LOADS ACTING ON A SHIP AND THE ELASTIC RESPONSE OF A SHIP 



275 



Table 5 Model Ship Characteristics (from Ochi, 1956b) 



Model Ship Characteristics 



The resulting efi'ective \v;i\'e-height ratics are .shown in 

 Figs. 2()(fl) and (b). Oehi's towing-tank data arc in 

 agreement with Sehnadel's sea observations in that the 

 effecti\e wa\e-height ratio is appreciably less than unity 

 even when the Smith effect is taken into account. The 

 speed parameter Fm tlie ca])tion of Fig. 26 is the speed- 

 length ratio, V \/L, with 1' in meters per second and L 

 in meters. 



4.3 M. Safo— Destroyer Model. M. Sato (1!)51) 

 presented an outline of the towing-ttmk experiments con- 

 ducted prior to the end of World War II in 1!)45. The 

 experimental study was initiated in 1935, following the 

 breaking up of two destroyers in a severe typhoon. 

 The major part of the data was lost because of the war 

 damage and subsequent confusion but Sato's paper 

 nevertheless contains much valuable information. 



The body plan and priiu'ipal dimensions of the model 

 are shown in Fig. 27. The model was made of half- 

 hard brass plate. The longitutlinal members (keelson 

 and two deck stringers) were made continuous as far as 

 possible and the transver.se members were intercostal 

 and riveted. The frame spacing was 50 mm in the for- 

 ward quarter of the ship's length and 100 mm in the 

 remaining length. The appendages, i.e., the bilge keels, 

 rudder, propellers, propeller shafts and brackets as well as 

 supers! ructiu'e and deck ecjuipment, were omitted. 

 The model was free to heave and pitch and the.se motions 

 were metisured by potentiometers and recorded by an 

 oscillograph. 



Wave heights were measured electronically by a pair 

 of brass rods 5 mm (0.195 in.) in diameter and were 

 recorded on an oscillograph. 



Strain meters were of mechanical type with gage 

 length f)f 80 and 100 mm (3.15 and 4 in.). The relative 

 displacements of two legs of a gage affected inductances 



of two coils and were recorded on tin oscillogr;i])h. Sev- 

 eral strain meters were installed at the deck ;uid !)ottf)m 

 at seven locations tUong the model's length. 



The model's elastic properties were verified by a pre- 

 liminary bending test. The model .ship was supported 

 ;it two points and was loaded hy dead weights on the 

 deck. The dis|)lacement of the keel centerliiie was 

 measured l)y dial gages at both supporting points and at 

 ten suitably spaced locations. Fig. 28 shows the cal- 

 culated and experimental values of deflections under a 

 dead load of 100 kg applied at the points indicated. 

 "Calculated" vtdues represent the sum of the bending 

 and shear deflections and are based on the hundred 

 per cent effectiveness of all longitudinal members. 



The amplitudes of heaving and pitching as well as the 

 bending moments are shown in Figs. 29 and 30. The 

 first of these shows the variations of the indicated quan- 

 tities with wave height at zero ship's speed and the 

 second — with model speed. As this can be seen in Fig. 

 29, the amplitude of heaving motion is proportional to 

 wave height but the up-hetive is .some 20 per cent greater 

 than down-heave. The bow-up pitching amplitude is 

 ;dso proportional to wave height but the bow-down 

 one is increasing with the wave height. With the 

 steepest waves, h = L/19, the down-pitching is 30 

 per cent greater than the bow-up one. 



For very low waves, up to h = 100 mm = L/75, the 

 hogging and sagging moments are eciual. With the 

 increase of wave height, an added sagging moment de- 

 velops so that the hogging moment is diminished by it 

 and the sagging moment is increased. At the wave 

 height of 400 mm or L/19, the sagging moment is 40 

 per cent greater than the hogging one. The photo- 

 graphs, attached to Sato's paper, show that, at wave 

 height h = L/20. the water reaches the height of the 



