Sweden

Candela Speed Boat 

Having come and gone more than once over the past 150 years, hydrofoils are all the rage again and here to stay this time. The latest technology has overcome many of the shortfalls of older systems, but are foiling superyachts feasible?<img src="https://photo-assets.superyachttimes.com/photo/308780/image/large-abca08ac22ef3c76d219eca23c4a28dd.jpg" data-gid="gid://syiq/Photo/308780">Over the past two decades foiling has taken off, literally and figuratively. It started with the innovative boards designed by surfers, followed by the specialist one-man classes like the foiling International Moths. Then came the high-performance sailing projects such as the 60-foot foiling trimaran l’Hydroptère, which broke the 50-knot barrier in 2008 and hinted at an exciting if highly specialised future for foils. But the idea of foils on mainstream leisure boats and superyachts has always seemed somewhat remote.<img src="https://photo-assets.superyachttimes.com/photo/308784/image/large-93508982c0f2307aa183db514c6f8972.jpg" data-gid="gid://syiq/Photo/308784">More recently, the advent of electric propulsion in tandem with the rising interest in foils, thanks largely to their adoption by the <a data-gid="gid://syiq/Company/6878" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="SailGP (Company)">SailGP</a> and <a data-gid="gid://syiq/Event/190" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="America's Cup 2024 - 37th America's Cup Barcelona">America’s Cup</a> sail racing programmes, has again brought foiling to the fore because they resolve a very basic problem. For boats with electric propulsion, or experimental hydrogen fuel cells in the case of the new <a data-gid="gid://syiq/Event/190" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="America's Cup 2024 - 37th America's Cup Barcelona">America’s Cup</a> chase boats, hydrodynamic drag means that displacement hulls and (to a lesser extent) planing boats struggle to attain a practical range for the given power-carrying capacity between charging. It is here that foils offer a clear advantage: if you can get your boat to emerge from the water and ‘fly’, you don’t need to worry so much about drag and the given power you are carrying in your battery banks can take you that much further. <img src="https://photo-assets.superyachttimes.com/photo/255101/image/large-3c47262ba3d15266b43994009e44c595.png" data-gid="gid://syiq/Photo/255101">“Our strategy is go faster to go further,” says Michael Jost, former Chief Strategy Officer at the VW Group who oversaw the start of the Group’s long-term transition away from fossil fuels. It’s a game plan Jost is employing with his new venture, eD-TEC, which has developed the all-electric eD-QDrive system. SilentYachts is coupling the system with a foiling 28-foot HYSUCAT multihull design to create a 40-knot electric boat that the catamaran builder claims still offers a range of 70 nautical miles.Electric avenue&nbsp;Across the spectrum, the combination of foils and electric drive systems is taking hold. Small boat builders such as Swedish brand <a data-gid="gid://syiq/Company/5799" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Candela Speed Boat (Company)">Candela</a>, <a data-gid="gid://syiq/Company/5737" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Enata Marine (Company)">Enata</a> in the Middle East, <a data-gid="gid://syiq/Company/6284" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Navier (Company)">Navier</a> in the US and Eldorado in the Netherlands, among others, are already building foiling leisure, passenger, water taxi and workboat vessels. The water toy world is alive with eFoil boards and the personal watercraft segment is also getting wise with projects such as the Valo Hyperfoil that adds retractable active foils to electric-drive jet skis.However, things get a little more complicated when it comes to larger craft. The advent of high-speed hydrofoil passenger vessels in the latter part of the 20th century was followed by a marked decline as the limitations of larger foilers became apparent – notably, the need for flat hulls with limited viability in bigger seas, and the potential for striking waterborne objects that could damage or destroy foils made from materials that were not as advanced as they are now.