Effect of Shock Absorbing Sheat in High Speed Patrol Craft

Abstract

In order to protect crew against a large accerelation caused by sailing in the rough waves, high-speed patrol ships have been equipped with shock-absorbing seats (seat damper), now. Although the seat damper is popular among the crew, there are some reports of doubtful whether the seat damper is effective to reduce the shock or not.
The author investigated the shock-absorbing effect of the seat damper with a vibration testing machine and the accerelation measurement onboard ship.
The present investigations are as follows. The natural frequency of the seat damper is about 1.8 Hz when a person is seatted on it, and it is considered theoretically that the damper has no shock-absorbing effect unless the frequencies of the impact accerelation are higher than 4 Hz. Both the present results with the vibration testing machine and the data onboard ship endorses also the vibration isolation theory.
When the patrol ship runs in full speed, the main spectrum of the accerelation caused by the sea waves is about 0.3Hz, and no shock-absorbing effect of the seat damper is obserbed in these frequency region. However, in the higher frequencies up to several decade Hertz, considerable vibration reduction is recogniged by using the seat damper.