On Water Test results
The following data was collected in a 42’ Fountain Lightning with HP700SCi engines, SSMVI drives with 6-blade Hering propellers and without a DriveGuardian installed. A video of the run can be found at http://youtu.be/7s2NbrbGc6E
The boat was fitted with a number of sensors and a Data Logger to collect and store the information. Once back on shore the data was downloaded to a laptop for analysis. The parameters collected during the test run included:
 Throttle Position – This information was used to measure the reaction time of the operator and determine the exact amount of throttle applied during each Synchronization Event.
 Vertical Acceleration - An accelerometer was used to determine exactly when the boat began to leave the water after hitting a wave and the force experienced re-entering the water.
 RPM – The crankshaft speed was captured to determine the peak RPMs when the propeller was out of the water and how far they dropped when it was re-submerged.
 Boat Speed – A GPS sensor was used to determine the exact speed the boat was traveling during the run.
 Torque & HP - A Strain Gauge was fitted to the port engine’s driveshaft that accurately measures the output of the engine and the torque spikes generated by the propeller. This technology is extremely accurate and similar to what is being used in Formula 1, NASCAR, & NHRA. Once downloaded to a laptop, the engine’s horsepower can be calculated using SAE J1349 JUN90 to correct for atmospheric conditions. Essentially this device functions as an onboard dynamometer with a data logger to collect the information for analysis.

Test Data – (no DriveGuardian)
This test was conducted in 1’-3’ waves (per the NOAA near shore forecast) on Lake Michigan, with Northwest winds at 10-15 knots. The purpose was to confirm the existence of torque spikes and to measure the peaks and durations of the Synchronization Events.
Figure 3: Three Second Snapshot Shaft Dyno Data
At a test boat speed of approximately 65MPH, two torque peaks (yellow plot line) are visible in the Shaft Dyno output in Figure 3. Both of the spikes in Figure 3 are 60% more than the engine’s peak output and beyond the stern drives maximum input rating of 1,160 ft-lbs. it is interesting that the throttle position (blue plot line) at the peak of the torque-spike had very little effect on the severity of the spike. This makes sense if you recognize that the torque-spikes are a direct result of having a large mass (engine, flywheel, coupler, drive shaft, U-joints, gear sets, etc.) rotating at high RPM (red plot line) and then being suddenly slowed down by the propeller.

In the highlighted area of Figure 4, a drop of 193 RPM, (red plot line) resulted in the torque jumping from 263 ftlbs
(propeller nearly out of the water) to a spike of 1,278 ft-lbs (yellow plot line) in 0.08 seconds. In this example
the event duration is so short that the operator was unable to compensate and the throttle position remained
essentially constant at 55% open (blue plot line).

Table 1 is the results of a mathematical model of the 1,278 ft-lb torque spike that is highlighted in Figure 4.
Based on the1.52:1 gear ratio for the drive, you can see that the propeller shaft sustained an even greater
torque spike of 1,918 ft-lbs.

In the highlighted area in Figure 5, a drop of 863 RPM (red plot line) resulted in the torque (yellow plot line)
jumping from 103 ft-lbs (propeller out of the water) to a spike of 1,262 ft-lbs in 0.129 seconds. Operator
reaction time was relatively good with the throttle position (blue plot line) dropping just before the propeller
left the water and then increasing to 44% less than a 1/10th of a second before torque spike.
As a great example of rotational inertia, please notice that immediately following the highlighted torque spike in
Figure 5, the throttle position was held at 10% for more than 2/10ths of a second. At this point the propeller is
in the water and the torque spike is gradually dissipating, but the RPMs barely change for a full the full 2/10ths
of a second, even with the throttle practically closed.

Test Data – With DriveGuardian
DriveGuardian was installed in the same boat as in the previous test (42’ Fountain) and run on Lake Michigan in
a NOAA recorded wave height of 1’ with a southeast wind of 5-10 knots.

In the highlighted area of Figure 6, a drop of 621 RPM (red plot line) resulted in the torque jumping from 155 ftlbs
(propeller nearly out of the water) to a DriveGuardian regulated spike of 1,130 ft-lbs (yellow plot line) in
0.095 seconds. Boat speed was 85MPH and the throttle remained approximately 85% open (blue plot line). So,
with an RPM drop of more than 3X the highlighted area of Figure 4 and over roughly the same period of time,
the torque spike was still 12% lower. This plot clearly indicates how effective DriveGuardian is at regulating
torque spikes

Using the same mathematical model as the previous test and based on the data from the DriveGuardian test,
Table 3 shows that it would require an Inertia-Induced Torque of 3,316 ft-lbs to decelerate the rotating mass of
the engine from 5,408 RPM to 4,787RPM in .095 seconds. While some of this energy would have been
dissipated by the propeller, clearly the data proves that DriveGuardian regulated the torque spike to a preset
value of 1,130 ft-lbs and protected the stern drive from a damaging torque spike.