Concept of using drogue chutes as a ship decelerator system

The aim of this paper is to present the concept of using drogue chutes as a suitable ship decelerator system in cases of emergency. This concept was studied by deploying and towing drogue chutes in various configurations under the required initial conditions. A feasibility trade study, previously completed, had concluded that clusters of drogue chutes were likely to be the most successful at meeting the deceleration requirements and logistical challenges of system staging and deployment. The original idea was to use clusters of chutes, entangled around the bow of the ship and deployed behind the stern of the vessel, to provide sufficient drag forces to reduce the momentum of the vessel. A first set of trials were performed at 1/10th scale to study the basic drag performance of the chutes in water (but near the water surface), possible interferences between chutes, and reduction of drag performance when the chutes are deployed in clusters. A second set of trials were performed at 1/8
^th
scale to observe optimum chute number, trailing distance, and separation distance configurations as well as inflation dynamics of packed drogue parachutes deployed at full speed. The following findings are presented in this paper: the resultant drag coefficients (Cd) of the chutes as towed in various cluster configurations at various separation distances; the effects of the trailing distance on the Cd; and the stability of the chutes in various configurations. The requirements for the decelerator system were to provide the drag force required to decelerate a large vessel travelling >;20 knots to a significantly reduced speed in the shortest time possible in littoral waters of <; 40m-50m depth. A disabled propulsion system is assumed. Two basic chute configurations were studied; (i) having all the chutes positioned in tandem (i.e. in series) on a single tow riser, and (ii) having 2 tow risers, one on each side of the vessel, with chutes in tandem on each line. The study varied the trailing distance behind the stern before the first chute, and the separation distance between the chutes (i.e. canopy to canopy distance).