Please Wait - Compiling Details.

<< Back to Query / Map page

Somerset Historic Environment Record


Site Name: Fussell balance lock trial site, Mells
Civil Parish: Mells
Part of:
PRN 23312Dorset and Somerset Canal
PRN 26100Excavation (2007), Balance Lock, Newbury Firs, Mells
Grid Ref: ST 736 503 (ST 75 SW)
  Show site on map (Requires Flash)
Image: Image of HER 15567 - Photo by Hunt, Derrick (14 May 2006)
  HER 15567 - Photo by Hunt, Derrick (14 May 2006)

Public access:

The public accessibility of this site is unknown or has not been checked. Please ask locally and do not visit without permission. [Information last updated on 21 May 2003]


Site of trials of James Fusel's patent balance or caisson lock, in 1802. The canal exists as earthwork, with towpath visible. The canal leads to the lock, which comprises a pit that would have housed the lock and part of a retaining wall. There are no remains of the mechanical structure. {1}

CONSTRUCTION The Balance Lock or "Boat Lift" was a large masonry chamber divided into two sections. It comprised two tanks full of water, each long enough to contain a boat. At the place where the canal stepped from one level to another, they were arranged in a pit, side-by-side with one end towards the upper canal and one end towards the lower. Running the whole length of the space between the tanks was a central wall, on top of which were iron wheels. These were larger in diameter than the thickness of the central wall so that chains draped over them hung down slightly clear of the wall on each side.

BALANCE The tanks were suspended from the chains by a pulley arrangement and the lengths of the chains were such that when one tank was level with the bottom canal, the other was level with the top. The tank weights were adjusted to be equal, so that they were in balance and easy to move up and down with little effort. They could be moved with a hand crank geared to one of the wheels or by adding or removing a little water from one of the tanks.

MOVING THE BOATS The ends of the tanks could be clamped against the ends of the top and bottom canals to make a water tight seal. Doors or sliding panels were then removed to allow a boat to be floated from the canal into the tank. As the boat entered the tank a certain amount of water would have to flow out to make room for it - the weight of this water would be exactly the same as the weight of each boat with its cargo, so the balance of the tanks would not be upset. With the boats in the tanks, the doors or panels were replaced to seal the ends of the canals and the tanks. The tanks could then move up on one side and down on the other so as to deliver the boats to their new levels.


1 An estimate of the dimensions of the Trial Balance Lock machine is 35 feet high, 24 feet wide and 30 feet in length.

2 The Trial Lock would have raised or lowered boats approximately 20 feet.

3 The plan was to raise or lower boats 40 or even 50 feet (or more). {2}

See PRN 26100 for details of an excavation undertaken in 2007. {3}


1 Site visit report - Ward, L SCC 14/7/02
2 Detailed records - Hunt, Derrick. Fussell's Balance Lock Description. unpublished typescript (05/2005) Copy in HER
3 Compiler comment - Bagwell, T [Talya]. Somerset County Council, Historic Environment Record (2/1/2008). Location: verbal or direct entry to database, no other records.

Record created on 18 July 2002

© Copyright Somerset County Council 2016