Tunnels Can Improve Performance... - 11/28/2007
A boat builder and a designer take issue with Mike Meyer

Frank Piedra started in the marine industry in 1962 with Winner boats, the first company to build fiberglass boats in a production line. Later he was with Sea Bird and was the president of Phoenix Yachts from 1976 to 1999. He now runs a world-wide marine consulting business. Perhaps the most famous, and certainly the most innovative was the Phoenix 29 “pocket convertible” which offered Volvo Penta TM40 diesels as options. He boat he built:

Mike Meyer's discussion of the Volvo IPS was very interesting but I have two comments:

  1. The propeller pockets benefits -- properly designed – not only are shallow draft and have a low engine envelope profile but also improved performance. The work and tests we did in 1974 and 1975 at Sea Bird and later on in the late 70s at Phoenix, under the guidance of Jim Wynne, proved this statement. In one case we tested two identical 29s, same engines, same weight, etc., ran them side by side and even took "movies" of them. Under all conditions the 29 with pockets was faster, had a better running angle, turned sharper and the fuel consumption was identical.
  2. Another thing that may have influenced Volvo to stay away from pockets is the Wollard patent (3,469,557). In the mid 80s Sea Ray, Phoenix and two other companies were sued for infringement. Jim Wynne was very much involved in the litigation. (Jim Wynne is credited by Volvo Penta has the inventor of the stern drive.)

Tunnels Can Improve Performance, Says Blount

Bill Blount is President of Donald L. Blount and Associates, a leading American naval architect firm, which is responsible for some of the fastest large powerboat hulls ever built.

DLBA worked closely with Volvo Penta in the early design work of the IPS pod system, and has designed hulls for the IPS pod drives for a number of builders. Blount reports that tunnels are not necessarily less efficient in powerboat hulls. He says that properly designed, with proper propeller blade tip clearance they can improve performance in certain applications.