ABSTRACT The interactions between a semi-submersible drone and its large towfish, where the tension in the tow cable joining them is about 20% of the weight of the drone, are investigated_ Since standard cable dynamics modelling computer programs do not model tow-vehicle/tow-body interactions, an iterative approach to calculating these interactions is developed. Drone motions are modelled with a non-linear, six degree-of-freedom, underwater vehicle simulation incorporating pre-defined, three component, time dependent tow cable tensions applied at the tow point. Cable dynamics are modelled with the nonlinear, finite segment, cable/towfish dynamic simulator DYNTOCABS, which accepts pre-defined tow-point accelerations as time varying boundary conditions. The interactions are calculated by iterating between these two programs. The method is applied to simple turning maneuvers important to minehunting operations.
1. INTRODUCTION DREA and ISER are evaluating issues facing the development of a Canadian Remote Minehunting System (CRMS) for the Canadian Navy. The CRMS is an autonomous, snorkelling drone towing a deployable, active towfish which houses a side scan sonar for route surveying and mine location on the sea floor. With route surveying, sonar images are obtained from an area where mine hunting is anticipated, in order to provide a reference against which future mine hunting images can be compared. A high degree of towfish stability is required to get good images, and the absolute location of the towfish must be known for differencing images with those from subsequent mine hunting surveys. The semi-submersible DOLPHIN (Deep Ocean Logging Platform for Hydrographic Instrumentation and Navigation) Mk1 vehicle developed by ISE Research Ltd. is a proven stable remote platform for hydrographic instrumentation. It can operate in up to sea state 5 and has successfully demonstrated its towing capability (Preston and Shupe, 1993). DOLPHIN Mk2 (Figure 1) is currently a candidate drone for the CRMS.