Damen nozzles for ALP super tugs

Delivery of the four 300tbp anchor-handling tugs, scheduled between the end of 2015 and early 2016, will without doubt be of significant interest among the global towing community. ALP selected Ulstein for the towing vessels’ design (a new market for Ulstein) and a new marque, designated the SX157 featuring their patented X-BOW® was developed especially for the project. The tugs are being built by Niigata Shipbuilding & Repair in Japan.

Details of Damen’s order for the nozzles has provided an insight into the degree of engineering skill and precision required for just one component of this complex project that could easily be viewed as just another part of the overall process.

They will be the largest such nozzles manufactured by DMC using their spinning machine technique and the order was placed by Caterpillar Propulsion of Gothenburg (responsible for the complete main propulsion units) and involves design, engineering and production of the nozzles and head box sets. Propulsion for the 24,400bhp tugs will comprise a conventional arrangement of twin controllable-pitch propellers and rudders.

DMC will manufacture the ‘Optima’ nozzles using the spinning machine in their own plant in Jiang Yin, China. The novel manufacturing technique involves only one single weld and will have a very precise 5,050mm inside diameter to accommodate the 5,000mm diameter propellers. They will be larger than nozzles manufactured to date by DMC’s first spinning machine at their plant in Gdansk Poland. The nozzles’ 0.5 L/D ratio will result in a length of 2.5m, half their diameter.

In cooperation with the vessel’s designers and under Caterpillar’s auspices, DMC will also engineer the streamlined head box bodies, part of the complete nozzle construction. FEM calculations were used to assess the nozzles frequency profile in order to prevent amplification of frequencies from snowballing with engine and propeller. This has resulted in a relatively narrow head box and strut connection, but stiff enough to secure the frequency profile. DMC claim an edge over other nozzle manufacturers as they have the high computer power available within the Damen organisation required for this specific order.

By Peter Barker