Handicapped fleets are handicapped using ratings assigned by the Sandpoint Sailing Association. Valid PHRF-NW ratings are also accepted. Races are handicapped using time-on-time scoring with the Time Correction Factor (TCF) calculated as follows:
TCF = 700 ÷ (550 + rating)
The rating is the yacht's assigned handicap rating.
The numerator, 700, is called the A factor. The 550 in the denominator is called the B factor. The A factor is simply a scaling factor and it has no effect on the placing of yachts after scoring. The A factor is typically set to value equal to the the B factor plus the average handicap rating in the fleet. When done this way, the TCF for a yacht rated at the average rating is one, so that yacht's corrected time is equal to her actual elapsed time.
SSA's formula is based on an average rating of 150. For a yacht rating 150, its TCF is 700 ÷ (550 + 150) = 1. To calculate the yacht's corrected time, its elapsed time is multiplied by the TCF, so in the case of yacht with a handicap rating of 150, its corrected time is equal to its elapsed time. Again, the A factor has no effect on the outcome of the race, but the closer it is to a yacht's rating plus the B factor, the closer the yacht's corrected time will be to her actual elapsed time.
The B factor, on the other hand, must be chosen carefully as it can impact the scoring. US Sailing recommends a B factor of 480 for heavy air or all off-wind races, 550 for average conditions and 600 for light air or all windward races. SSA uses US Sailing's recommendation for average conditions as it seems the fairest given our typical conditions.