Portsmouth yardstick
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The Portsmouth yardstick (PY) or Portsmouth handicap scheme is a system of handicapping used in yacht racing and dinghy racing. The yardstick numbers allow dissimilar classes of boats to be raced against each other: the aim is to cancel out the inherent advantages and disadvantages of each class of boats, and provide a common time that represents the skill of the crew. The Portsmouth numbers are administered in the UK by the Royal Yachting Association, based on annual input from a large number of affiliated sailing clubs. In the United States it is administered by the Portsmouth Numbers Committee, using similar methods. While the two systems are similar, the US version uses handicap numbers scaled to 100, while the UK scale changed to a scaling of 1000 in the 1990s.
Each class of boat is assigned a PY number, with fast boats having low numbers and slow ones high numbers - so, for example, in the case of two dinghies, a 49er might have a UK PY of 747 while a Mirror has a PY of 1386 (these are the actual PY numbers for 2003, but note that adjustments are made each year).
The handicap is applied to the time taken to sail any course, and the corrected time can be used to compare widely different sailboats on even terms. PY numbers are continually updated with empirical data from race results worldwide. Numbers are provided for differing wind speeds (when the data are available), plus a composite number that can be used when the wind speed is variable or unknown.
In a race involving a mixed fleet, finishing times can be adjusted using the formula:
- Corrected Time = Elapsed Time x Scale / Handicap
where Scale is 100 for US numbers, and 1000 for UK numbers, and Handicap is the handicap for the given class of boat. Each boat's time is adjusted with the formula, and then the adjusted scores are compared to determine the outcome of the race.
For example, a PD Racer (a semi-open homebuilt class, and the slowest listed boat) has a US handicap of 140, and an A Scow (the fastest listed centreboard boat) has a US handicap of 61.8. If an A Scow takes 1 hour to finish a given course, and a PD Racer takes 2 hours, the handicapped times are:
- A Scow: 1 hour x 100 / 61.8 = 1.62 hours
- PD Racer: 2 hours x 100 / 140 = 1.43 hours
So the PD racer, although it took twice as long to finish the course, would be declared the winner. Numbers in the UK handicapping system would yield similar results, though some slight variation is to be expected due to variations in the race data used to compile each handicapping chart.
