Feature 7 | SURFACE COMBATANTS
The PS vessels have an interesting diesel-hybrid machinery configuration.
adapted for a new series of Sea Axe Fast Yacht Support Vessel with three Sea Axe vessels having been sold as yacht support vessels to date. Working closely with the Royal
former was considered to be good in flat, calm conditions but disadvantaged in a seaway, while it was judged that the speed of the PS was too low to derive significant advantage from the Axe Bow. As a result a traditional form has been adopted. The ship’s structures are being built from mild, rather than high tensile, steel, which will result in a cheaper but heavier displacement vessel overall. This decision reflects the aim of acquiring a relatively cheap, robust platform with good seakeeping capabilities. Active fin stabilisers will be fitted to improve seakeeping in higher sea states. Tis represents something of a departure given the Royal Netherlands Navy’s previous preference for rudder roll stabilisation. As highlighted previously in Warship
Technology, the PS vessels also have an interesting diesel-hybrid machinery configuration where a direct drive arrangement is supported by an electro-motor power take-in (PTI). The main engines take the form of a 5400kW/1000rpm MAN 12V 28/33 D
diesel, two of which drive Rolls-Royce five-bladed CP propellers through Renk Type ASL 85 double helical reduction gearboxes. Three 968kW/1800rpm Caterpillar 3508B generators (two in the aſt engine room and one in the forward machinery space) will supply electrical power (440V) to support ships services and low-speed electrical propulsion. Te ‘Sea Axe’ brand name is used by
Damen for designs that are based on the Axe Bow concept, which was originally developed by Lex Keuning at Delft University of Technology (TU Delft). Although still a relatively new concept in the naval sector, the Sea Axe already has a proven design history behind it, being the successor to the Enlarged Ship Concept developed at TU Delſt with Damen in 1995. Since its inception, moreover, the concept has been widely adopted in the offshore oil and gas industry, and in the super yacht market. Te pioneering Sea Axe design, first
applied on Fast Crew Supply (FCS) vessels for the offshore industry in 2006 continues to be a success and was recently
Artist’s concept showing Mai 1105, a new OPV for Romania with the characteristic Damen Axe Bow hullform.
Netherlands Navy, the US Coast Guard, Maritime Research Institute Netherlands (MARIN) and TU Delft, Damen conducted an extensive research programme to determine the merits of the Axe Bow concept and found that adopting the Axe Bow concept makes a significant difference to accelerations. Te very deep, straight bow, lacking any flare and ‘V’ shape, gives the Axe Bow hull much reduced accelerations with full-scale measurements confirming model test measurements that the highest vertical acceleration peaks are approximately 80% lower than on a conventional high-speed craſt. Although the focus of development of
the Axe Bow concept was on improving seakeeping, model tests also demonstrated a significant reduction in resistance over conventional high-speed designs: 10% in flat water, 18% in Sea State 3, rising to 22% in Sea State 4, with a consequent reduction in fuel consumption. A little over a year ago one of Damen’s
major customers, the Mexican offshore operator Naviera Integral carried out comparative fuel measurements on a 50m Sea Axe FCS and a conventional aluminium-hulled fast supply vessel built for the company in the USA. Te vessels were of similar size and capacity and had exactly the same propulsion plant, but event though the Sea Axe FCS had a heavier steel hull it demonstrated average fuel savings of 18% compared to the conventional aluminium vessel. Tere are now 22 Axe Bow vessels in
service and 20 under construction, and Damen was recently awarded a contract for a 50m Sea Axe patrol vessel for the authorities in Cape Verde. Damen’s close ties with Romania and the advantages of the Sea Axe hull concept have also seen another new design, a 66m Sea Axe offshore patrol vessel (OPV) capable of 22-20kts ordered by the authorities in that country. Due to be delivered in September 2010, Mai 1105 is a Damen OPV 950 design with a length overall of 66.03m, length between perpendiculars of 64.05m and displacement of 925tonnes. WT
34 Warship Technology July/August 2010
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