Towed Underwater Vehicle Applications from 1960 through 1975

Abstract The V-FIN towed underwater vehicle was introduced into the oceanographic and marine operations market in 1960, to provide a stable high speed, light weight and efficient means to deploy instrumentation to a depth from a moving vessel. This paper describes various applications of the V-FIN depressor from 1960 to 1975. Each application includes a written description and other support data. In summarizing the various applications, an updated family of performance curves are presented which were generated from tests performed at the Navar Ships Research &Development Center in late 1975. Using these curves and a new computer program for calculating towed systems performance, the predictive capabilities of the computer program are evaluated in terms of accuracy of calculation with confidence limits. With this background and analytical techniques presented in the subject paper, the reader is provided valuable tools for designing towed systems using experience gained over the past 15 years with applications ranging from lifting antennae to the surface from submerged submarines, stabilizing seismic streamer hydrophone arrays, helicopter bathymetric surveys to combined subbottom/side scan surveys at continental shelf depths. Introduction The towed systems described in this paper are made possible by the development of the V-FIN (Vehicle for Instrumentation) and Haired Fairing. The V-FIN towed underwater vehicle utilizes reinforced fiberglass plastics in its construction which allows for repetitive and accurate manufacture of the hydrofoil shape of the vehicle: The key to the success of the VFIN towed underwater vehicle is its integrated shape which eliminates the need for a separate body, wing, horizontal and vertical stabilizer. This integration of functions into one continuous shape provides the all important ruggedness which is needed to survive in applications at sea. A vehicle with a higher Lift/Drag ratio than the V-FIN's which normally runs from 5:1 to 6:1 can be designed but its cost in serial production, its mechanical strength and stability over a broad speed range would not meet typical requirements. Fundamentally, the V-FIN vehicle generates depression force, not by its own dead weight, but by dynamic means due to hydrodynamic flow over its precisely shaped wing surfaces. Typically a V-FIN generates 10 or more times its weight on deck in depression force when it is towed through water at 12.5 knots. Its depression force varies as a square of velocity. Thus, towed systems can be designed which are essentially depth balanced systems where the increased cable drag with increased speed is balanced by a corresponding increase in V-FIN depression. Another component developed by ENDECO/ BRAINCON is Haired Fairing (1 &3). Haired Fairing consists of filaments of urethane rubber attached to the trailing edge of a towed cable using a braided wire jacked. The advantage of this construction is that each filament is individually attached to the cable and can freely adjust to the flow streamlines as the cable angle of attack or rotation is altered.