1Graduate school of fisheries science, Hokkaido University, Hakodate, Hokkaido 041-8611, 2Faculty of fisheries science, Hokkaido University, Hakodate, Hokkaido 041-8611, Japan
This paper describes the characteristics of a towed sampling gear system by using a linearized equation of motion. The linearized model was validated by comparing the results of the simulation and actual operation using the system of R/V Ushio Maru and a FMT (Framed Midwater Trawl). Damping factor and natural frequency, which are two parameters of a second-order system, were expressed as a function of the specifications of the sampling gear and operational conditions. As a result, the motion of the system was regarded as over-damping in common operations, and so the system generally seemed to be approximated by a first-order system. In this approximation, the value of the time constant remained constant even though the virtual mass of the net was varied. It was also found that the advantage of stable towing depth was obtained by using warp with a small scope ratio.