Naval architects have long sought to decrease the resistance of their superyacht hulls with clever design tricks. One of the earliest developments was the bulbous bow, which changes the wave pattern of the hull to reduce wave-making and resistance, thereby increasing efficiency. Imagine, however, if there was a moderately simple bolt-on solution that could offer improved efficiency for both new and existing yachts. Enter the Hull Vane.
Developed by Van Oossanen and Associates naval architects in The Netherlands, the Hull Vane represents a decade of research and refinement. Effectively no more than an underwater foil at the stern of the yacht, it claims significant increases in efficiency – and Heesen’s recent 42m superyacht Alive is a living testament to the technology.
Tailored to the individual superyacht, the foil is fixed at the aft end of the hull – after the rudders and the main underwater body – creating lift and a resulting forward thrust while also reducing the stern wave.
The benefits are obvious. “The main effect is forward thrust,” says Bruno Bouckaert, commercial director of Hull Vane. “Then you have the secondary factor in that it reduces waves. The third factor is it reduces the running trim – also advantageous with a bulbous bow. Fourth, it dampens pitching motion, which not only gives another two or three per cent efficiency but also greatly increases comfort.”
While the vane is a fixed attachment that can be retrofitted to any suitably shaped hull, the biggest advantages come when specifying a Vane from the outset. “The Heesen 42m achieved the biggest savings we have seen so far, from 20 per cent at 12 knots to 23 per cent at 14.5 knots,” Bouckaert says, “therefore it needed smaller engines.”
That means less space not only for the mechanical installation but also for exhaust and ventilation ducting, which in turn means more of that precious gross tonnage freed up for use in the interior. Not every hull is suitable for a Hull Vane or foil, but more typical displacement and semidisplacement superyacht hull forms – where water flows up the rise of the buttocks from the lowest point of the hull – are ideal. With the concept now proven, and with the Vane offering anything from 10 to 23 per cent efficiency savings, it’s no wonder that several yards and some owners are in negotiations for the system. “For new yachts we think it will become as common as the bulbous bow,” Bouckaert concludes.
While we’re on the subject of reducing hull resistance, Dutch company Ship Motion Group claims to have perfected a standardised, retractable propulsion system for performance superyachts, whether the yacht has a carbon or aluminium hull.
The lightweight Retractable Propulsion System (RPS) had its first superyacht installation in 2012 aboard Baltic’s 45m high-performance superyacht Visione and has since been added to another Baltic performance build. In addition to the obvious benefits for sailing, the system has been designed to offer maximum propulsion efficiency, which in turn reduces the power requirement to achieve the same speeds under engine as a conventional sail-drive or shaft and prop system. And reduced power means smaller engines, which means lighter weight, which means faster sailing…