Ardnacrusha Navigation locks – gateway on the Shannon to Limerick City and beyond

As part of the construction of Ardnacrusha Power station in the 1920’s, a two stage navigation locks was constructed to allow boats to travel down the Shannon, an essential waterway for the transport of goods up and down the country at the time. The ‘Nav locks’, as they are known, lower/raise the boats 100 feet in a gradual process over a period of one hour. The freight traffic has long since ceased and the traffic now comprises of pleasure crafts leisurely cruising the Shannon. Roughly, 300 pleasure crafts pass through the locks every year.

The locks comprise three large gates which weigh roughly 40 tonnes each. These large gates are lifted by winchgear housed over each gate. The electrical controls and equipment were installed in 1929.

On October 1st 2008, the Nav locks were closed to enable electrical refurbishment. This involved replacing all the switchgear, wiring, control equipment and replacing them with modern electrical equipment.

This electrical refurbishment took place over the winter to minimise disruption on the Shannon with May to September being the busy months. The various users of the Shannon, including Waterways Ireland and Inland Waterways, were consulted and updated on the progress.

In order to carry out this work the locks were dewatered and scaffolded out.

As well as replacing the electrical equipment new safety features, which were recommended by the External Dam Safety Committee - a panel of international experts who certify the Ardnacrusha dam - were added. These included:

• Electrical interlocking of the gates to prevent two gates being inadvertently opened at the same time.
• Differential Protection across each gate to prevent a gate being opened if the levels were not equal on both sides of the gate.

During the course of the work, various inspections of the mechanical equipment were carried out which resulted in a decision to carry out an additional program of mechanical work.

The work was managed and organised by Pat Hogan, Mechanical Supervisor and Jim McNicholas, Electrical Supervisor, Ardnacrusha. The work was carried out by the Electrical & Instrumentation technicians, fitters and dayworkers of Ardnacrusha station.

This successful project is part of ESB’s ongoing commitment and responsibility to the management of the Shannon Waterways and to navigation on the Shannon. ESB will continue to invest in the future in its water control assets. These will be driven by its long term asset plans as informed by the ongoing condition inspections being carried out.

The External Dam Safety Committee, who were in Ardnacrusha in April on an embankment inspection, were pleased to note that their recommendations were implemented and complimented the work done.

The first boat, after the refurbishment, went through the locks on April 14th. This boat was a Naval Service motorised eight-metre rigid-hulled inflatable boat on a charity run up the river Shannon. They travelled from Limerick City to the top of the Shannon in a new record time of 5 hours and 51 minutes. The photograph shows Ger Reid, the Nav locks attendant at Ardnacrusha, presenting a sponsorship cheque to a team led by Lieutenant Stuart Armstrong from the Irish Naval Service.

This was a complex project that involved a team effort from all the staff in Ardnacrusha who rose to the challenge to complete it in time for the boating season.