DAMEN Magazine #5

Unique dual-purpose tugs for South America

Published in category: Harbour & Terminal

At the start of 2017, Baggerbedrijf De Boer B.V. (Dutch Dredging B.V.) placed an order for two customised, special-purpose tugs, to be built at Damen Shipyards Hardinxveld in the Netherlands. The order went through its subsidiary De Boer Remorquage SARL, with the tugs needed for a 10-year contract with Grand Port Maritime de Guyane (GPM-Guyane) in the ports of Cayenne and Kourou in French Guyana. Their primary functions will be assisting vessels entering and leaving port, and rendering help in the event of emergencies including fire-fighting. However, they will also be equipped for an important, and unusual, secondary role. That is – dredging!

Dutch Dredging is a medium-sized, family-owned business based in Sliedrecht, the Netherlands. Founded around 50 years ago it now employs 190 people and over the years has expanded out of its home market. Today it operates across Western Europe and in South America, the Middle East, Africa and New Zealand. Its fleet currently numbers 27 vessels ranging in size from small survey vessels up to trailing suction hopper dredgers in the 70 to 100 metres class.

The company has been delivering primarily maintenance dredging services in French Guyana for the past 15 years. However, a new contract signed with GPM-Guyane in 2016 introduced towage operations for the first time, and so the company formed De Boer Remorquage SARL, a new joint venture with IJmuiden-based tug experts Iskes Towage & Salvage, to supply this new capability. From 2016 to 2017 this will be performed by conventional tugs, but these will then be replaced by the new, dual-purpose vessels.

The dual-purpose concept arose as GPM-Guyane was aware that specialist dredgers or tugs would not be fully occupied given the anticipated workloads for each activity. It therefore requested in its tender that designs be investigated that combined both dredging and towage in individual vessels. The tender contained a list of towage specifications that included draught, bollard pull, speed, and Fi-Fi capabilities to meet the towing requirements of the ports in Cayenne and Kourou. For dredging, the stated objective was that the vessels should also be able to maintain the existing harbour and channel depths.

Damen_WID_2915_performing_water_and_air_injection_dredging

The design process was very much a joint effort. Dutch Dredging contributed its knowledge of the unique technique of water and air injection dredging that it has built up over 20 years. Its experience over the past 15 years of operating in the specific conditions of French Guyana was also very relevant. With its many years of operational experience in harbour towing and assistance, Iskes Towage & Salvage provided valuable input for the towage element of the design and build process. GPM-Guyane contributed to the development of the designs via its consultants, Hydro GC and Earthcase. They checked and approved the designs, and helped optimise the dredging-towing balance so as to achieve an equilibrium within the given specifications.

The result was the unique WID 2915, the first vessel ever to combine full towage capabilities together with dredging using the Air and Water Injection Dredging (AIRSET) method. This is a relatively new dredging technique that is particularly suited to smaller, tidal harbours. It works by fluidising the sediment layer using water jets and injecting air to bring the sediments to the surface where the air can escape and then allowing the sediment to flow horizontally, out of the harbour or channel using natural processes and forces. This removes the need for the physical extraction and transportation of the sediment and causes much less disruption to other traffic using the ports.

The second vessel being supplied under the contract is the smaller ASD 2310 SD (Shallow Draught) tug. This is also a modified design, and will be fitted out to operate the equipment needed for bed-levelling, as well as carrying out surveying activities. As these two tugs will be the only support vessels available to either port they will also be used for the transportation of equipment and cargo, up to container-sized loads.

De Boer Remorquage SARL, assisted by Iskes Towage & Salvage and Baggerbedrijf de Boer, will operate the tugs and employ and train a number of local staff and crew in the skills required to man and maintain workboats. Iskes already operates a number of Damen vessels, including three ASD 2810 Tugs and a recently delivered ASD 3212.

Together these innovative tugs will deliver an unusual combination of capabilities that will allow both the end client and the operator to minimise their capital expenditure and operating costs without any loss of effectiveness or efficiency.

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