Merlin Rocket - and there were about 15 of them, getting rigged up.
Its a design I'd like to sail: it hull shape is better designed for those of us with long legs than a Laser (sorry Tillerman) and looks like it would sail fast without requiring 49er levels of athleticism.
What's really interesting about them is the Merlin Rocket was designed by Jack Holt right here in Putney commissioned by a syndicate at the Ranelagh Sailing Club, based to this day on the Putney Embankment.
So it should have no trouble with the, ah, challenging nature of sailing on the Thames. It seemed to be an interesting race, starting just after 3 pm and heading way down river out of sight.
Just under an hour afterwards the first boat was seen returning (above).
The rest of the fleet took a lot longer, with this colourful group about an hour later:
Alas this boat lost a lot of places by heading to shallows on the calm side of the river:
Updated: more photos just posted here!