Shannon 38 SRD — By George L. Petrie — January 2005

Four in One

The Driving Force

More of this Feature • Part 1: Shannon 38 SRD • Part 2: Shannon 38 SRD • The Driving Force • Shannon 38 SRD Specs • Shannon 38 SRD Deck Plan • Shannon 38 SRD Acceleration Curve • Shannon 38 SRD Photo Gallery
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Walt Schulz is a man on a mission. Convinced of the inherently greater efficiency that surface drives offer (by greatly reducing appendage drag), he is equally committed to the conviction that conventional hull forms are ill-suited to take advantage of those efficiencies. To get the drive train (and half the prop) out of the water, surface-drive systems generally require that some sort of complex apparatus must be mounted on the transom above the waterline, typically extending several feet aft of the stern with an exposed propeller spinning at the far end.

Schulz believes he has a better way, and he’s out to prove it with his third Shannon 38 SRD. Molded into the bottom of the hull, extending forward from the transom, is a cavity about 2'x2' in cross-section and about six feet in the fore and aft dimension. Using conventional shafts, struts, and bearings, the running gear will be mounted within the cavity, with only the lower half of the prop extending below the base of the hull. To assure smooth flow into the prop, the bottom of the cavity will then be sealed with a metal plate (faired into the hull) that terminates a few inches ahead of the prop. This arrangement promises to deliver all the advantages of current surface, drive systems, while eliminating their complexity and related safety issues.

Schulz’s idea is certainly a departure from conventional wisdom. But then, so are the concepts of the Shannon 38 hull form, and they’ve already proven to perform as he intended. There’s a real chance this visionary yacht builder will also revolutionize our thinking about how to design a surface drive. —G.L.P.

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