A tall purpose built steel structure is positioned against the quay wall using a crane, water is pumped out of the chamber formed between the limpet dam and the quay wall, with the dm held in position by external water pressure.

The secret of the John Martin limpet dam’s success is the design of the seals, which has been developed over a period of 18 years. These provide a reliable watertight junction between the dam and the quay wall as well as across the lock bottom and gate cill.

Referring to the Galdstone Lock limpet dam, John Martin’s construction manager Adrian Macdonald said, ‘There are an infinite number of uses for limpet dams but with a working depth of 16m and a width of 7m, this is the largest we have ever built.

‘A more typical use for our limpet dams would be for inspecting and maintaining quay walls, sheet piles or tubular piles. On this visit to Liverpool we are replacing the pintles in two of the locks intermediate gates. We replaced he first pintle at the beginning of this year and we’ll be moving the dam to the other side of the lock chamber. As there must be no disruption to shipping, the dam is designed to fit within the gate recesses in the dock walls. We are working 24 hours a day however, so when a ship passes through the lock the dam stays in position but all personnel are evacuated for safety reasons.’

Over the next two years the inner and outer lock gates will also be refurbished as well as a major planned facelift for the six 460 ton gates themselves.

Nuttall returns to Seawork International this year, where is well as exhibiting, the company will also sponsor the Port Engineers’ Luncheon.