How Variable Rudder Control Was Installed in Slo-Mo-Shun [1950]

Ted Jones, designer, and Anchor Jensen, builder of Seattle Chrysler dealer Stanley S. Sayres' Slo-Mo-Shun IV, solved one requirement—that of variable rudder control—in a simple fashion, working with Western Gear Works.

The design had to provide for:

  1. High ratio control for maximum steering stability at extreme high speed on the straightaway runs during which the boat set the world's record of 160 miles per hour with Sayres driving.
  2. Low ratio control for fast steering on the hairpin turns of the Gold Cup race which Slo-Mo-Shun IV won.
  3. Intermediate control ratios for other conditions.

The solution worked out was to use a standard Michigan Tool Company Cone-Drive double enveloping gear speed reducer mounted outboard at the stern. As shown in the accompanying sketch the pinion in the reducer is linked to the steering column through a 10-foot long tubular shaft drive with two universal joints and a set of one-to-one ratio bevel gears, while the gear shaft is inserted directly into one of the splined rudder posts.

With this design, it was possible to:

  1. Change the reduction ratio to the rudder at will, simply by interchanging standard Cone-Drive gear sets of the same center distance but having different ratios within the reducer housing.
  2. Simplify the shifting of rudder location, since everything is outboard.
  3. Enable the optional use of either one or two rudders (pitman arms connected by a link are mounted on the rudder posts.)
  4. Eliminate practically all backlash and lost motion with a solid drive from wheel to rudder (no pulleys or cables).
  5. Reduce the weight of the drive since a Cone-Drive reducer of only 2-inch center distance was found capable of handling the tremendous torque loads imposed on the 4400pound boat's rudder shaft by the Gold Cup race turns. (The double enveloping characteristics of ConeDrive gears give these gears a much higher torque load capacity than conventional right angle drive gears.)

With this setup, a 10-to-1 ratio gear set was used in the Cone-Drive reducer to control the rudder while the boat was setting the world's record of 160.3 mph.

For the Gold Cup race, a 5-to-1 reduction gear set was used, the speed reducer gears being simply interchanged to provide the different ratio.

Included in the steering setups used with this drive to date on the Slo-Mo-Shun IV are:

  1. A single rudder directly behind the screw.
  2. Two rudders linked together and placed on either side of the screw.
  3. A single starboard rudder 12 inches to the right of centerline, used to set the world's record in Seattle, Washington, recently, and
  4. A single rudder 7 inches to the right of centerline, used to win the Gold Cup race in Detroit, July 22.

(Reprinted from Pacific Motor Boat, November 1950, p.45)

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