A High-Speed Towed Planing Vehicle

Abstract

A wave-following towed planing vehicle operates in head seas, Sea State l and 2, at speeds in excess of l 6 knots (824 m/s). The as-built beam of the vehicle is either 4.25 in (10.8 cm) or 7.75 in (19.7 cm), for the two configurations; V-hull (deadrise pointing outboard) or catamaran (deadrise of each hull pointing inboard). Thus the Froude number is in excess of 8.1 or 5.9, respectively. For stable operation the vehicle requires a tail attached to the stem of its deck. The most successful tail tested consists of several feet of cord tied to a materially dense truncated cone or drogue, which provides drag as it plows through the water. The vehicle is apparently always stable in calm seas. In head seas, the stability of the vehicle depends on the cable angle (the angle measured between the freestream flow direction and the tangent to the tow cable) where the cable attaches to the body. The vehicle is apparently always stable at speeds up to 22 knots (11.3 m/s) at cable angles above 0.185 radians (10.6 arc degrees). At smaller cable angles the vehicle is apparently stable up to 16 knots (824 m/s) in head seas. Tow cable tension measurements reveal tension between 180 and 360 N ( 40 and 80 lb), with tension spikes occurring at frequencies approximately equal to the wave encounter frequency. Heave and roll acceleration measurements on the vehicle indicate average acceleration values of approximately 4-6 g's, with spikes up to 12 g's.