806 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 76.28 



MENA, Aug 1954, pp. 288-290. These vessels 

 have a single screw driven by a 7,000-horse electric 

 motor turning at 150 rpm. 



LoA = 425 ft B = 61.58 it H = 27.63 ft 

 Lpp = 387 ft D = 36.79 ft Deadweight capacity 

 at this draft = 6,500 tons. 7 = 15 kt. These 

 vessels have a profile resembling almost exactly 

 that of a regular icebreaker. 



(48) "Ingalls Launches Most Powerful Icebreaker," Mar. 



Eng'g., Oct 1954, p. 58 



(49) "The Twin-Screw Diesel-Electric Ship General San 



Martin; an Ice-breaking, Research and Supply 

 Vessel for the Argentine," SBMEB, Feb 1955, pp. 

 108-109; also The Motor Ship, London, Jan 1955, 

 p. 432, and MENA, Dec 1954, pp. 480-481. The 

 last reference contains photographs of the bow and 

 stern of the vessel in the building dock and a 

 photograph of the completed ship under way. 



(50) "Diesel-Engined Soviet Icebreakers," The Motor 



Ship, London, Feb 1955, p. 503. Illustrates and 

 describes the three vessels of the Kapetan Belousov 

 class, as well as the two 12,840-t icebreakers now 

 on order (1955). Abstracted, with outboard profile, 

 in IME, Jun 1955, Vol. LXVII, pp. 86-87; see 

 also SBSR, 6 Sep 1956, pp. 313-315. 



(51) "Icebreaker with 12,000-B.H.P. Machinery," The 



Motor Ship, London, Dec 1956, p. 362 



Lo A ,273 ft 

 LwL , 260 ft 

 Bex , 63.75 ft 



H, mean 22.33 ft 



A, 4,950 t 



Pb (normal), 10,500 horses. 



76.28 Hydrodynamic Design Features of 

 Amphibians. It may be expected that the future 

 will find more and more peacetime uses for a 

 good combination of water craft and land vehicle, 

 notwithstanding that its development to date is 

 due largely to its wartime usefulness. Indeed, the 

 first successful "alhgator" of Donald Roebhng 

 was used originally in 1933, in the otherwise 

 impenetrable expanse of the Florida Everglades, 

 for rescuing hurricane victims and downed 

 aviators. During the recent war its descendants 

 served as means of carrying medical supphes and 

 even as mobile hospitals. Refitted World War II 

 DUKW's are already serving as combination 

 fireboats, rescue, and salvage craft, equally useful 

 on dry land and in the water [Rudder, Aug 1952, 

 pp. 24-25]. There is no reason why they should 

 not be useful as ship-to-shore package and per- 

 sonnel carriers in out-of-the-way places where 

 ships must anchor off and where there are no 

 shore facilities. 



For these duties an amphibian must: 



(a) Run in and on any kind of Hquid or sohd 

 medium, from fresh and salt water to dry land, 

 or any combination of these two. There is no 



permissible "holiday" for travel in mud. If it is 

 soft enough it acts as a hquid; if hard enough, as 

 a sohd. 



(b) Have an adequate reserve-buoyancy ratio, 

 not only for wavegoing but for the bank require- 

 ment of (f) following. This is more important in 

 an amphibian than in a surface vessel because the 

 former can rarely be ship-shaped or have much 

 of a weather deck. 



(c) Maintain the reserve-buoyancy ratio through- 

 out the design and construction period. This 

 means that the total scale weight can not exceed 

 the weight of the hghtest water displaced by the 

 buoyant volume up to the safe working waterhne. 

 Judging by some bitter experiences of the past, 

 it means that an ample weight margin must be 

 included in the preliminary design. 



(d) Possess adequate freeboard to guard against 

 water from the crests of its Velox waves. With a 

 blunt bow and full form, these crests may be high. 



(e) Limit its water speed to 1/3, 1/4, or possibly a 

 smaller ratio of its maximum land speed 



(f) Be able to drop down or run up a bank having 

 a slope of at least 30 deg with the horizontal, 

 both below and above the water surface. 



An amphibian, in the form of a wheeled or 

 tracked vehicle which can propel itself along the 

 surface of the water, or of a boat which can run 

 on dry land with wheels, tracks, or the equivalent, 

 can hardly be expected to have a high degree of 

 propulsive efficiency when running in either 

 medium. If the primary object of the design is to 

 produce a load- or passenger-carrymg vehicle, a 

 watertight body to give it flotation may be a 

 clumsy encumbrance. Shaping this body to ease 

 the water flow around it and at the same time 

 to incorporate a pair of paddletracks, one or 

 more screAV propellers, or a paddlewheel involves 

 compromises Avhich must be worked out for each 

 particular case. Applying wheels or tracks to an 

 object designed primarily as a water craft is no 

 less of a special problem. Fig. 76. T shows how 

 clumsy such a craft can look and still perform 

 well as an amphibian. 



This is not the place to advance arguments for 

 or against the use of wheels or tracks for travehng 

 on land, through sand and mud, or over sub- 

 merged reefs. There might be some reason for 

 discussing the relative merits of propellers and 

 paddletracks if the form of the craft were in any 

 way standardized. It may, nevertheless, not be 

 amiss to list briefly the advantages, disadvantages, 

 and precautions to be observed in adapting and 



