Quite a good
Wikipedia entry . In the UK, the RYA gathers data from sailing clubs to arrive at PY numbers, which get adjusted every year. They're more reliable for dinghy races - for cruiser racing, most clubs use their own variants for known boats and people, usually based on previous race results.
For example, at my last club, I had a PY number of 1050, when the RYA one is 1069 (and the PSSA one 1063). I had a low number because I'd done well in some light wind races, and the other boats hadn't. But I think it's pretty impossible to have a "fair" rating system for widely different boats across all weather conditions.
On the current RYA list , the Seal 22 has a PY number of 1215, the PSSA number is 1140.
Geoff
Parker 21 / 18 Dawn