Stealth 540By Ben Ellison
t’s not surprising that the waters just outside Miami right after a boat show are chockablock with gorgeous high-performance yachts doing wide-open-throttle, loop-d-loop demos, photo shoots, or just blasting off for home. And what better place to experience the Stealth 540’s oh-so-surprising top end? Time after time—it’s addictive—we slipped this 54-foot luxury cruiser into a slipstream, pinned the twin Bosch electronic controls, waited a moment while the five-blade, surface-piercing props wound up (a good chance to glance aft as the twin roostertails climbed some 35 feet), then felt her narrow hulls gently rise a couple of feet out of the water as her speed got up around 20 mph, then 30, then 40...right up to 50 mph plus, by which time we’d be over the wake and grinning our “bye-bye” condolences.
Actually, though, the most surprising aspect of testing the Stealth was what I didn’t feel: the normally jarring consequences of wake jumping at anything close to that speed. Power catamarans in general do well nosing into short, steep seas, but the Hydrofoil Supported Catamaran (HYSUCAT) foil system incorporated into this hull raises that quality to another level. HYSUCAT should not be confused with those crazy ferries that ride entirely on several strange appendages sticking down below their hulls; the potentially abrupt transitions on and off those foils explain why those designs are almost invariably driven by professionals.
HYSUCAT is a much softer, not to mention better-protected, concept consisting mainly of a single flat wing that joins the two hulls at about keel level and amidships. There are also two fixed winglets aft, but their main purpose is to help get the cat up onto plane (which isn’t quite the right expression for what happens, but what is? Onto wing? Into flight?). If the whole design is working right, and our 540 certainly was, the winglets end up skipping through the scud while the wing stays about a foot deep. Numerous benefits ensue.
First of all, there is even less hull surface to drag through the water, and lesser bows to bash through waves, than a normal catamaran, an advantage I understood when I initially saw the intriguing Stealth in build during a marine press tour of Cape Town, South Africa, last fall. What I didn’t get was how the wing holds the boat not only up, but also down, with the winglets helping to maintain the horizontal angle of attack. When the bows do come out the water, the added weight causes the foil to sink. In other words HYSUCAT includes a vertically stabilizing feedback mechanism, which is why you can hit a wave at speed and only experience an uncanny little bump, as opposed to a bang.
There’s more. The two feet or so of added freeboard the Stealth gets when flying on the foil puts it that much further above a serious catamaran drawback: that throttle-way-back moment when seas are big enough to slam into the center section. Other benefits include a remarkably friendly wake at most every speed—the roostertails are mostly air—plus the almost-flat running angle documented in our test table. Additionally the highly asymmetrical hulls that HYSUCAT uses to shape the water as it passes over the wing and into the big props also take care of another power cat issue: the tendency of some to heel outboard in a high-speed turn instead of into it. (My 14-foot catamaran Gizmo does this, and it feels so wrong, which is why I have learned to lean into turns like a motorcycle rider.)
My Stealth 540 not only cornered normally, her wing seemed to help those turns feel like carving through perfect snow. In fact, driving off Miami in light chop but through a lot of random wake slop was so smooth and fun that everyone tended to forsake the opulent Opacmare bucket seating in favor of a standing head-in-the-wind mode, which led to a phenomenon I’ve dubbed Stealth Hair. The boat also did quite well off plane/wing, once I got used to the fact that engaging the gears produces a hang-on-and-brace-your-feet jerk. Maneuvering around docks, you can either use all that torque plus the unusually widely spaced props to steer with the controls, or switch to the trolling valves for a much lighter touch. The head-in-the-wind handling mode provided excellent sightlines, at least for more common starboard-to landings.
While the HYSUCAT system has been around for many years and looks rather simple, successfully integrating it into a yacht is not. Talking with Stealth managing director and designer Dick Churley, I was impressed with how many factors he had to carefully juggle—like propulsion-system characteristics, weights and balances, and the between-the-hulls cavity shape, to name just the fundamentals. Notice how HYSUCAT seems to limit this 54-foot catamaran to a beam of only 17'11" feet. Yes, that makes finding a slip for the Stealth easier than for most power cats and is arguably the underlying reason why she looks better than most of her breed. But it’s also the source of the boat’s biggest issue, interior volume.
