 The two caissons are 6.5 metres (21 ft) wide, and can hold up to four 20-metre-long (66 ft) canal boats. Watertight doors at each end match doors located on the upper structure and lower dock pit. Due to space concerns, where a normal hinged door would dramatically reduce the useful length of the caisson, vertically rising doors were chosen. The doors are raised from a recess in the base of the caisson and powered by a hydraulic lance when docked.
