The Portsmouth yardstick (PY) or Portsmouth handicap scheme is a system of handicapping.  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. Portsmouth Numbers are continually updated with empirical data from race results worldwide.  in the United Kingdom the Royal Yachting Association, administer the scheme.

Each class of boat is assigned a "Portsmouth Number", with fast boats having low numbers and slow ones high numbers. In a race involving a mixed fleet, finishing times can be adjusted using the formula:

• Corrected Time = Elapsed Time × 1000 / Handicap
•  
• The club broadly follows the RYA but adjusts some handicaps based on our experience of classes in our conditions. As a club we submit our race results to the RYA to help them refine the handicaps.
•  

Current Portsmouth yardstick data can be found at the RYA's website.  Click here to open a PDF version of the 2010 PY numbers.