Imagine a wide monohull with a large tunnel up the middle, and you’ll understand the challenge faced by Churley who, incidentally, is an engineering legend around Cape Town. Then gander at the main-deck plan and photos to better understand some of the clever solutions he and his team came up with, like how the raised saloon helm area—a helmsman’s head is nearly at flying-bridge knee level—allows for twin guest heads a level down. While this design also creates good sightlines from that helm, plus a dramatically vertical and top-lit clerestory effect at that end of the saloon, it does somewhat divide that space socially from the galley/seating area farther aft. And that aft area already felt a bit choked, even though an optional coffee table was not installed. This constriction, right at the center of foot traffic, is why, along with the added ventilation it imparts, the unusual on-center windshield door makes sense.
Space issues also led to some systems that many will find desirable anyway. Like, where’s the typical wall of circuit breakers, not to mention bilge and battery monitoring systems, etc.? Instead there’s the far more powerful but compact touchscreens and hidden boxes of an OctoPlex A.C./D.C. system. Similarly, the Stealth’s little 6-kW genset and (undersize-sounding) 50-amp shore-power feed combined with a high-power inverter/charger and large house battery bank may be all that would fit, but some electrical gurus now consider this an efficient and marina-easy configuration.
All this is not to say that design constraints drove all the interesting gear and material choices I saw aboard the Stealth. I was struck, for instance, with how well the multigray interior mix of nubbly linoleum floors, Corian-like counters, faux leather liners and seating, and high-gloss cherry-veneer cabinet doors all work together, then amazed to learn that they came from different suppliers all over the world. I guess that’s one aspect of working in South Africa, where Italy, New Zealand, and the United States aren’t particularly farther away. I’d seen for myself how energetic the mostly thriving South African boatbuilders are about overcoming obstacles like distance from suppliers and markets, which is another reason that a yacht as ambitious as the Stealth 540 shouldn’t be a complete shocker.
Also unsurprising were all the weight-saving strategies used in the 540. Even normal catamarans are notoriously pound-sensitive, a consequence of using two skinny hulls rather than one wide one—and a winged catamaran is even more so. Hence the cored hulls and paneling—even those elegant cabinet doors are cored. But still, as so often happens with Hull No. 1, the Stealth I tested came in overweight; in fact about 3,000 more than the projected 35,700 pounds.
Yet the boat still hit her ambitious 45-knot (52 mph) speed goal, and mind you, nine adults were aboard, along with a lot gear (for the Stealth’s imminent departure to the BVIs). Just look at the numbers I got. I can’t find comparable speed-horsepower-fuel ratios for any similar-size luxury performance yacht, and I’ve looked in PMY’s extensive online library. As for the ride quality, well naturally my reporting is subjective, but that old boat goat Capt. Bill Pike was also onboard, and he noted, “Very impressive performance...good stability, speed, excellent cornering.”
The Stealth 540 isn’t just an extraordinary yacht, but a ground-breaking—or should I say ocean-slicing—one. And she’s not the only luxury HYSUCAT coming to market. That said, the Stealth contains a number of new or little-used technologies, and her interior spaces are unusual enough that you’ll want to thoroughly check them out. But that’s easy, as the relatively small Stealth is part of Voyager Yachts, which, among other things, runs charter bases and fractional-ownership clubs in several desirable locals. So you can experience a 540 yourself—wake jumping and Stealth Hair included—before any further commitment, tempting as an immediate hull deposit might be.
For more information on Stealth Yachts, including contact information, click here.
The man who developed the Hydrofoil Supported Catamaran (HYSUCAT) design used on the Stealth is K.G.W. Hoppe. Back in the 1980’s he was professor of marine engineering at the University of Stellenbosch outside Cape Town; today Hoppe is at Foil Assisted Ship Technologies. If you read the history presented at its Web site, you just might mutter, “What a long, hard trip it’s been.” As simple as that wing foil above looks, integrating it into a production boat is hard.
Or was. Not only did Hoppe tell me that the 540 has proven herself “one of the most efficient and fastest HYSUCAT yachts built,” but I saw yet another HYSUCAT Hull No. 1 under construction in Cape Town (note the unfinished helm module in the photo above). That boat, the Blubay TenderCat 45, is now here in the States and planning an attempt on the New York-to-Bermuda record this spring. You can be sure we’ll cover that story!—B.E.
This article originally appeared in the May 2007 issue of Power & Motoryacht magazine.