Sailing boats come in many different shapes and sizes, designed for different purposes. A family plaything will be spacious, stable and easy to sail at the expense of performance; a high performance racing dinghy will be extremely fast, at the cost of being more unstable and more complex to control.
Naturally in a race between two such boats with similarly skilled crews, the racing boat would win. So how do you race different classes of boats, if they have totally different characteristics?
The Portsmouth Yardstick was introduced as a handicap system for boats to allow times to be compared across classes. Each class has a number, known as its Portsmouth Yardstick or PY number, which represents its speed; a fast racing boat will have a low number, while a slower boat will have a higher number.
Using this number and the total race time of a competitor, a "corrected time" can be calculated by...
Elapsed Time (seconds)
---------------------- x 1000
This time can be compared with the corrected times of the other competitors to determine the results of the race.
Imagine a race between a Laser and a Mirror dinghy. The laser is a modern, lightweight boat designed for racing; it has a PY number of 1078. The mirror, on the other hand, is a small boat designed for general purpose use and children; it is stable and easy to sail, but slow; it has a PY number of 1386.
The laser finishes the race in 71 minutes, and so has a corrected time of 3952 seconds. The mirror finishes in 89 minutes, with a corrected time of 3853 seconds. So despite the mirror crossing the line 18 minutes after the laser, it still wins with over a minute and a half to play with. This is a most satisfying feeling for those who sail slower boats, as they can be miles behind yet still win...
For pursuit races, the Yardstick can be used to determine the interval between different classes starting.
Some example PY Numbers
- 49er - PY 750 - Olympic two person racing boat
- Laser - PY 1078 - One man racing boat, also used in the olympics
- Enterprise - PY 1116 - Racing and cruising dinghy
- Optimist - PY 1646 - Very small boat for children; looks a bit like a bathtub...