<img src="https://photo-assets.superyachttimes.com/photo/308788/image/large-eb9a1f3f86b23adca1520c7e78078250.jpg" data-gid="gid://syiq/Photo/308788">Considerable progress has been made in sailing with vessels such as the F50 used on the <a data-gid="gid://syiq/Company/6878" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="SailGP (Company)">SailGP</a> circuit, the new AC40 and AC75 yachts for the <a data-gid="gid://syiq/Event/190" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="America's Cup 2024 - 37th America's Cup Barcelona">America’s Cup</a>, along with the Ultime trimarans and IMOCA 60s. All these boats show how consistent 40-to-50-knot-plus performance is possible through the extreme application of surface-piercing foil technologies. Indeed, there has even been a crossover with sailing yacht projects like <a data-gid="gid://syiq/Company/6478" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="King Marine S.A. (Company)">King Marine</a>’s FlyingNikka&nbsp;mini maxi and sailing superyacht <a data-gid="gid://syiq/Yacht/10936" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Raven34.0m (111'7&quot;)Baltic Yachts2023">Raven 111</a> from <a data-gid="gid://syiq/Company/327" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Baltic Yachts (Company)">Baltic Yachts</a> that use foils to mitigate some of the displacement rather than making the hull fully fly. At the same time, however, they have also highlighted some of the limits to mainstream adoption.The foil wing tips are one. Even when the arms are folded under the hull for docking, they project more than two metres either side the yacht. Then there is the complex (and expensive) structural engineering needed to build and mount the arms into the topsides. Finally, there’s the sailing aspect, which requires precision and experience when powered up in foil-assisted flight.Practical limits&nbsp;For Seattle-based naval architect Paul Bieker, one of the world’s foremost experts on hydrofoiling, sailing foilers will always be limited by these constraints: “I would be surprised if fully foiling configurations find a significant place in mainstream, non-professional sailing yachts,” he says. “They require a lot of sailing skill and focus, high maintenance, expensive equipment, and they have a significant potential for personal injury.”&nbsp;Retractable foiling systems like the Dynamic Stability System (DSS) developed by Hugh Welbourn, Gordon Kay and Will Brooks, offer advantages such as improved righting moment, reduced heel and better motion in a seaway, plus more stability for big-boat, big-sea sailing. <img src="https://photo-assets.superyachttimes.com/photo/308786/image/large-d78769a2b71c292caceeab81b0112753.jpg" data-gid="gid://syiq/Photo/308786">“<a data-gid="gid://syiq/Yacht/10936" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Raven34.0m (111'7&quot;)Baltic Yachts2023">Raven</a> is not a yacht you could imagine relaxing in – it’s a balls-to-the-wall affair,” says Henry Hawkins, Executive Vice-President at <a data-gid="gid://syiq/Company/327" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Baltic Yachts (Company)">Baltic Yachts</a>. “But we used the DSS on the <a data-gid="gid://syiq/Company/327" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Baltic Yachts (Company)">Baltic</a> 142 Canova and it’s a completely different kettle of fish. There was a wish for a &nbsp;performance increase, but it wasn’t the driving factor behind the owner’s decision to install it.”The design demands of creating a full-flight vessel are, for the most part, incompatible with larger luxury yachts. Weight is a critical issue, for one, and while that can be overcome by adding larger foils, which in turn offer a greater aspect ratio and therefore greater lift, but there is an upper limit to the practical design of hydrofoils.“In general, the weight of a vessel scales with the length squared and the amount of lift that you can get off a foil scales with length squared – this reality means that there is a point where hydrofoiling gets more difficult with increased size,” says Bieker. “That said, the control of active hydrofoils tends to get easier with size because the actuators do not have to move as fast as they do in a smaller boats with smaller foils.”