AN ELECTRONIC system for monitoring underwater excavations is being used on a harbour improvement project in the Shetland Isles.
The Prolec Digmaster graphic display system was fitted to two hydraulic excavators to allow the position of their buckets to be monitored in real time during dredging of Lerwick harbour in preparation for the 1999 Tall Ships race. The 18 month contract for Lerwick Harbour Trust started in November 1997 and work includes refurbishing and replacing existing piles and the lengthening and strengthening of harbour quays.
Main contractor Herbosch Kiere Contractors brought in local contractor Garriock Brothers to carry out remedial work on the existing piles. To avoid damage to the piers during silt removal or backfilling, it was necessary to know the exact position of the bucket, its angle and depth underwater.
Prolec's system reproduces the bucket's movement in real time and provides the operator with a virtually instantaneous graphic display. Information is provided to a fixed and predetermined depth or batter line, allowing first time excavation of channels and banks without the use of sight lines and other temporary aids. The manufacturer says that the system allows dredging of harbours, berths and canals to be carried out without the need for divers.