Finding more speed and efficiency with fewer trade-offs
May 2, 2014
Stepped-Hull Center Consoles
(Be sure to click through all the images above to read the entire column.) By design, stepped-hull fishing boats should run faster and with better fuel-efficiency than standard V-hull boats — hence their warm welcome from offshore-tournament anglers. However, in the initial years of stepped-hull production, poorly designed steps raised red flags for handling and lower-speed performance. For a better perspective on today’s models and the benefits and challenges of steps, I asked six well-known boatbuilders to explain their outlook on design and function. I focused on larger vessels, although some companies now make bay boats with steps. I asked them three questions: 1) What are the virtues or highlights of a stepped-hull design? 2) What are the trade-offs? 3) What makes your stepped-hull design unique and perform optimally? When shopping for a stepped-hull boat, sea-trial several and make sure all your questions are answered. (Boats are listed in alphabetical order by manufacturer name.) (This material was published in the Fishing Machines column, May 2014.)
Standard V-hulls operate on a triangular running surface, while a stepped hull operates on multiple, triangular running surfaces, depending on the number of steps, says Scott Deal, Maverick Boat Company president. (Maverick builds the Cobia brand. The Cobia 344CC, pictured, the brand’s first stepped hull, was introduced in February at the Miami International Boat Show.) The sum of the area of those triangles — the portion that’s wet when running — amounts to less than that of a single running surface. “This effect increases with speed due to the air-induction action of the step itself, where the outboard portion of the hull, aft of the step, is essentially dry while underway,” Deal says. “The benefit of this is less wetted surface, which equates to less drag and greater efficiency overall, as well as increased top end, of course.”
Stepped-hull design is not new. PBY seaplanes in World War II had them on their hulls, reveals Deal, who is also a pilot. “Unfortunately, some early-generation, stepped boat hulls were not properly designed and would swap ends, something that’s quite dangerous. And that gave stepped hulls a reputation for being unstable,” he says. Cobia has incorporated steps in its 344CC hull (Maverick builds three stepped hulls among its brands) that are not quite as deep as some others currently on the market. Superdeep steps perform admirably at high speed but tend to struggle a bit at the lower speeds that are sometimes required by sea conditions, Deal says. “We believe ours is a perfect balance between top-end performance, safety, and superior ride and handling throughout the operating envelope.”
Contender 39 ST
Stepped hulls increase speed and fuel efficiency by very slightly lifting the running surface of the vessel, and therefore reducing drag, says Les Stewart Jr., marketing director for Contender Boats, which makes several stepped models. Possible trade-offs depend on the hull design itself and vary among manufacturers. “Some manufacturers use a padded rear section, meaning that the deadrise declines the farther back toward the transom you go, creating an almost flat surface in the rear of the boat,” Stewart says. That can make the boat’s ride more jarring. “We maintain our deadrise of 24.5 degrees from bow to stern,” he says. Another difference among step designs lies in the size of the steps and their distance apart. Too large a step can make a boat chine-walk (oscillate from side to side) at high speed, due to too much air being introduced to the hull, Stewart says. If steps are too small, the design does little to increase speed and fuel efficiency. “We feel as though we have found a sweet spot. Our stepped hulls see an increase of 18 percent in fuel efficiency and 10 percent in overall performance compared with their sister deep-V models,” he says. The chine lines, strake positioning, and keel also affect how the boat rides and handles. Some stepped hulls slip out during hard turns. “With our hard keel line and deep deadrise, our hulls don’t experience slippage during hard turns. Our reverse-radius chine and well-placed lifting strakes allow the boat to handle big seas with confidence while staying dry, as well as track true.”
Invincible builds all of its models using a patented design by naval architect Michael Peters, called the Stepped-Vee Ventilated Tunnel. Peters patented his first stepped-hull design in 1982. “The SVVT feeds air under the hull at specified areas for an optimum, all-around better ride,” says an Invincible spokesman. Invincible’s models also carry more than 900 hours of testing. Its 42-foot center-console has achieved a documented speed of more than 68 mph with a normal load and triple 350 hp outboards. The SVVT features a catamaran-like tunnel aft of the steps, which was derived from offshore racing, according to Peters’ design firm. It decreases frictional resistance and increases the lift under the aft portion of the hull, stabilizing the vessel.