<img src="https://photo-assets.superyachttimes.com/photo/308860/image/large-a60ff05e451e2cee5403bcbd867c7901.jpg" data-gid="gid://syiq/Photo/308860">Bieker thinks there is more potential for moderate-sized foiling motor yachts: “The operating parameters for motor yachts are better defined and there is great potential for improving fuel consumption and comfort,” he says. “That said, they will still be significantly more expensive than non-foiling vessels.”Romain Ingouf is Technical Director at Artemis Technologies, a maritime engineering firm that emerged out of the Artemis Racing team that competed in the <a data-gid="gid://syiq/Event/190" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="America's Cup 2024 - 37th America's Cup Barcelona">America’s Cup</a>. The Belfast-based company has partnered with Condor Ferries to develop the 24-metre Artemis EF-24, a commuter ferry equipped with electric eFoiler propulsion able to carry 150 passengers at a top speed of 36 knots with a range of 95 nautical miles. Ingouf suggests that 24 metres in length overall with a displacement of around 75 tons is the sweet spot for a foiling monohull powerboat design.“You don’t want to have a boat that has foils sticking out at the sides because you need to get alongside docks and manoeuvre around marinas, and so forth,” he says. “You can certainly go bigger, to as much as 36 metres most likely, but then very rapidly you need a very beamy boat to have the aspect ratio on your foil so you are more efficient at creating lift without adding too much drag. Is foiling the solution to everything? Very likely not, although it’s fantastic in some applications.”<img src="https://photo-assets.superyachttimes.com/photo/308857/image/large-849e3ed467e7f08e313e6c73c4f635a4.jpg" data-gid="gid://syiq/Photo/308857">The future for foils?The future for foils beyond smaller vessels may be limited when it comes to full-flight solutions, but that doesn’t exclude potential for foils in large yacht design. Indeed, appendages that can improve efficiency and comfort – particularly when combined with stabilisation systems to offer multi-axis motion control – have been available for more than a decade. The Hull Vane, a fixed foil or wing designed and patented by <a data-gid="gid://syiq/Company/460" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Van Oossanen Naval Architects (Company)">Van Oossanen Naval Architects</a> that was first fitted on the 42.4-metre <a data-gid="gid://syiq/Company/54" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Heesen Yachts (Company)">Heesen</a> yacht <a data-gid="gid://syiq/Yacht/4639" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Ares42.4m (139'1&quot;)Heesen Yachts2014">Alive</a> in 2012, has proven itself on more than 65 yachts as well as commercial and military vessels.“The Hull Vane is derived from a device we developed for the French America’s Cup campaign in 2002,” says Perry van Oossanen, the studio’s Managing Director. “It’s not really intended to make a boat a foiling vessel as it’s designed for displacement hulls; we’ve taken a different approach by taking the vessel as it is and trying to enhance performance where we can.”&nbsp;The effect is less radical, but so is the technology involved. The location of the Hull Vane under the transom is important relative to the centre of gravity and works best if there’s a steep upcoming flow, which means quite steeply angled buttocks to the transom, but it can be retrofitted on any type of displacement hull.“It works well for a Froude number [the resistance of a partially submerged object moving through water] of 0.2 and upwards,” says van Oossanen. “For a 50-metre boat you’re there at five or six knots, and for an 80-metre boat you’re there at around 13 to 14 knots. We’ve installed it on a 100-metre patrol boat, but essentially the bigger the yacht the faster it needs to go to gain maximum benefit of the Hull Vane.”<img src="https://photo-assets.superyachttimes.com/photo/308778/image/large-e6090620180e08c2025c730977695724.jpg" data-gid="gid://syiq/Photo/308778">Hull Vane BV has also developed Foil-Assist, a partial foiling solution mounted amidships on fast planing vessels that applies the same concept to fast hulls and was first used two years ago on a Wajer runabout. It should be noted that both the Foil-Assist and Hull Vane increase not only efficiency but also onboard comfort – an important consideration for any yacht owner. &nbsp;“However, although applications for foils are definitely increasing, there are a lot of owners out there who are not really interested in the foiling stuff,” warns van Oossanen. “They want to have volume, space and luxury and they don’t necessarily want to cruise at 30 knots.”While that may be true, foiling technology is set to grow, particularly as the superyacht industry enters its own energy transition. Even if methanol in reformers for fuel cells or multi-fuel engines becomes the energy carrier of choice, its energy density is considerably lower for a given volume compared to conventional diesel. So while the fuel may be cleaner, yachts will need to burn less of it for a given volume of tankage to avoid losing too much practical range, while adding more tanks means taking volume away from guest areas. In this scenario, non-flight hybrid foiling solutions could find their niche in mainstream yacht production and there may be a place for more extreme solutions for owners who want a more engaged boating experience.