your friend. 

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6 hours ago, dash34 said:

I use a slight modification of this.  I keep track of the time raced, and then multiply by my average boatspeed (its a 6 kt shitbox) to get "rated distance travelled so far".  Then use the ToD corrections.  This works because if you are becalmed for an hour, in TOT slower rated boats are catching up to faster rated boats even though no-one is moving.  Just using regular TOD using distance covered over the ground does not account for that factor.

My view is that if you are becalmed for an hour (in a day race) , you really aren’t sailboat racing anymore.  There might be a “winner”, and it might even be me, but whoever it is didn’t win an actual sailboat race.

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10 hours ago, dash34 said:

I use a slight modification of this.  I keep track of the time raced, and then multiply by my average boatspeed (its a 6 kt shitbox) to get "rated distance travelled so far".  Then use the ToD corrections.  This works because if you are becalmed for an hour, in TOT slower rated boats are catching up to faster rated boats even though no-one is moving.  Just using regular TOD using distance covered over the ground does not account for that factor.

Yep, another version is to assume the zero boat goes 6 knots, so multiply the tod rating difference by 6 and divide by 60 for # of minutes per hour racing allowed.  If it’s the same fleet all the time, the time differences will be constant.  Tod is not much less complicated imo, unless you’ve got a pretty reasonable idea of the distances.

 

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Below is an example of what I use for racing in IRC,  I have similar one for PHRF club racing, it's just not with me now. Google PHRF Primer, there is a chart out there with the seconds/mile for each rating band, I have that also, just not here. Or send me the rating and I will generate it for you, it's not exact as "Q"factors vary, but it will help.

 

Yacht

TCC 1 Hr 30 Min 20 Min 10 Min
Margaritaville 0.996 2:28 1:14 0:49 0:24
Black Magic 1.002 2:05 1:02 0:41 0:20
Red Jacket 1.003 2:02 1:01 0:40 0:20
Perfect 10 & Blast 1.011 1:32 0:46 0:30 0:15
Crime Scene 1.024 0:45 0:22 0:15 0:07
Bene 36.7 1.03 0:24 0:12 0:08 0:04
Great Escape 1.036 0:03 0:01 0:01 0:00
Five Fifteen 1.037 0:00 0:00 0:00 0:00
Lively (owe me) 1.039 0:06 0:03 0:02 0:01
Shockwave (owe me) 1.041 0:13 0:06 0:04 0:02
IMXtreme (owe me) 1.045 0:27 0:13 0:09 0:04

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Not all PHRF ToT is the same.

Check to see which ToT formula that your PHRF organization uses.

Some organizations modify the high and low numbers or add a ‘Q’ factor (as we do in PHRF-LO) based on local conditions.

As a rough guess on the race course, you can figure about the points difference between the boats every 12 minutes.

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Here's the spreadsheet I use.  As Kirby Nitwit mentions above, check to see if your OA/YRA uses a specific "B-Factor".  That can be entered in the highlighted cell near the top of my spreadsheet.  For a quick reference, I have added conditional formatting based on the rating so that if a boat owes you time, a ll the info on that line will be in red.

Time Differential-SA.xlsx

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