In the U.S. we mostly use time on distance, i.e. so many seconds per mile for the PHRF ratings. In Europe and other places time on time is used more, i.e. so many seconds per hour. To me, time on time makes more sense. To have a 1/4 mile lead in race with 15kts of wind with everyone at hull speed vs a 1/4 mile lead in a drifter is very different. My understanding is that in time on time races the corrected times bring the boats closer together which suggests a more competitive race. I would be interested in others' thoughts on the subject.
PHRF - Time on time vs time on distance
- Thread starter markwbird
- Start date
We use time on time. I think it's just easier for the scorer. The arithmetic is just TimeCorrectionFactor X elapsed time = corrected time. For those who don't know there are several coefficients which can be used to get the TCF.
Here's a reasonable explanation from USSA Website PHRF :
A
TCF = ——————
B + PHRF
The denominator, B + PHRF, is the number of seconds it takes to sail a nautical mile in the expected conditions. Another way to look at it is that the denominator divided into 3600 is the average rhumb line boat speed in knots. Here are some commonly used B factors:
B Factor
When Used
480
Heavy Air or all off the wind
550
Average conditions
600 Light air or all windward work
There are no hard and fast rules for selecting the B coefficient. Basically, the lower you select it, the more favorable it will be to the slower boats.
The numerator, A, is merely a coefficient that makes a “nice” looking TCF. Select it so that the TCF for the middle of the fleet is about 1.000. The A coefficient has absolutely no effect on the corrected finish order. Changing it will only affect the various margins. Thus if your middle handicap is about 100 and your conditions are average, then the TCF formula would look like the following:
650
TCF = ——————
550 + PHRF
To get the corrected time, simply multiply the elapsed time by the TCF.
TOT scoring is not a cure-all for all the inequities of handicapping. TOT scoring will not turn a fleet upside down. It usually does not affect the top boats. It usually moves the boats in the middle around a little. If the handicap spread in a class is large, it will tend to tighten things up a bit.
- See more at: http://www.ussailing.org/racing/offshore-big-boats/phrf/time-on-time-scoring/#sthash.5DMN7mON.dpuf
Simple right?
Here's a reasonable explanation from USSA Website PHRF :
A
TCF = ——————
B + PHRF
The denominator, B + PHRF, is the number of seconds it takes to sail a nautical mile in the expected conditions. Another way to look at it is that the denominator divided into 3600 is the average rhumb line boat speed in knots. Here are some commonly used B factors:
B Factor
When Used
480
Heavy Air or all off the wind
550
Average conditions
600 Light air or all windward work
There are no hard and fast rules for selecting the B coefficient. Basically, the lower you select it, the more favorable it will be to the slower boats.
The numerator, A, is merely a coefficient that makes a “nice” looking TCF. Select it so that the TCF for the middle of the fleet is about 1.000. The A coefficient has absolutely no effect on the corrected finish order. Changing it will only affect the various margins. Thus if your middle handicap is about 100 and your conditions are average, then the TCF formula would look like the following:
650
TCF = ——————
550 + PHRF
To get the corrected time, simply multiply the elapsed time by the TCF.
TOT scoring is not a cure-all for all the inequities of handicapping. TOT scoring will not turn a fleet upside down. It usually does not affect the top boats. It usually moves the boats in the middle around a little. If the handicap spread in a class is large, it will tend to tighten things up a bit.
- See more at: http://www.ussailing.org/racing/offshore-big-boats/phrf/time-on-time-scoring/#sthash.5DMN7mON.dpuf
Simple right?
Out yacht club uses time on distance. I've thought about proposing ToT, but I don't know that the membership would go for it. With ToD it's relatively easy for a boat to figure out if they beat a competitor before the results are finalized. Just estimate the course distance and multiply by the difference in handicaps to get the correction. I suspect many people wouldn't like the relative difficulty of figuring out how they placed in ToT.
I'm not a advocate of TOT over TOD but you can still look at a scratch sheet, figure the seconds per mile differential, the distance and get to a reasonable estimate of your position. Both ways are imprecise and that's why we go to awards ceremonies. I don't know what a race would be without someone, usually the skipper, calling for the scratch sheet on the last leg, and a back and forth about how the boat did. One design is so ... boring.
Ummm.... no (at least not for me!) How do you know what values the Committee will be using for A and B so you can know where you stand in the race? It's easy to calculate your corrected position in a race with ToD (you just have to know the race distance and the other boats' rating), but basically impossible with ToT.
druid
Again, I'm not here to defend TOT. In practice our RC's use the middle number, 550. As far as estimating your position against other boats I don't think TOT is that different from TOD. IF you figure you beat someone on time via TOD, you probably beat them via TOT. We regularly use the scratch sheet PHRF numbers to estimate our position based on TOD, and end up right in relative positions most of the time. I'm saying there isn't an operational difference of significance. There are some differences on longer races or in races in which conditions change, and in fleets where the spread is too large, but it's nearly impossible to have a completely fair rating system for fleets of wide diversity of contestants in all wind conditions on all courses.