&nbsp;“There is potential for hydrofoil-assisted, non-flying boats, but there is no substitute for flying,” says Bieker. “Once you feel the acceleration that occurs when that last bit of hull leaves the water it is hard to stomach partial foiling solutions.”<img src="https://photo-assets.superyachttimes.com/photo/285014/image/large-1afb80631a7886e71900e1011ca9ab77.jpg" data-gid="gid://syiq/Photo/285014">Getting over the humpWhen the <a data-gid="gid://syiq/Company/327" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Baltic Yachts (Company)">Baltic Yachts</a> 111 <a data-gid="gid://syiq/Yacht/10936" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Raven34.0m (111'7&quot;)Baltic Yachts2023">Raven</a> hit the water for sail trials in the summer of 2023, all eyes turned to this sleek, foil-assisted superyacht. As the team gradually edged the yacht towards its performance limits, the yacht started hitting consistent speeds in the high 20-knots range, and the sailing world was abuzz. However, this style of yacht will probably remain an outlier and while great for exhilarating performance on the water, it is not ideal for coastal cruising with the family. The leeward foil is designed to carry up to 60 per cent of the yacht’s displacement at speed, but the engineering that has gone into creating a structure capable of handling the extreme loads has been immense.“The fitting which is bolted to the hull-deck joint of the foil arm is one metre long and made of machined titanium, for example,” says Kenneth Nyfelt, Sales Director at <a data-gid="gid://syiq/Company/327" href="#managed-by-system" rel="noopener noreferrer" target="_blank" title="Baltic Yachts (Company)">Baltic Yachts</a>. “The tolerances on all those fittings are incredible fine; you cannot allow any rattling or any vibration from it because then you are dead.”Even with Canova’s DSS, Henry Hawkins believes it will take time for most owners to gain confidence in the technology: “Look at how long it took us to get carbon rigging and canting keels onto boats; they’re still the unknown, and what people have taken from the racing scene is that the foils are always breaking,” he says. “So there’s a hump to get over, but I think there is a realisation that there is something to be offered by foiling technology, and it’s a question of how long it will take to find its way into the mainstream.”<img src="https://photo-assets.superyachttimes.com/photo/308861/image/large-11b3b0797fa572b289df3d06472924b7.png" data-gid="gid://syiq/Photo/308861">Tender trendsSmaller foiling boats and RIBs, whether using full-flight foils or foil-assist solutions, offer plenty of potential as standalone leisure boats, chase boats or tenders, particularly as alternative drive systems come on stream. Among many pioneers in this field is Gordon van Hardenbroek, an industrial designer and co-founder in 2015 of foiling boat company Edorado.“We started with a basic design premise of taking a planing hull, taking out the combustion engine and putting batteries in,” he says. “There weren’t many people doing it at the time, but we found as soon as you start going fast the range plummets. And I don’t believe that battery tech will improve enough to solve that problem. We realised that adding foils – in our case an active system made possible thanks to advances in sensors and computation – could double our range. Finally we realised that market demand was for retractable foils.”In addition to creating their own 8.35-metre 8S model, Edorado is also planning to release a pre-engineering platform that targets the superyacht sector. “The 8S is very much about flying,” he says. “It’s not about getting you from A to B, but rather the goal is the flying itself.”

Are foiling superyachts feasible?

The latest technology has overcome many of the shortfalls of older systems, but are foiling superyachts feasible?