The Tortoise Club is the alumni arm of OCBC, and it's purpose is both to recognise and celebrate outstanding OCBC athletes, as well as being the Boat Club's primary sponsor.
The club organises events in Oxford and London for its members (such as the Tortoise dinner usually in November). It is a British Rowing affiliated club, that its members can compete for in British Rowing races.
A copy of the Tortoise Club's constitution is available here.