The Portsmouth Number System
At HLSTC, as at most other sailing clubs, we aim to provide a fair racing environment by using the RYA's handicap system.
There's quite a wide range of performance across the various dinghy classes, from a superfast but tricky boat like the 49er, across to a slower but more manageable training boat like a Tera Sport. Of course the extent of the difference isn't the same all the time - it depends on the conditions, and also quite a lot on the location. But we need a measure of the typical difference to use in our races.
What the RYA does is to collect thousands of race results each year, from clubs around the country, and from this data it works out the differences between the classes across all the races. It takes account of the different locations and conditions, and arrives at a set of figures representing the relative performance of each class. These are called Portsmouth Numbers (PNs).
A PN is a time measurement (not a speed), so a faster boat has a smaller number, and a slower one a higher number. They represent the time that each boat would take to sail a notional course, assuming typical conditions and normal skill on the part of the helm/crew. The range is from around 800 to 1500 or more. Most of the boats racing at Hawley are in a narrower band between 1000 and 1200 roughly.
The RYA's description of the system can be found HERE, and they also have links to the latest available number lists.
How we use the system
The RYA's update to the PN list usually comes out in the first quarter of each year. They say that these figures are only advisory: clubs are recommended to make adjustments as appropriate to suit local conditions. In recent years we have used the figures as they are for most classes, but for the few boats that are rated below 1000, we apply a correction, because our conditions don't allow the fastest boats to be used to their full performance. We start using the new numbers as soon as possible after release, usually at the beginning of the next series.
We have two different kinds of races, applying the PNs in different ways. We refer to these as "handicap" and "pursuit".
We use the one called "handicap" for most races. In this one, we start all the boats at the same time, and get them all to sail over the same distance - the same number of laps of the course set out. We record the time that each boat takes to cover the distance, then scale their time according to their PN, to arrive at a "corrected" time. Finally we sort all the corrected times into order, and the boat with the shortest time is the winner.
The "Pursuit" style is used less frequently. With this one, we apply the handicap by letting each class sail for a different length of time, proportional to their PN. So all boats "should" cover the same distance in the time allowed; but some will have done more, some less. We stagger the start times for the different classes, calculating them to make the finish time the same for all classes, and when this time arrives, we signal the finish, and find out who has sailed the furthest.
