After proof of concept, Lutra Marine formalised the design and built a quarter scale prototype of the new patented Cutter Head unit for testing at the COAST lab facility at Plymouth University. Using the 35m sediment flume, the scaled unit was tested in sand in a variety of currents and depths of water, which proved the concept and design in a test environment. During this initial test, the advantages in efficiency of the unit became clear as it was extracting 0.06m3 of material in 60 seconds of run time whilst achieving a flat bottom and side to the cut. Sediment detectors were placed one and two metres downstream of the Cutter Head. The mean stream was 1knot, this increased to three knots in the vicinity of the cutter head due to the venturi effect.As can be seen from the two traces on the graph below, it was not possible to detect when the equipment was operating.
Whilst raising equity investment, we undertook R&D testing with both submersible and surface mounted pumps, Unit shape, the modular sections of the unit and had discussions with various South West ports to fully understand the industries needs. During this time, Lutra Marine fine-tuned the design for the full-scale prototype taking on board the feedback we had received from port authorities and companies involved in the marine industry. Lutra Marine worked with a commercial port in the South West to further develop the design by testing the scaled prototype in four different types of sediment (Sand, Mud, Silt and Shale) that were present in the port.
Following initial investment from the British Design Fund in July 2019, a full-scale prototype was designed and built. We worked with the port authorities in the active port of Hayle Harbour on the North Cornish Coast, to test the full sized Cutter Head.
Using a 13-tonne excavator, the Cutter Head was tested off the beach in the Hayle estuary, with the dredged material being pumped into the middle of the stream to be washed out to sea. This test enabled Lutra to validate the results of the initial trial at Plymouth University as it delivered an extraction rate of 100m3 per hour and delivered the same flat bottom and side walled cut. For this test the equipment was run off the hydraulic power supply from the excavator, though for the production units this has been switched to an electric supply to mitigate the environmental factors of burst hydraulic pipes and seals, as well as to increase the versatility of the equipment to enable it to work with any excavator or similar plant. In this test we used a 50kVa generator to power the 6-inch submersible pump mounted to the Cutter Head unit via Lutra Marine’s mixing unit. The switch to an electric power supply on the unit also means that the cutter head can be powered off the same generator as the pump, reducing the need for costly hydraulic linkages which can leak and pollute the surrounding areas.
In February 2020, Lutra Marine held a demonstration of the equipment to interested parties at Hayle Harbour Authority. After the demonstration, we held a short presentation on our equipment followed by a Q&A. We received extremely positive feedback from those in attendance, stating that the equipment is move versatile and can achieve more than other current dredging equipment is unable to do. The main appeal of our Cutter Head was the precision we could achieve, reaching areas other could not with a flat and even bottom and sides, the speed of the equipment and its ability to work in water as low as 60cm. Meaning less time for the marina/harbour etc to be out of use and finally the environmentally friendly nature of the system.