We left Peterborough Marina around 0930, lock 21 is a very special lock on my trip. It is called Peterborough Lift Lock, it’s not a conventional lock design. (here are some facts I learned about it from Lock Master Jon) The lock has two identical bathtub-like ship caissons in which vessels ascend and descend. Both caissons are enclosed at each end by pivoting gates, and there are pivoting gates at the upper and lower reaches of the canal at the junctions with the caissons. The gates on the caissons fit into slots on the gates on the reaches, so that they open in unison. Each caisson sits on a ram, the shafts for which are sunk into the ground, are filled with water, and are connected with a pipe that has a crossover control valve. The caissons are guided up and down on either side by rails affixed to concrete towers. No external power is needed, The lift lock functions by gravity alone using the counterweight principle. One caisson always ascends and the other always descends during each locking cycle.
check out my video, its long even though its running at 4x normal speed so just enjoy the lift lock with JJ Grey & Mofro “Blackwater” 5.5min