BEHAVIOR OF UNUSUAL 

 SHIP FORMS 



E. M. Uram and E. Numata 



Stevens Institute of Technology 



Hoboken, New Jersey 



INTRODUCTION 



Four years ago, almost to the exact date, the Third Naval Hydrodynamics 

 Symposium, constituted and attended by many of the gentlemen participating in 

 this symposium was held at Scheveningen in the Netherlands; a short skip, gur- 

 gle, or flight from here, depending upon which unusual high performance ship 

 one chose to use. Almost the entire symposium was devoted to discussions on 

 the nature and problems associated with high performance ships. The papers 

 of Mr. Owen Oakley [1] of the United States Navy Bureau of Ships, Dr. Van 

 Manen [1] of the Netherlands Ship Model Basin, and Dr. Breslin and Professor 

 Lewis [1] of our own laboratory, at that time pointed out many of the design and 

 operational problems attendent with the unusual ships shown in Fig. 1. Their 

 relative power and seakeeping behavior were discussed based upon reasonable 

 analytical estimates, or very limited experiments. A substantial number of the 

 other papers presented at that symposium and at other subsequent meetings of- 

 fered information concerning the performance and limitations of hydrofoil craft, 

 planing craft, and OEM's. We will not reiterate these arguments at this time, 

 but just point out that the prime objective is the attainment of high speeds in 

 rough seas while maintaining reasonable horsepower requirements and reducing 

 the well known severity of motions in seas at high speeds. 



We will be concerned in this discussion primarily with unusual surface or 

 sub-surface vessels in the 3,000 ton displacement class at speeds in the vicinity 

 of 40 to 50 knots, although we will discuss the behavior of these ships over the 

 entire speed range. The design philosophy of unusual form surface ships such 

 as the Large Bulb Ship (Escort Research Vessel) and the Semi-Submerged Ship 

 (Decks Awash Ship) is such as to change the pitching and heaving periods so that 

 the ship will operate in sub-critical or super-critical zones of operation as de- 

 fined by Professors Lewis [2] and Mandel [3]; operation conditions in which the 

 ship is not in resonance with the encountered wave system. The shallow running 

 submersibles like the Shark Form and Semi-Submarine take advantage of the at- 

 tenuation with depth of wave system effects. However, the single surface pierc- 

 ing strut of these ships makes them unacceptable from a stability and control 

 point of view. The Hydrofoil Semi -Submarine, Fig. 2, is a design conceived by 

 the senior author [4] affording inherent stability in this ship type. The stability 

 referred to is defined as the ability of the vessel with controls fixed to seek and 

 return to its initial trim, depth, and course after being disturbed from these 

 conditions. 



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