This “blade” hull derives its name from the knife-like bow appendage devised by Arrabito Naval Architects.
The sharp-edged appendage, instead of being tacked on to the bow like a conventional bulb, is integrated into the hull form and projected backwards for a third of its overall length.
By minimising the longitudinal curvature of the waterlines, the entry is dramatically refined and the overall effect is akin to cancelling out wave formation at the bow, much like a wave-piercing hull.
This significantly reduces the bow wave resistance and total resistance, while the aft portion of the hull is designed to provide ‘fast displacement’ hydrodynamic lift and a partial planing effect that extends the speed range, while also resisting the undesirable motions associated with conventional semi-planing or planing hulls.
Estimates are based on tank tests conducted in 2007 at SSPA in Sweden on a 62m version financed by a prospective owner. Four different models were used for comparative towing tests, but also to measure sea keeping, streaming and propulsion. The primary model featured both blade and modified bow section; the second without the blade; the third was a hard chine semi-displacement hull; and the fourth was a hybrid of a hard chine hull with the blade.
The results for the primary model showed a reduction in total hull resistance of between 13 and 22 per cent over a range of speeds from 15-35 knots (and produced positive performance results up to 33 knots).
Sea conditions proved to have little effect on resistance and sea keeping.
In fact, Arrabito was pleasantly surprised to learn that the ‘blade’ and forward shape of the hull had a significant damping effect on pitching motions, helping to reduce vertical acceleration and keeping the foredeck dry.
A complete series of tank tests have also been carried out for a 36m yacht (originally to be built by Cantieri di Pisa) with comparable results.
Tank testing on latest 45m Blade model were done in 2012 and predictions said that a 440 GT vessel will consume around 68 litres of fuel per hour at ten knots when powered by MTU 16v 2000 M94 main engines (two x 1,939kW @ 2,450rpm) for a range of approximately 3,500nm.
Furthermore, the maximum speed is about 13 per cent faster than a conventional displacement hull of comparable gross tonnage, displacement and power installed.