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practical. After all, how is a yard to check on the tonnage figure you supply them with? I’ve long proposed that dock-age and storage be based on simply 3.5 times beam. For our three example boats (normalized) this would give bill-able dockage lengths as:

I can’t think of any single change in the boating industry t would effectively result in more efficient hulls than this o If enough people realize that increasing fuel economy is critical to the future of boating, perhaps it will happen. In fact, it could happen if the larger industry associations (NMMA, ABYC, ABBRA, NAMS, Boat/US, SAMS, etc.) all agreed together it was in the best interest of the future o boating and collectively worked for this change. BOAT NAME LOA, ft. Beam, ft.

3.5-Beam Dockage Length Iron Kyle (n) 43.42 13.00 45.5 Imagine (n) 51.17 13.17 46.1 Peregrine (n) 51.72 14.88 52.1 Ironheart 67.00 11.00 38.5

Jet Drives and Efficiency

Clients often ask me about the efficiency of jet drives. The short answer is that jets are usually (not always) less efficie than propellers. Remember that the larger the propeller diameter and the slower the RPMs the more efficient the prop sion on displacement to semi-planing boats. Jets by their very nature have limited impeller diameter and limited (smallish) intake and outlet diameters. The fundamental laws of physics mean that—at low to moderate speeds—jets w always be at least somewhat less efficient than a properly sized propeller.

As boat speeds increase, the appendage drag of the propeller, shaft, strut, and rudder—the running gear—increases geo metrically. Albert Hickman (the inventor of the Hickman Sea Sled and of the surface drive) said, “The resistance of wat at 60 knots is the same as the resistance of hard cheese at 3 knots.” He was right. This is why he came up with the sur face drive—to reduce the drag from running gear at high speed.

Jets accomplish this same thing. As speeds approach 25 to 30 knots—even though the actual thrust delivered from the is less than a comparable prop—the reduced appendage drag compensates. From 25 to 30 knots you will loose some e ciency with properly proportioned jets but not too much. As speed increase over 35 knots, the reduction in appendage drag can make jets net out more efficient than props. This holds up to around 60 knots, where the surface drive is gen ally more efficient than jets or standard propellers.

Jets offer other advantages: shallow draft and extreme maneuverability. It can make good sense where these to featur are primary mission goals to go with jets even in the 22- to 28-knot range. The modest loss in efficiency may be worth-while. At higher speed there should be little loss, and at high speed an actual gain.

In recognition of eighty years of training successful boat designers, Yachting magazine has run a fe ture story on Westlawn Institute in its May 2011 issue. Written by Westlawn graduate and Yachting

editor at large, Jay Coyle, the story recounts the history of the school and explores the success of its alumni.

“If you are a boat owner, there’s a good chance that a Westlawn graduate had something to do with your boat’s design. The list of alumni reads like a who’s who of yacht design. Graduates of this home study course have played a major role in shaping the sport, and some very dedicated designers have played an important role in shaping Westlawn . . .”

Clic k HERE to read the full article online.

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