The handicap system used by the club for several events is the North American Portsmouth Yardstick (D-PN) with Wind Handicap Numbers (HC). This system is managed by US Sailing and is a pretty fair method that covers more classes than most. As an empirical handicap, it uses actual finish times of the first place boat in various classes all across the country to establish the handicap numbers.

When developing a handicap number, the Portsmouth Yardstick assumes that the first place boat in each class sailed a near perfect race for the conditions, all boats sailed the same course and experienced the same conditions, and all boats conform to class specifications and rules.

Portsmouth Numbers reflect the length of time boats will take to sail a common but unspecified distance. A boat assigned a D-PN of 80 will sail the same distance in 80 minutes as a boat assigned a DPN of 90 will sail in 90 minutes. The lower the number the faster the boat.

The Primary Yardstick is the Thistle, and a handicap number is based on how a given boat compares to it. Some performance variance with wind speed is accounted for by time-on-time systems, but scoring vastly different boats or boats with varying performance across the Beaufort Scale benefits from using Wind Handicap Numbers (HC). The Thistle is a stable performer across all wind speeds, and as such is given the same handicap across the Beaufort Scale.

Good race committee work has a great deal of influence on the results. Courses for handicap races should include fairly equal amounts of beating, reaching, and running.

When racing under any handicap system the most important things to do are:

- Understand the course
- Understand the relative performance of different boats
- Remember you are racing the clock
- Avoid crowds and dirty air

Corrected times are calculated using the equation:

CT = ET/(DPN or HC) * F

Where
CT is the corrected time, preferably in decimal minutes
ET is the elapsed time, preferably in decimal minutes
DPN is the Portsmouth Number
HC is the Portsmouth Number with wind factor
F is the Handicap Conversion Factor

Recommended  F = 100
F does not affect finish order

When using HC Factors, the Race Committee is the final authority on wind speed for each race. Beaufort Numbers (BN) are generally divided into the four major wind areas of 0-1, 2-3, 4, and 5-9. Some newer boats like the Melges 15 plane in lighter air than before, and have subdivided the second wind area (2-3) for each BN. The example below uses that specific case.

Jacomo Sailing Club has contributed to US Sailing's Portsmouth Numbers Committee for many years. Continued reporting from clubs across the county helps develop the next edition of the Yardstick Tables.

EXAMPLE:

With all boats sailing the same course, in wind of 9 knots (BN3) and a clock time starting at 0:00:00 the finishes are:

1:00:30 - MC Scow
1:00:25 - Melges 15 
1:06:55 - Sweet 16

Converting to decimal minutes results in:

60.50 - MC Scow
60.42 - Melges 15
66.92 - Sweet 16

Using the HC Factor at BN3 we get:



87.4 - MC Scow
86.5 - Melges 15
95.9 - Sweet 16

The corrected time of the MC Scow is therefore:

CT = (60.50/87.4)*100 = 69.22 minutes

The corrected time of the Melges 15 is therefore:

CT = (60.42/86.5)*100 = 69.85 minutes

The corrected time of the Sweet 16 is therefore:

CT = (66.92/95.9)*100 = 69.78 minutes

Converting back to clock time is unneeded, but results in:

1:09:13 - MC Scow
1:09:51 - Melges 15
1:09:47 - Sweet 16

Even though the Melges 15 finished 5 seconds before the MC Scow and 6.5 minutes before the Sweet 16, it lost to both on corrected time.  

Within the normal wind area for BN3, the Melges 15 would have beaten both boats by about 3 minutes on corrected time. Accurate wind readings, good course layout, precise timing, and orderly scorekeeping are essential to conducting a fair handicapped race.

Resources

North American Portsmouth Yardstick Table of Pre-Calculated Classes
Melges 15 D-PN Guide
North American Portsmouth Yardstick Handbook