Boat Design: A “Maintenance Strake” on the Nordhavn 63

The new Nordhavn 63 features a unique hull feature that adds room around the engine and actually reduces drag. We examine this feature in some photos and learn what the inspiration for it was.
N6301 Hull With Maintenance Strake Highlighted -- Original Photo Courtesy of PAE

N6301 Hull With Maintenance Strake Highlighted -- Original Photo Courtesy of PAE

We ran a story yesterday with some new photos of the Nordhavn 63 debut hull in construction at the factory in China.  As many of our readers know, part of the Nordhavn “mystique” is a result of the reputation of its full-displacement, bluewater hull designs.  These are the products of PAE’s chief designer Jeff Leishman, younger brother of one of the company’s co-founders and design contributors, Jim Leishman.  Over the years, the basic hull designs have been continually refined and have benefited from tank testing and analysis.  If you look closely at one of the photos from yesterday’s article, which I have marked up here with a black oval and arrow, you will see a somewhat unusual appendage on the bottom of the hull where the keel fairs into the flatter line of the hull bottom.  It looks in this angle to be a kind of bulbous addition to the hull.  Being a reporter and not afraid of my own naiveté, I decided to ask PAE’s Dan Streech about it.

“We call those ‘maintenance strakes’,” says Streech.  “They provide the room inside of the boat to walk around the engine.”  It sounds like an interesting way to add depth to the engine room.  Obviously, it would slightly increase the displacement of the hull, but I wondered how they came up with this idea and what the effect is, hydrodynamically speaking that is.  The answer Streech provided sheds a little light on the nearly unlimited sources of imagination and inspiration of the Leishmans.  According to Streech, “Jeff and Jim conceived and invented those while sitting on a turbo-prop plane and noticing all of the bumps, bulges and nacelles which didn’t seem to prevent the plane from flying.”  Streech adds, “We tank-tested them and actually found a reduction in drag (for reasons which were never fully explained).”

Cessna Caravan with Baggage Fairing -- Photo: Wikipedia Common License

Cessna Caravan with Baggage Fairing -- Photo: Wikipedia Common License

In the photo above, you see a Cessna Caravan, a turbo-prop-powered passenger and utility plane which uses a large faired extension on its fuselage (the “hull” of an airplane) to achieve a similar capacity increase.  Given that the aircraft is not designed for speeds higher than a couple of hundred miles per hour (relatively slow in commercial aviation terms) the drag penalty is negligible.  It would probably be somewhat different if the Caravan were intended to fly supersonically, but that’s a different kettle of fish.

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Posted by Tom

Tom Tripp is the owner of OceanLines LLC, the publisher of OceanLines and founder of Marine Science Today. He is an award-winning marine journalist, science writer and long-time public communications specialist. His PR career and much of his writing stems from the fact that he loves to explain stuff. It all began when he and his brother Mark threw all of Mom’s tomatoes at the back wall of the house. . .