There are numerous public records of self-actuated transmission accidents for both automobiles and boats. However, record-keeping practices does not identify most of the marine incidents of self-actuated transmissions.
Typically, when a boat operator is prepared to remove a water skier from the water or to pick up a diver, the boat is floating free, slowly drifting with the current and wind, with the engine running but idling in neutral, as the operator.
Suddenly the gear shifted into forward or reverse without any action by the operator. If the person in the water is aft of the propeller and the gearshifts to reverse, the propeller wake (suction) will force the swimmer towards the propeller and major injuries or death will result.
We investigated two similar accidents; one resulting in two deaths and the other had serious injuries.
In one of the accidents investigated, a boat used to transport divers to the diving area, reached the area of diving and the operator put the gear in neutral. Two experience divers were in about 150 feet of water while the diving boat was drifting above them. Suddenly, one diver developed problems with his air supply and signaled his buddy for assistance.
Both started sharing the regulators and air of one of the divers and commenced a quick ascent with their bodies in very close proximity. Probably they were busy trying to solve the air supply problem and did not pay attention to the location of the boat above them as they were ascending to the surface. When they reached the boat, they hit the bottom of the boat or one of the propeller shafts, and the bump caused the gear to shift from neutral to forward. Both divers were killed instantaneously.
A typical marine gear will have a �detent spring roller� that could end up in an unstable position between neutral and forward or neutral and astern and a shock or vibration may cause the detent to shift to the closest indentation in the "detent plate".
Automobile gearboxes used to have similar problems resulting in expontaneous shifting from an apparently parking position to a gear position whenever the manual lever may or may not be in the full park position. Normally a driver assumes that he has completed the shifting task on the basis of selector "feel", while an unstable condition could easily result in the detent spring forcing the transmission into the reverse position.
The gearbox was removed carefully to be inspected. The detent plate appeared to have a slight wear, so the self-actuated marine gearbox was tested in a shop, where after positioning the �detent spring roller� purposely between the indents of the detent plate, it was found that it would shift to gear after a number of shocks of various magnitudes were applied. Replacement of the detent plate and detent roller improved the operation, but does not eliminate the possibility of self-actuation in the future as the detent plate and other components start wearing off.
This accident could have been prevented, since the boat was specifically used to transport divers to the diving site, a propeller guard would have been installed to protect the divers.
In the U.S.C.G. annual list of boating accident statistics, there are about 7 fatalities and 100 injuries attribute to being struck by a propeller. There is no question that a guard surrounding the propeller will mitigate these types of injuries.
Under certain circumstances, a boat with a propeller not having a propeller guard can be considered to be defective.
The following is a sample of the above:
Jeanne Sprietsma was killed in 1995 when she fell off a ski boat and was struck by a Mercury 115-hp outboard propeller. The original lawsuit, filed by her husband in Cook County Circuit court, IL, claimed Mercury�s engine was defective for not have a propeller guard, even though none is required by any state or federal regulation. The Supreme Court ruled unanimously against federal supremacy in this case. Over the years, the Coast Guard has commissioned research and reports on propeller safety and in 1990 decided not to promulgate regulations. Since then, the federal government has confined its interests to propeller hazards on houseboats and non-planing vessels.
Generally, propeller guards fall into one of the five categories below:
For a boat used to transport divers to the diving site, the most appropriate propeller guard would have been a full cage propeller guard.
Hector V. Pazos is a Naval Architect, Marine Engineer and a Registered Mechanical Engineer and has been engaged in Accident Investigation/Reconstruction for more than 35 years. He has been retained as an Expert Witness in over 1,200 Maritime cases, related to both commercial vessels and pleasure crafts, for both defense and plaintiff.
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