Immediately behind the now-disused Estuary Control Tower lies the Small Boat Harbour, home to the fleet of five vessels belonging to Clydeport Operations Ltd. The oldest of the fleet is CLOCH, built by the Ailsa Shipbuilding and Engineering Co Ltd at Troon in 1968, as a pilot cutter for the Clyde Pilotage Authority. A smart little vessel, she is 66 feet long, and has a gross tonnage of 46 tons. Originally fitted with a single Rolls-Royce diesel, this was replaced with a Caterpillar engine some years ago. With the acquisition of new pilot cutters, CLOCH found herself surplus but was retained and fitted with equipment to maintain some of the navigation buoys around the estuary and River Clyde. Even those duties have been taken away from her, with TORCH fulfilling this important role, and CLOCH now spends most of her time lying at Greenock. The smaller vessel lying alongside CLOCH is the survey launch NEWARK.