Shannon 38 SRDBy George L. Petrie
When I first asked designer/builder Walt Schulz what his motivation was in designing the radically different hull form for the new Shannon 38 SRD, his answer was disarmingly candid: bad knees.
Apparently sensing my perplexed reaction, he launched into a more complete reply. His company, Shannon Yachts, has been building sailboats for some 30 years and powerboats for almost 20 years. His knees, and those of many of his customers, long for a hull that can deliver planing-boat speed but with a softer ride than any existing hard-chine, V-bottom form. Having heard my wife voice the same yearning over the years, my curiosity was instantly aroused.
As Schulz continued his discourse, he conceded that there was also a second, much more profound objective: developing a hull that would be optimally suited for use with surface-drive systems. And not the surface drives that are presently available, which protrude several feet aft of the transom, but a surface drive that can be mounted under the hull and not require any special equipment—just a prop and a shaft, in a suitably designed cavity beneath the hull. Now my curiosity was really piqued.
According to Schulz, the main advantage of a surface drive is that it can reduce appendage drag by nearly 80 percent, because the shaft and struts are up and out of the flow of water beneath the hull, while just the bottom half of the propeller is immersed. Hull No. 3 is presently under construction in a single-screw surface-drive configuration.
The drivetrain installed in our test boat, Hull No. 1, was a conventional twin-screw inboard configuration powered by a pair of 160-hp Yanmar diesels. But I was no less anxious to see how the novel hull form would perform. Her bottom shape was unlike any other fast powerboat I had ever seen.
Schulz describes the hull as a combination of four shapes. The waterline sections in the forward-most four feet of the hull are “hollow” (concave in plan view) to “push aside water at the bow that you don’t want.” The next four to six feet aft are “round” sections (convex in the transverse plane), “similar to the shape of a sailboat hull, to give a soft ride.” (Remember, Schulz has been building sailboats for 30 years.) The midlength has an undulating cross-section, which Schulz refers to as a “vortex generator” that redirects flow upward toward the stern to provide lift and a smooth flow of water into the props. And finally, the aftermost ten feet is a gently cambered section that forms a reverse deadrise, providing the lift necessary to combat stern squat when the boat exceeds her theoretical hull speed of about 8 knots.
They say seeing is believing, and although Schulz has a convincing manner, I wanted to see for myself whether he was really onto something, or if he just had an impressive-sounding sales pitch. What puzzled me most was that the hull had a hard chine only over the last few feet of its length. How could flow separate at the chine (allowing the hull to plane) if there was none, but only a large-radius, round bilge over most of her length?
As I eased the boat out of the harbor into Rhode Island’s Narragansett Bay and pushed the throttles forward, my misgivings were quickly put to rest. The twin Yanmars spooled up, and the readout on my radar gun climbed steadily, topping out at nearly 25 mph. We made a few more runs to check trim readings—I figured my trim gauge had developed a snafu, because the trim angle was pretty much a constant 2.5 degrees over most of the speed range. There was no bow rise at all, and in our path we left virtually no wake. Seemed to me Schulz really was onto something.
As impressive as the hull is in straight-line performance, she really shines in the corners. At full throttle, I yanked the wheel hard over—a standard boat-test maneuver that sometimes elicits startling results. But I’ve never experienced anything like this. The hull banked ever so slightly and seemed to pivot like it was tied to a string, carving a turn with a radius of about two boat lengths. Tight figure-eights were the same—no fuss, just tracking and turning like she had a six-foot centerboard under her keel. And low-speed maneuvering was just as sure-footed, even with her modest two-foot draft.
Though we ventured all the way to the mouth of Narraganset Bay, we found nothing more challenging than swells about two feet high to test her rough-water performance. But from her hull form, I have every reason to believe that the Shannon 38 rides as softly as Schulz claims, although with her round bilge, she does tend to take a bit of water on deck. (Editor’s note: During the Newport Boat Show, I ran the same 38 through some large waves and found her ride quality amazingly smooth—not a hint of pounding on any course.—Richard Thiel)
Though hull form is a big factor, another important element contributing to the boat’s performance is her light weight, due in large part to the PVC foam coring used throughout her hull and decks. Her bow sections are reinforced with Kevlar-glass hybrid reinforcements, so owners can safely indulge the temptation to beach the shallow-draft hull on a sandy shore. And her internal stiffeners are molded separately from the hull, then glued in place with Plexus, an adhesive that yields a stronger joint than the more common “tabbing and secondary bonding” methods.
Shannon is equally fastidious about the quality of joinery, fit, and finish. The varnished mahogany in our test boat’s interior was flawlessly finished, making a nice match with the teak and holly soles throughout the lower deck. To ensure consistency, all woods used in joinery are hand-picked for grain and color. Although Shannon will configure the interior layout of each yacht to suit the owner’s wishes, the proportions of the lower-deck spaces convey a definite “sailboat” aspect, with a narrow but adequate V-berth forward and the galley and head at the base of the companionway. Our test boat had a truly spacious saloon, with two facing settees separated by a beautiful custom cocktail table, but the space is large enough to accommodate an optional second stateroom.
Another feature I liked on our test boat was the custom helm seat, finished in soft Ultrasuede with stainless steel frames and tilt-up arms, and wider in the seat than a standard chair for a bit more wiggle room. A pair of deck hatches offers good access to the engines, while a third hatch in the swim platform affords access to the steering gear and room to stow shore-power cords and dock lines.
It struck me as a bit ironic that the Shannon 38’s relatively conventional cockpit layout belies her radically different shape beneath the waterline. Notwithstanding her distinctive exterior styling, she gives no obvious hint of the profound achievement that her design represents, delivering the speed of a true planing hull and the comfort of a full-displacement hull. I can hardly wait to get onboard Hull No. 3 and wring out the new surface-drive version.
This article originally appeared in the January 2005 issue of Power & Motoryacht magazine.