What's the speed limit on the Thames and where can I launch?
It depends where you are:
The non-tidal river, above Teddington Lock, has a speed limit of 8 kilometres per hour (that's about 5 mph or a bit over 4 knots). This part of the river is managed by the Evironment Agency, and a licence is required. See their web site or call 0118 953 5650 for more information.
On the tidal Thames between Teddington Lock and Wandsworth Bridge there is a speed limit of 8 knots.
Below Wandsworth Bridge there is no speed limit however the Port of London Authority like to make it clear that "safe speed depends upon the local area conditions and should be determined so that there is no risk of damage to persons or property. Causing damage is an offence, making the master of a craft liable to prosecution."
No licence is required on the tidal Thames.
There are a variety of launch places, mainly slipways that may not be usable at all states of the tide. Parking for your car and trailer may be difficult. It's not necessarily the easiest place to go ribbing, but it can be very rewarding. The BoatLaunch web site has a lot of useful info.
River Thames This Weekend
River Thames Cruising
River Thames Cruz
River Thames Licence Fees