Underwater “wing” provides Heesen Yachts with unparalleled efficiency.
From pods to jet drives, and from prop tunnels to resin-infused hulls and carbon-fiber superstructures; the quest to build faster and more efficient boats has led to some remarkable advances. We seem to be in a proverbial golden age of marine propulsion.
And the next big advancement might just come from an old design for something called a Hull Vane: an underwater wing that was invented in 1992, and first tested aboard a 58-foot sailing yacht bound for the America’s Cup. The Cup committee would go on to ban the appendage for providing the vessel with “an unfair advantage” in both speed and efficiency.
Fast forward to 2015. Van Oossanen Naval Architects recently dusted off their design for the Hull Vane to provide that once-banned efficiency to a 138-foot custom-built Heesen named Alive.
“The design brief for the new Heesen 42 meter called for a very fuel-efficient, comfortable, and spacious design,” says Perry van Oossanen of Van Oossanen Naval Architects. Knowing that fuel efficiency was essential to the owner, the design team saw the opportunity to incorporate their Hull Vane; a horizontal, underwater wing affixed to the aft section of a hull. Previously only used on container ships, the Hull Vane would make its motoryacht debut on Alive.
“The Hull Vane is a basically a fixed foil located below the stern of a ship. It reduces fuel consumption by optimizing the flow around the aft body of the vessel,” explains Bruno Bouckaert, global sales director for Van Oossanen’s Hull Vane.
“The force of running water across the wing of the Hull Vane creates a low-pressure pocket in between it and the hull,” says naval architect Pieter van Oossanen. “This effect raises [the aft portion of] the hull out of the water [thus reducing drag] and also propels the vessel forward, increasing its speed.”
After exhaustive tank testing and Computational Fluid Dynamics (CFD) calculations, the team of naval architects determined that a Hull Vane would in fact provide the necessary efficiency that the owner and Heesen Yachts were looking for.
During Alive’s sea trials, Heesen saw “24 percent [fuel savings] at maximum power and an average of 18 percent throughout the speed range,” according to Perry van Oossanen. But not everything about the Hull Vane’s performance was as expected, “It was not found initially but after quite a lot of work: The top surface of the Hull Vane is a low pressure region that sucks down any high waves that are in that location. So the vessel has less wave resistance.”
In other words, Alive’s pitch in head seas was dampened.
According to Perry van Oossanen, it’s easier to incorporate a Hull Vane into a new boat his firm has designed, but he further explains that the device can be mounted on and provide enhanced efficiency to an already built “medium-speed” (12- to 18-knot) yacht.
“For new vessels you have the option of reducing the propulsion power, which in itself is a cost savings which offsets the cost of the Hull Vane. But from an installation standpoint, there is really no difference [between an old and new boat],” says Perry van Oossanen. “We were even able to install a Hull Vane on a ship while it was in the water, without having to dry-dock it.”
In most cases the underwater wing is built from steel and mounted at the stern of the hull, but it can also be built right into the bottom of a hull, which was the case with Alive. It can also be built from aluminum or another composite material if weight becomes a structural issue. Van Oossanen Naval Architects claims that once the Hull Vane is installed, the only maintenance needed is a good coat of antifouling paint. “Since there are no moving pieces on the Hull Vane there are no maintenance costs.”
Heesen’s recent test data proves one thing: Once filed away and nearly forgotten, the Hull Vane is alive and well.
- Builder: Heesen
This article originally appeared in the March 2015 issue of Power & Motoryacht magazine.