TOD is definitely simpler and, I believe, there in lies the problem. I feel that the reality of different boats in different situations, windspeed, chop, upwind, downwind, etc, is complex and a handicapping system that really addresses these complexities is in order. In this day and age of computers and mathematical whiz kids solving crimes on TV someone should come up with a more sophisticated system. Who is that guy from Moneyball? Let's get him.
I'll be the devil's advocate here. If TOT doesn't really impact the finish order, why bother? If it does, I guarantee someone will be whining about the arbitrary choice of "B-factor". That being said, I have never had the opportunity to participate in a TOT race, so I could be completely off base.
It does impact the finish order for the middle range boats. More importantly, it brings the boats closer together to make a more competitive race so that the finish order has a better chance of changing.
[QUOTE="Sandy Stone, post: 1321971, member: 73633" If TOT doesn't really impact the finish order, why bother? If it does, I guarantee someone will be whining about the arbitrary choice of "B-factor". .[/QUOTE]
A very good question. As I said I think it's easier for the scorer. Not necessarily for the contestants. We've had virtually no complaints from the fleet regarding the choice of B-factor. I might ascribe that to the fact that few of the fleet have looked that far into the formula and are hence ignorant of the fact that it can change with conditions.
A very good question. As I said I think it's easier for the scorer. Not necessarily for the contestants. We've had virtually no complaints from the fleet regarding the choice of B-factor. I might ascribe that to the fact that few of the fleet have looked that far into the formula and are hence ignorant of the fact that it can change with conditions.
ToT has a couple of very distinct advantages.
First, it is much easier and more accurate to measure time rather than distance. If the course is off by a few yards, the calculations will be incorrect. With ToT course length does not matter, 1 mile, 1.01 miles, 1.1 miles its all the same, the elapsed time is what matters.
Second, weather on a race course is seldom consistent. In a dying breeze, big fast boats have a distinct advantage as they spend more time in the good breeze, while smaller slower boats get beat up by the lack of wind. With ToD the boats have sailed the same course but the smaller boats will have disproportionately longer elapsed times. With ToT it matters less because the ET is corrected by the ToT rating, not the distance.
Converting a ToD rating to a ToT rating involves some mathematical magic, but it is relatively easy to compare finishes using ToD results and ToT results and adjust the formula. It would be even better to completely abandon the ToD ratings and only use ToT ratings.
Creating accurate simple ToT ratings is pretty straight forward. Local clubs can do their own with a spreadsheet. The tricky part (and the math that I don't fully comprehend) is adjusting for different fleets. ToT ratings are all based on a "base boat" where the ToT multiplier is 1.
To calculate a local ToT rating that is only good for one fleet, simply find the median time for each race and then calculate the ToT number for each boat in the race. Collect data from at least 5 races and take the median rating for each boat.
Local ToT Rating = Boat's Elapsed Time/Median Elapsed Time Fleet
Some thoughts on how to do this and why can be found here: http://www.sailingscuttlebutt.com/2016/04/27/focus-on-fairness-in-local-competition/
First, it is much easier and more accurate to measure time rather than distance. If the course is off by a few yards, the calculations will be incorrect. With ToT course length does not matter, 1 mile, 1.01 miles, 1.1 miles its all the same, the elapsed time is what matters.
Second, weather on a race course is seldom consistent. In a dying breeze, big fast boats have a distinct advantage as they spend more time in the good breeze, while smaller slower boats get beat up by the lack of wind. With ToD the boats have sailed the same course but the smaller boats will have disproportionately longer elapsed times. With ToT it matters less because the ET is corrected by the ToT rating, not the distance.
Converting a ToD rating to a ToT rating involves some mathematical magic, but it is relatively easy to compare finishes using ToD results and ToT results and adjust the formula. It would be even better to completely abandon the ToD ratings and only use ToT ratings.
Creating accurate simple ToT ratings is pretty straight forward. Local clubs can do their own with a spreadsheet. The tricky part (and the math that I don't fully comprehend) is adjusting for different fleets. ToT ratings are all based on a "base boat" where the ToT multiplier is 1.
To calculate a local ToT rating that is only good for one fleet, simply find the median time for each race and then calculate the ToT number for each boat in the race. Collect data from at least 5 races and take the median rating for each boat.
Local ToT Rating = Boat's Elapsed Time/Median Elapsed Time Fleet
Some thoughts on how to do this and why can be found here: http://www.sailingscuttlebutt.com/2016/04/27/focus-on-fairness-in-local-competition/