1. Drive boat into lock
2. Tell lockstaff you need a visitors licence
3. Come and buy licence
4. Leave lock.
Job done.
Have a read of this ...
http://www.environment-agency.gov.uk...ing/31609.aspx
If you then download the 3rd PDF down , it has a conversion chart of feet to inches on page 5 and on page 6/7 it has the prices for visiting boats ( daily rate , 15 day rate and 31 day rate )
All we'd ask when you come upriver , especially being a RIB is that you take it easy , the river is a very different place to the tideway and the wash can be a pain ( even if you are travelling at the correct limit sometimes )
See you soon.