PHRF Scoring

Time on Distance & Time on Time

TOD – TOT

At the awards dinner for the Falkner Island race, I had occasion to overhear several conversations regarding the benefits (plus and minus) of the “Time on Time” vs. “Time on Distance” methods of scoring. It became clear that there are some misconceptions regarding these two systems. As author and designer of the spreadsheet scoring system used by the “Around the Buoys” racers, I would like to take a few minutes to briefly outline the mechanics of the two systems.

“Time on Distance”:

Probably the most straight forward method for determining how your boat finishes in a given race. The information required boils down to: knowing your handicap, and your competitors’ handicaps, and the length of the race course. In its simplest terms you calculate the difference in handicaps between yourself and your competitors then multiply that number by the course length. The result will be the difference in “seconds” in order for one boat to tie the other.

In order to calculate the final standings of a regatta using T.O.D., a benchmark time is needed. That benchmark is provided by the “Scratch Boat.” There is nothing unique about the Scratch Boat, other than it is the first boat to finish. That is why there are no changes to the “Scratch Boats” time when the final results are posted. All boats that finish after the scratch boat will then have their finish times corrected by the difference in their PHRF rating vs. the Scratch Boats rating. If your boat has a higher rating then the scratch boats, the difference in the two ratings, multiplied by the course length will produce a time in seconds that will be subtracted from your actual finish time. That time is called: “Corrected Time.”  On the other hand, if your rating is less than the scratch boats, the difference of the two ratings multiplied by the course length will produce a time in seconds that will be added to your actual finish time.

Time on Distance is a simple system but favors longer waterline boats when the conditions are such that hull speed can’t be maintained! Example; Course “A” 5.4 nautical miles start to Finish. Two boats racing with PHRF’s of 177 and 220, the difference in PHRF’s is 43. 43 seconds multiplied by 5.4 yields a difference of 232 seconds or 3.87 minutes. The wind holds until the fleet rounds “10A” and then begins to die (4 – 6 Kts.). We’ve all been there! What happens? With more than 1.5 miles to go the longer waterline boats pull away leaving the slower boats behind and the time difference between finishes can be as much as an hour. The problem is that with T.O.D. you’re stuck with that static 3.87 minutes whether it is blowing 15 or 5!

The only fix to the problem for TOD is to apply a course correction factor that mathematically lengthens the course for calculations but not in actuality. The spreadsheet as designed has that capability, however even that solution is flawed.

“Time on Time”:

Is a slightly more complicated system but is not static like Time on Distance. When calculating finish times with Time on Time a scratch boat is not used! The length of the course is not considered in the calculation. The amount of time that it takes a particular boat to sail the course and that boats time correction factor are all that are used in order to determine the boats corrected finish time. So how does it work?

Determining the boats actual time on the course is straight forward (and is also used in order to calculate the boats average speed in knots, displayed at the right side of the standings sheet.) Determining the correction factor is really nothing more than calculating the percentage difference between boats. For example; take the case of two boats one with a PHRF of 120 and the other with a PHRF of 90. By individually dividing both of the numbers (one at a time) into 100 we come up with time corrections factors of .8333 for the PHRF of 120 and 1.111 for the boat with a PHRF of 90. If you compare the numbers 1.111 and .8333 you will see that they are approximately 25% different from one another (.8333 is 25% smaller than 1.111.) If you compare the PHRF's you will see that there is a 25% difference also. In very simplistic terms the boat with the PHRF of 90 can be thought of as being 25% faster then the boat rated at 120. Notice that the faster boat (PHRF 90) has a correction factor of 1.111 and the slower boat (PHRF 120) has a time correction factor of .8333!  Now all that’s left to do is to take the boats actual time to complete the race and multiply it by the time correction factor for a corrected time for the boat. Note that the faster boat will have time added to its actual finish time while the slower boat will have time taken off of its actual finish. In this way Time on Time attempts to make up for dynamically, what Time on Distance does statically. The idea is that in the race talked about earlier, where the wind dies, all boats are affected equally by the diminishing winds, however because the correction factors are proportional, the theory is that Time on Time will attempt to adjust for conditions by proportionately adjusting the times.

Please note at the bottom left corner of the results sheet you will find the numbers required to calculate the Correction factors. They are; a global numerator (same for all calculations and is picked to keep the correction factors as close to “1” as possible) and a course correction factor that is added to the PHRF in the denominator. The course correction factor can also be changed to suit unique conditions.

I hope this explanation clears up any confusion as to what Time on Time can and can not do.

Thanks,

Jim Kline of “INKLINE” present time correction factor of 1,000