The Allocated Handicap (AHC) is the handicap used for the current race. For race 1, this handicap is allocated by the handicapping committee. For subsequent races, the AHC is the CHC calculated from the previous race in a series.
The Back Calculated Handicap (BCH) is calculated by the system and is the handicap that each competitor would have sailed to in order that all competitors finished with the same corrected time. For BCH the reference time will be that of 46% of the fleet.
The Calculated Handicap (CHC) is calculated by the system as a result of performance in the current race using the Top Yacht Exponential Handicapping System. It is the handicap that will be used for the next race.
For the calculation process, each BCH will be restricted to a maximum difference (higher or lower) from the current AHC of the race from which it is derived. This maximum is known as a Clamp. The BCH with the clamps applied is called the CBCH.
Provided that the Upper or Lower Limits are not exceeded, the BCH will be restricted by the clamps which are currently set at +/- 6% of the AHC to produce the CBCH.
The Exponential System does not use any data from previous races in calculating the handicap for the next race, it simply focusses on the current race.
AHC R1 set by the Handicap Committee
AHC R2 = 2/3 AHC R1 + 1/3 CBCH R1
AHC R3 = 2/3 AHC R2 + 1/3 CBCH R2 and similar for remaining races.
The proportions of AHC and BCH used can be altered in Top Yacht eg 1/2AHC + 1/2 BCH is used for Twilights.
During a series, boats typically have one great performance and some bad due to breakages, etc. Limits are a mechanism to accommodate these anomalies.
These function as follows:
Lower Limit: if the BCH is below this limit, the competitor is assumed to have broken something etc. and the BCH is not representative of a boats normal performance. In this case, the BCH for that race is ignored and the CHC will remain unchanged.
Upper Limit: if the BCH is above this limit, the full BCH is used with no clamp applied. Two or more consecutive BCHs above this limit are considered as improving performance. Thus the second and subsequent consecutive occurrences will use an amplified BCH in calculating the AHC for the next race.