A look at an emerging foreship geometry
Axe bow hull design the cutting edge
Among the most dramatic looking new yacht concepts to rise from the drawing boards of leading designers are those, steadily growing in number, that feature a vertical prow, possibly even angled sternward from waterline to sheer, and hullsides ever-so-gently broadening from a knifelike leading edge through uniformly svelte contours, then curving to a raked transom, tracing a profile that appears to merge with the water. But it isn’t just about looks; the axe bow design, perhaps the most noticeable expression of a broader Enlarged Ship Concept, also offers great promise in efficiency, ride comfort and high-speed performance offshore.
Story Jerry Stansfield
While virtually all of these new designs are emphatically contemporary inside and out, the hull form calls to mind a number of precedents. Steam-powered Dreadnought-class battleships of the early 20th century offered a similar profile aimed at reducing resistance in order to achieve the tactical advantage of higher speeds than a more conventional flared bow shape would allow. Power cruising purists will fondly recall early 20th-century plumb-bow designs from, among others, the Elco and Lake Union yards; many of these classics still cleave coastal waters, leaving a characteristically miniscule wake as just-perceptible evidence of their passage.
Although largely coincidental, the historical connection adds an intriguing dimension that mixes classic and modern elements to challenge a growing legion of designers as they shape new interpretations of a hull form that began as a purely practical endeavor. Their work owes its inspiration in no small measure to a remarkable level of cooperation among naval architects and engineers throughout the Dutch shipbuilding industry, and in particular the work of Delft’s University of Technology faculty members in the late 1990s and development teams at Damen Shipyards, a commercial and military vessels builder. With the goal of designing a patrol vessel capable of sustained high speed in often difficult North Sea conditions, Damen engineers first collaborated with the Delft University of Technology’s ship hydrodynamics department on what became known as the enlarged ship concept (ESC). In order to attenuate vertical acceleration or pounding in heavy seas, they first elongated narrower forward sections of an existing 115’ hull design, extending LOA by 20 percent. Jaap Gelling, Damen’s product director of high speed and naval craft, reports that the technique produced a surprising 50 percent reduction in vertical G forces, an achievement that allowed rough water operation with little or no loss of speed, and presented a distinct advantage in an environment where pounding can increase resistance to forward motion and scrub off hull speed, which a prudent captain often must reduce yet further in order to prevent passenger discomfort, seasickness or even injury.
Developed beginning in 2003 as a refinement of the ESC, and with the added participation of the U.S. Coast Guard and the Maritime Research Institute Netherlands (MARIN), the axe bow configuration adds to the increased length an exceedingly fine vertical or nearly vertical prow, with gently tapering forward sections shaped to knife through, rather than slam onto, oncoming waves. Although the design originally was intended for high-speed patrol craft, it also caught the attention of the North Sea petroleum industry, a business that requires a fleet of fast, all-weather replenishment and crew vessels serving the region’s drilling platforms, and one that now operates a growing fleet of axe bow vessels year-round.
“The axe bow was developed for one thing only,” Gelling says, “improvement of seakeeping at high speeds, with the specific objective of 100 percent operability on the North Sea, at 50 knots with a 50-meter (164’) patrol boat.” As a welcome side effect, Gelling notes, the design’s slender forebody reduces resistance by 10 to 15 percent in flat water compared to a conventional fast craft. “One of our customers,” says Gelling, “has a Sea Axe FCS 5009 and a conventional aluminum Fast Supplier with exactly the same propulsion configuration. The ships are used in the same way. As an average over one month, the conventional Fast Supplier uses 1,315 gallons per day, and the Sea Axe 1,115 gallons per day, an 18 percent difference.” Further cooperation between Damen and Delft University, and extensive testing in the MARIN test basin and on the North Sea, have led to refinements in bottom contours and appendage form to eliminate broaching or steering problems in following and quartering seas, notwithstanding the hull’s relatively deep draft at the bow. “Handling and course keeping characteristics are superb in all conditions,” notes Lex Keuning, associate professor of ship hydrodynamics at Delft University of Technology. “There is no broaching tendency in stern quartering and following waves with the ships built by Damen according to the path as laid down in our patents.”
While early axe bow vessels—Damen currently uses the term Sea Axe for its designs—have been developed for commercial, security and military applications, more than a few yacht designers have begun adapting the new hull geometry to their projects. At the forefront of this trend, Feadship and partner De Voogt Naval Architects already have completed extensive concept work on their X-Stream and F-Stream designs, and Feadship recently launched the 239’ Predator, whose rounded stem profile keynotes an elegant, vaguely classic profile that accurately reflects the yacht’s 25 knot-plus performance. With its 37’ 11” beam—more comparable to that of many 200-footers—narrowing to a knife-edge bow, Predator’s hull conforms to the underlying principles of the axe bow geometry. Chris van Hooren, design manager at De Voogt, explains that the slender forward sections encourage designers to position accommodations in the widest part of the yacht, near the center of gravity just aft of the hull’s midpoint, an area of minimal motion already reduced by the design’s tendency to pitch less than a conventional hull. “For patrol and supply vessels, safety and workability are the main design drivers,” van Hooren says, “but the Delft enlarged ship and axe bow concept also offers enhanced motion comfort for yachts.”
While the absence of flare at the bow suggests increased spray over the sheer line forward, Professor Keuning reports that “Spray at the highest speeds in calm water so far is no problem with two small spray rails fitted just above the waterline over the foremost two meters of the bow.” Reint Dallinga, senior project manager at MARIN, adds, “We feel that a very narrow bow will generate slightly less spray that will end up on the foredeck. Shallower flare deadrise angles may generate more spray but it is thrown outwards and therefore, at least in head seas, is less of a nuisance in terms of visibility on the bridge.” High topsides well forward, as seen on most axe bow designs to date, also may help attenuate spray above deck level as the bow drives into oncoming seas.
For many, the look may take some getting used to. Others have embraced the idea wholeheartedly. In the axe bow design’s elongated contours, Russian designer Igor Lobanov recognized an opportunity to create a cohesive exterior style. Of his 344’ White Night design, Lobanov says, “Hydrodynamic advantages coupled with our approach to design to produce a more complete form, a blending of hull and superstructure that takes account of both form and function.” Appropriately, White Night presents a feature knuckle extending the length of the hull, sweeping sternward as a counterpoint to the long, unbroken arc of the deckhouse sides and precisely aligned banks of windows.
For Scott Blee, director of Australian firm SABDES Superyacht Development, the axe bow hull was a logical choice for an ecologically friendly, efficiently driven 164’ concept yacht capable of comfortable ocean crossings and producing, in the manner of those svelte Elco types, a low wake profile, which, he says, “keeps shoreline erosion at a minimum when cruising in environmentally sensitive regions.”
Citing a De Voogt paper that describes the Feadship X-Stream project, van Hooren summarizes the axe bow advantages to include speed (easily over 20 knots), reliability (capable of sustained operation in the maximum speed range), efficiency (lower fuel consumption from reduced wave resistance) and comfort (from reduced vertical motion). Others will add their own favorite attributes, but these alone already have earned the design a close look by casual observers and serious yacht buyers alike.
