W. C. SCHULTZ ENGINEERING INC.
CHULA VISTA, CA 92010

“PROP GUARD”

PERFORMANCE TEST OF THRUST ENHANCING PROPELLER GUARD
FOR OUTBOARD MOTORS AND STERN DRIVES

ABSTRACT / PERFORMANCE EVALUATION TEST

This report is comprised of tables and photos illustrating the performance of a thrust enhancing propeller guard.

The test procedure was comprised of:

1. Pole test, with and without propeller guard.
2. Speed test with another boat in tow, and with the guard installed, and without the guard.
3. Speed test of the test boat alone, with and without the propeller guard.

The pole test was made July 9, 1998 at the “J” Street Boat Launch Ramp in Chula Vista, California. The tow speed test on July 14, and the speed test with the test boat only on July 17, 1998. Speed tests were made in Chula Vista Marina Channel between Channel Markers Numbers 17 and 21.

The test boat used was an 18 foot Century 190 Deep “V” Hull Runabout, with a 230 hp. OMC Stern Drive, fitted with a 15 x 17 three blade propeller. This boat had six people aboard, weighing approximately 1180 pounds total.

The boat in tow was an 18 foot Deep “V” Hull Runabout, with six people aboard weighing approximately 1125 pounds total.

Measurements were made with and without the propeller guard at each test to obtain the resulting performance data.

The test data indicates outstanding gain in overall boat performance, with the propeller guard installed; such as:

1. Significant greater thrust (towing skiers, etc.).
2. Higher cruising speed at medium motor RPM (with resulting fuel savings; sport fishing, cruising and touring).
3. Significant directional boat steering control.
4. Outstanding boat leveling trim control.
5. Complete propeller protection (water skier safety).
6. Significant reduction of propeller wake (preventing wake nuisance for boats nearby and preventing wake damage to river and channel banks).
7. The vortex vanes between the outer and inner guard nozzle create a similar effect as contra-rotating propeller arrangements, canceling the torque reaction, and the propeller vortex of a single propeller installation (simple application for submarines and torpedoes).

The basic principle of the thrust enhancing propeller guard, and the reason for its high performance is the triple concentric positioned nozzle ring configuration and the vortex vanes between said rings (patent pending). The entrance side of the outer rings is much larger than the propeller, drawing in more water than the open propeller and achieving greater thrust. Because of the acceleration of the water into the nozzle rings, the pressure inside is less, hence a forward thrust is exerted on the nozzle guard and the drive, and from the drive housing to the hull.