Feature 2 | ADVANCED HULLFORMS
Sea Axe hullform attracts growing interest from military users
Te Axe Bow or ‘Sea Axe’ concept for monohull vessels, which was developed and introduced approximately five years ago with great commercial success is attracting a growing number of customers in the military and paramilitary markets.
L
arge numbers of Sea Axe vessels have been built and are on order for applications
ranging from
crewboats in offshore industry to super yacht tenders to pilot craſt and high-speed patrol boats for the military. Damen Shipyards uses the Sea Axe
brand for designs that are based on the Axe Bow concept, which was originally developed by Lex Keuning at Delft University of Technology (TU Delſt). Te Sea Axe, which has a proven design history behind it, was the successor to the Enlarged Ship Concept that TU Delſt developed with Damen in 1995. The idea behind the Enlarged Ship
Concept was later taken a step further in the Axe Bow Concept. In co-operation with the Royal Netherlands Navy, the US Coast Guard and the Maritime Research Institute, TU Delft and Damen carried out a long-term research programme to determine the merits of the new hullform. They found that the Axe Bow makes
a huge difference to the accelerations experienced by a vessel. Te very deep and high straight bow, which does not have any flare but has a ‘V’ shape, gives the Axe Bow very soſt ‘suspension.’ Full-scale measurements confirmed the
results of model tests which indicated that the highest vertical acceleration peaks are approximately 80% lower when compared with conventional high-speed craſt. Although development of the Axe
Bow was purely focussed on a vessel’s improving seakeeping characteristics, model tests showed a significant reduction in resistance over conventional high-speed designs: 10% in flat water, 18% in Sea State 3, 22% in Sea State 4. It was therefore predicted that similar fuel savings should be found at full-scale. One of Damen’s major customers,
22 Damen is working on a number of military designs based on the innovative Sea Axe.
the Mexican offshore operator Naviera Integral, was asked to carry out a comparative fuel measurement on a 50m Sea Axe Fast Crew Supplier and a conventional fast supply vessel. The vessels were of similar size and capacity and have exactly the same propulsion plant. Even though the Damen Sea Axe vessel had a steel hull it still achieved average fuel savings of 18% over the fully aluminium craſt.
Military/paramilitary versions At the time of writing, Damen had delivered around 30 Sea Axe monohulls and large numbers were under construction. Speaking to Warship Technology in early September, Jaap Gelling, Product Director High Speed Craft at Damen Shipyards Gorinchem, said the company has recently concluded a number of deals for military/ paramilitary versions of the Sea Axe. “We have just delivered two Sea Axe Fast Crew Suppliers 3307, customized
as ‘security/guard vessels’ to Special Vessel Services,” Mr Gelling told Warship Technology. “Te vessels will accompany an offshore platform delivery from Sri Lanka to Tanzania, where the platform will be guarded by the vessels.” “The first Sea Axe Stan Patrol 5009
for Cape Verde is being outfitted at the moment,” said Mr Gelling. “Tis vessel will be delivered in December, and we are close to selling more Sea Axe FCS 3307s, 5009s and 6711s for security/guard vessel applications.” The latest evolution of the Sea Axe
concept, the Twin Axe, brings many of the advantages of the new hullform to twin-hull craſt and allows for a more stable platform within the 24m loadline. Compared with conventional
catamarans with the same displacement the new concept reduces peak accelerations by up to 75%, has reduced calm water resistance of up to 15% and reduced added resistance in waves of up to 60%.
Warship Technology October 2011
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