Fast Displacement Hull Form (FDHF) is a rigorously tank-tested hull concept developed by Van Oossanen Naval Architects a decade ago, and is proving its worth in practical passages made by an increasing number of motor yachts and commercial vessels.
The firm’s founder, Peter Van Oossanen, is best-known for the controversial winged keel that helped Australia 11 wrest the America’s Cup off New York Yacht Club in 1983, after NYYC had held the “auld mug” since 1851.
So Van Oossanen has a proud history in honing underwater appendages, and their patented FDHF systems, which were pioneered by Heesen with great success, continue to attract clients, but they are not completely new.
The advance in Home is that, for a motor yacht kept below 500 GT and with a shallow draft enabling her to nose into lovely Bahamas anchorages, FDHF has been combined with hybrid power to produce a really unique, cost-efficient and at times silently-run vessel.
“Sea trial results were impressive”, said a Heesen spokeswoman. “Not only did Home easily exceeded her contractual maximum speed of 16.3 knots in the traditional diesel engine mode, but she also eclipsed expectations in her hybrid silent cruising mode.
“Thanks to two 127kW water-cooled DC electric shaft motors, she exceeded the predicted speed of 9 knots, with noise and vibration levels well below the specification levels.
“Home is not only ultra-quiet. She is extremely fuel efficient.”
At 12 knots, she has a fuel consumption of 98 litres per hour, excluding generators, and at 10 knots in hybrid mode, this further reduces to a staggering 45 litres per hour, which for a 50m yacht, displacing 295 tons and with a Gross Tonnage of 499, is an outstanding achievement.
“Heesen is renowned for its meticulous attention to weight reduction and Home is an effortless embodiment of this. Being lighter than predicted, she is the perfect demonstration of Heesen’s signature capabilities.
“This impressive performance is achieved with just two MTU 12V 2000 M61 engines of 600 kW each, which are smaller than those typically fitted on a yacht of this size.
“Once again, it proves the remarkable efficiency of the Fast Displacement Hull Form devised by Van Oossanen Naval Architects, engineered by Heesen’s in-house specialists, and perfectly executed by Heesen’s talented team of welders.
“Home has also exceeded her range predictions, logging an impressive 4,250 nm at 12 knots – 500 nm more than specified. This was achieved with a fuel capacity of just 45,000 litres, further underlining the remarkable efficiency of the Fast Displacement Hull.”
Interestingly, earlier studies showed that from an owner’s perspective, fuel efficiency was arguably not the key attraction in buying a hybrid system.
Eric van Mourik, Cost Accounting Manager at Heesen, said that “we attended the Electric and Hybrid Marine World Conference in Amsterdam and in Florida, and approached different suppliers. What emerged from this research was that, in a yachting context, the main advantage of hybrid propulsion was the enhanced comfort that the option of silent cruising provides.
“And Home is exceptionally quiet. In electric mode, the noise levels in the owner’s stateroom are an astounding 46 dB. To illustrate just how quiet this is, when the project was first presented at Monaco Yacht Show, Professor Barry Smith explained that 46 dB ‘is the sound of softly falling rain’.
“That is a sound we like, a sound that is comforting to the ear. Compare that to ordinary conversation at 60 dB, or a slightly noisy restaurant at around 80 dB,” explained van Mourik.
In the quest for quiet, some hybrid yacht systems use lithiumion battery banks, providing completely silent power, but initially Heesen rejected this, finding that the output was usually limited to providing loads at anchor.
Lots of batteries were also expensive, heavy and took up space, but Peter van der Zanden, Heesen’s GM of Design and Development, said they had reserved judgement until it was established how long hybrid owners would want to cruise in silent mode.
The vessel is quite a head-turner. Frank Laupman of Omega Architects is responsible for her striking profile. From her vertical bow and spray rails, to her stern, with its large fixed swim platform, wide sweeping stairs leading to the main deck, and floor-to-ceiling glass windows, Home is definitely unique.
Interior stylist Cristiano Gatto also worked closely with the owner to create an interior décor that boasts a sophisticated linear design, based on a two-tone palette. This theme gives a relaxed and bright feel throughout the whole interior, inviting the outdoors and spectacular vistas to feature centre stage from within.
Tasked with a design brief that asked for a straight bow and a generous use of glass, the exterior of Home, designed by Laupman, is characterised by her long waterline, floor-to-ceiling windows, and the dawn of a new design language.
The interior design of Heesen’s Home yacht for a client will be revealed in the second part of the feature, so do keep a look out for the story.
For more information please visit www.heesenyachts.com
Words Ross Wolfe | Images courtesy of David Churchill And Jeff Brown (Breed Media)