Invincible Stepped Hull
The company goes on to point out that controlled tests show the design does not suffer sensitivity to overloading or changes in trim. The tunnel section also reduces the chance of losing control in a turn. In a profile of the 36 Open Fisherman in July 2013, SF’s Jim Hendricks wrote: “The hull also rides remarkably flat. During acceleration from a standing start, there’s virtually no bow rise, offering excellent forward visibility at any speed.”
Scout 350 LXF
While a step design increases lift and creates aeration, which reduces friction, it also allows the hull bottom to vent out the side of the boat, says Scout, which builds the 350 LXF (pictured) with its Dual Stepped-Hull Technology. Scout says its design achieves a 10 to 15 percent performance increase over conventional hulls with similar deadrise. The company also points out that this effectively means less required horsepower. If not designed correctly, though, a stepped hull can suck down into the water or create stability issues, Scout says. “What makes our stepped-hull design unique and perform optimally? Testing, testing, testing,” says Mark Jerkins, a Scout spokesman. “We have had several marine architects, engineers, designers, high-performance race-boat captains, and consultants come here to the facility to assist our own in-house design team headed up by Steve Potts and his son Stevie (our owners) to aid us in perfecting our stepped hulls. Every company attempting to design a stepped hull will experience some trials and tribulations in designing this — we just didn’t quit until it was perfect.”
SeaVee Z Series
SeaVee introduced its new Z Series late last year, and it now makes 32-, 34- and 39-footers (pictured). While not the first to the party, SeaVee says it has performed extensive testing to develop a stepped hull with premier speed and handling characteristics. With a stepped hull, “less hull contacting the water and air-tunnel obstruction can produce instabilities, including lateral oscillation and hooking,” says SeaVee marketing director John Caballero. Some stepped hulls also “struggle to plane unless throttled up to a sometimes higher-than-desirable speed.” With its three-point lifting surface, SeaVee says its Z naturally runs with maximum lift and minimum forward resistance to deliver planing performance at speeds as low as 18 mph. The patented design ventilates the hull through an augmented, four-port air-induction system that maintains air-supply integrity while underway. “This ensures efficiency while eliminating ride instability due to changing hydrodynamic cycles,” Caballero says.
SeaVee Z Steps
Hull ventilation can also disrupt transducer and livewell-intake -performance. “The Z’s specially designed keel pad remains wet while underway,” Caballero says, “which allows for the proper performance of the transducer so that bottom/fish detection is possible at speed. The keel pad also provides the ideal environment for the flush-mounted water feed to the livewell(s).” And finally, the SpeedRails incorporated into the step design ensure that the boat continues to track true through hard turns and maneuvers by producing a counteracting force. This produces an exhilarating ride, Caballero says, while safeguarding the boat’s occupants.
Stepped-hull design came naturally to **Yellowfin Yachts’ **owner Wylie Nagler, who has a background in powerboat racing and tournament fishing. “There are basically two types of drag — water drag and wave drag,” Nagler says. “One, you can do something about, and the other, not so much.” Introducing air through the steps at the bottom of the boat reduces friction between the hull and the water, reducing water drag, he says. “Wave drag is when the boat hits a wave and it slows down. Steps really do not help at all in this situation.”
Yellowfin 42 Steps
Designed correctly, a stepped-hull boat should have no trade-offs, he says. “Yellowfin has chosen to work with much-shallower steps than most in the industry. We feel that it does not take a lot of air to reduce water drag,” Nagler says. Boats with bigger steps inherently run out of shape at higher speeds when the water gets rough, making them difficult to handle. “The key is to make the boat handle and perform at all ranges of speed from high-speed trolling to cruise to wide-open throttle. If the boat performs in all of these ranges, then you will have a successful design.”