186 



THEORY OF SEAKEEPING 



tion of keel stresses during one cycle, and also during a 

 period of about 270 sec. It can be observed that the 

 irregularity of ship-stress \'ariations is similar to the 

 irregularity of accelerations. Kenipf and Hoppe com- 

 mented on the fact that simultaneous measurements of 

 strains and accelerations are necessary for a complete 

 anali'sis of ship stresses. Howe\'er, the means for such 

 simultaneous measurements were not a\-ailable. Table 



Table 3 Range of Stress in Longitudinal Members (from 

 Kempf and Hoppe, 1926b) 



All stresses (item 1 to 9) in kg/cm =. 



Item 10 — deflections of ship ends in centimeters. 



3 shows the maxinimn range of stress (hogging plus 

 sagging) as measured by Kempf and Hoppe. The authors 

 called attention to the fact that the stresses cau.sed bj' 

 different ship loadings while in port are of the same order 

 of magnitude as the stresses caused by waves at sea. 

 The waves met on this voyage of the SS Hamburg were 

 20 ft high and 425 ft long, corresponding to a wind 

 strength of 9 on the Beaufort scale. Kempf and Hoppe 

 expressed the opinion that these waves and the resultant 

 ship stresses represented a degree of severity not likely 

 to be greatly exceeded in the ship's normal service. 



5.12 Voyage of the MS San Francisco. In 1934 Dr. 

 Georg Schnadel organized an observational \'oyage on 

 the well-instrumented MS San Francisco. Descriptions 

 and results of the \'o.yage were given by several partici- 

 pants as follows : 



Schnadel (1936, 1936/37, 1938)— General Descrip- 

 tion and Ship Stresses. 



Horn (1936) — Ship Motion and the Instrumentation 

 Used in This Connection. 



Weiss (1936) — Instrumentation for Measurement of 

 Wave Contours on Sides of a Ship. 



Weinblum and Block (1936) — Stereophotographic 

 Measurements of Wave Contours. 



Later the hydrodynamic properties of this ship were 

 investigated by Kempf (1936) in a towing tank. 



The MS San Francisco is a .shelter deck cargo ship of 

 13,070 tons displacement, 130 m (426.5 ft) long BP, 

 with a 18 m (59 ft) beam, a 6.9 m (22.6 ft) draft forward, 

 and a 7.61 m (25 ft) draft aft. The block coefficient 

 is 0.744. This ship was chosen because of its simple 

 design. The strength deck is continuous through a 

 large part of the ship's length, and only a light super- 

 structure is located above it. The space between the 



weather deck and the strength deck provided acces- 

 sibility for installing strain gages on both sides of the 

 strength deck. A two-stroke-cycle five-cylinder MAN 

 engine deli\-ered 4200 metric horsepower at 90 rpm and 

 gave the ship a 13.2-knot speed in smooth water. 



The instrumentation used for measuring the ship's 

 motions consisted of a gyroscopic apparatus for record- 

 ing pitching and rolling angles and several types of ac- 

 celerometers for measuring vertical accelerations. The 

 locations of these are shown in Fig. 26. 



A wide \ariety of accelerometer types was employed 

 to fill special needs. An attempt was made to obtain a 

 specially designed long-period accelerometer for deter- 

 mining heaving motions. Accelerometers of lesser ac- 

 curacy were available for this purpose. Also needed 

 were accelerometers capable of recording for long periods 

 of time at not readily accessible locations. A thorough 

 discussion of the accelerometer theory was given b.y 

 Horn (1936). 



The wave profiles on both sides of the ship were de- 

 termined by means of electric contacts (Weiss, 1936). 

 The contacts were installed at six positions along the 

 length of the ship as shown in Figure 27. At each posi- 

 tion one contact, was placed at the edge of the keel and 

 16 contacts located at equal vertical distances apart were 

 installed on the starboard and port sides. Sea water 

 in rising waves closed the contacts and lighted signal 

 lamps. These lamps left traces on a film in a special 

 recording apparatus. The wave profiles on both sides 

 of the ship were constructed from the wave height taken 

 at the longitudinal six locations. It also was possible to 

 estimate the shape of a wave longer than the ship by 

 extrapolation of the recorded profile. 



The voyage was made from Hamburg to Vancouver 

 and back, with both crossings taking the ship through 

 the Panama Canal. On the outgoing voyage the ship 

 was lightly loaded, but it was fully loaded on the home- 

 ward voyage. Throughout most of the voyage the 

 weather was light, but two uiuisually se^'ere storms 

 were encountered in close succession during the home- 

 ward journey in the eastern North Atlantic. The first 

 lasted from 11:15 am on December 11 to 2:15 am on 

 December 12.-^ The second from 11 :40 am to 1 :37 pm 

 on December 14 and 4 pm on December 14 to 8:15 pm 

 on December 15. Schnadel (1936) emphasized the fact 

 that the first storm developed very rapidly — the highest 

 waves were reached in 4 or 5 hr. The wind, described 

 as of 9 to 11 strength on the Beaufort scale, reached 12 

 for a few hours. At the beginning of the storm the ship 

 was traveling with the wind. At the height of the storm 

 the ship hove-to with the bow against the wind and sea. 

 The largest waves reached a height of 52.5 to 59 ft, as 

 shown by the extrapolation of the wa\-e profile at the 

 ship's side and by stereophotographic measurements. 

 By eye from the bridge the waves were seen to be at least 

 49 ft "high. 



Fig. 28 shows a sample of the ship's motion record in 



2' This statement of the time is needed in connection with 

 Tables 4 and 5. 



