OPERATIONS

During sea trials on the river Clyde an average speed of 12.687 knots was achieved by the ship in the loaded condition. Normal full speed whilst in service was between 10 and 12 knots, depending on tidal conditions and wind speed. The M.V. "Gardyloo" berthed in the Edinburgh dock at Leith, alongside the sludge holding tanks where the sludge from Seafield sewage treatment works was pumped. This sludge came from the city of Edinburgh, via sewer pipes, and by road tanker, from outlying sewage works, such as North Berwick, Dunbar, Haddington, South Queensferry and others in East and West Lothian. As the sludge was loaded, saltwater ballast was pumped out, so that at no time did the vessel sink below the official Plimsoll marks. When the loading was complete (approx. 30-45minutes) the loading pipes were flushed with fresh water then disconnected. During loading of the sludge, by gravity, exhausted gas was forced through the enclosed system to a filtration unit on the dockside which eliminated all odours. When all the loading valves had been closed and cargo hatches secured, the ship proceeded through the dock system and into the locks where the vessel was lowered to sea level and the voyage to the North Sea dumping ground commenced. Two areas in the North Sea were licensed, by the Department of Agriculture and Fisheries, for controlled sludge dumping. One was off St Abbs Head within a one nautical mile radius of position Lat. 56 degrees 04.5minutes N, Long. 002 degrees 07.25 minutes W. and the other off the Bell Rock lighthouse within a one nautical mile radius of position Lat. 56 degrees 25 minutes N. Long. 002 degrees 10 minutes W. The voyage from Leith to the St Abbs dump was 37 nautical miles and to the Bell Rock dump was 42 nautical miles. Fifteen minutes prior to arrival at the dumping area the cooling system for the main engine and auxiliary machinery was changed from sea suction to internal cooling tanks. This prevented dumped sludge from entering and blocking the coolers. On arrival at the dumping area eight large dumping valves were opened to allow the sludge to discharge, by gravity, through pipes in the vessels bottom. Each pipe has a diameter of 500mm. The discharging rate was approximately 6,000tonnes/hour. On completion of dumping, which took approximately 20-25 minutes, the eight dumping valves were closed and four ballast tank inlet valves  opened to allow 1,188 tonnes of sea water to free flood into the four main ballast tanks. When the ballast tanks were full, approximately 20 minutes, the ballast valves were closed, the cooling system returned to sea suction and the vessel headed homewards towards Leith.