Haselton 



The closest attention to these elements is mandatory, for the entire system 

 performance is limited by the weakest link. Sensory information is not limited 

 to vision alone, but embraces acoustic as well as position and rate data and may 

 include feel in the form of feelback controls. The sensed information must be 

 displayed to the operator in meaningful formats and utilized effectively as inputs 

 to control systems. If this task is done well, the operator will know what is 

 happening and what needs to happen. The next concern is to permit the man to 

 impose his will upon the machine through manipulation of controls, Thest must 

 be meaningful controls embodying the best practices of good human factors ex- 

 perience. The allocation of all dynamic control tasks to a single operator is 

 mandatory. Last and most important, at least to hydrodynamicists, is the 

 method of generating and controlling reaction forces in the water medium. It is 

 to this element that the bulk of this paper is devoted. 



The generally accepted criteria of excellence for propulsive devices is 

 propulsion efficiency. The history of submersibles leads one ever upward in 

 the quest for higher speed. Maneuvering capability has been solely for the high- 

 speed region with little or no willingness to sacrifice higher speeds for low- 

 speed maneuverability. When one considers the military requirements of sub- 

 marines, it is clear that this emphasis is correct. There has been little interest 

 in performing such tasks as rendezvousing submerged or bottom contour follow- 

 ing at slow speeds for oceanographic or search missions except the recent 

 Palomares effort. 



Recent years have seen a growing interest in the general field of ocean en- 

 gineering, generating a need for maneuvering capability in the zero and near 

 zero speed range. Costeau's Saucer Vehicle is, of course, the best known ex- 

 ample of this new breed of craft. Other later examples are the Alvin, a craft 

 for oceanographic research, constructed for the U.S. Navy, and several com- 

 mercial vehicles which may be typified by the Deepstar, Deepquest, and Alumi- 

 naut. In each of these vehicles, the best-known proven state-of-the-art propul- 

 sion and control schemes were used. 



For the task now at hand, the U.S. Navy carried out an exhaustive search of 

 maneuvering and control devices conducting many tests on those thought to be 

 the most promising, which could perform within the constraints enumerated 

 earlier. The two surviving schemes (Figs. 1 and 2) are generally referred to 

 as the ducted thruster with ring tail and the tandem propeller. The first needs 

 little or no explanation to this audience, being a combination of the well-known 

 bow thruster principle and steerable shroud. The tandem propeller is, perhaps, 

 a new concept to many of you, but is an extension of principles presented four 

 years ago at this symposium. 



The departures from this design are the result of redirection of the per- 

 formance emphasis from high speed to low speed. The two principal changes 

 are (a) the tilting of the blade axis, resulting in swept conical surfaces, and (b) 

 increase in blade area. The first change permits the direction of the large lift 

 forces in the cross body axis without greatly reducing axial capability. The 

 large blade areas provide better force-to-power ratios by moving greater mass 

 through smaller accelerations and at lower rotational speeds. It is apparent 

 that very large force-to-power ratios are possible if blade size or thruster duct 



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