Injury Analysis of Impacts between a Cage-Type Propeller Guard and a Submerged Head
Dr. William R. “Mike” Scott, Dr. John L. Labra, Mr. Herb M. Guzman, Dr. James V. Benedict, Dr. Harry L. Smith, Dr. James Ziegler
SAFE J. 1994 Oct; 24(3):12-28.
Propeller guards have been proposed for use on recreational and military boats. While the guards may prevent body contact with the spinning propeller, the potential of blunt trauma injury may become increasingly significant as impact speeds increase. In order to investigate the potential for blunt injury to the head in impacts between a propeller guard and a submerged head, a computer model of underwater impacts was developed and a series of underwater impact tests were performed. The computer model represents the human body as a multiple degree of freedom system. The physics of impacts in the underwater environment were mathematically modeled and underwater impacts between the head and a propeller guard were simulated with the computer model. In the impact tests series a Hybrid III anthropometric test device (ATD) was submerged in the head up position. A 115 HP outboard motor, equipped with a cage-type propeller guard, impacted the head of the ATD at speeds of 2.5 to 15.7 mph. Head accelerations and upper neck forces were measured. High speed film data were collected. Simulated and actual propeller guard impacts with the ATD head indicate that cervical spine damage and/or focal skull penetration may occur for impact speeds in excess of 10 mph. Head impacts with the side of the guard at speeds greater than 15 mph have a high probability of producing a concussion. The findings suggest that while the use of a propeller guard may be beneficial for low speed head impacts, the problem of blunt trauma injury at speeds greater than 10 mph would make the propeller guard counter-productive in reducing injuries.
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