Settlement in the tunnel lowered the headroom, and the towpath subsided between the water in places. As a result, an electric tug was introduced in 1914 at a cost of £1,563 (). It was capable of pulling 30 boats at a time through the tunnel, at a charge of 6d a boat (). A second tug being added in 1931. The tug operated until 1954 when system of 3× fans was constructed at the south portal to improve ventilation for diesel-powered craft. While boats are within the tunnel an airtight door is shut so fresh air is constantly drawn through the tunnel. The fans protect boaters from the harmful build-up of diesel fumes. Modern journey times are now about 30–40 minutes.