262 



THEORY OF SEAKEEPING 



10 10 30 40 

 Meter 



50 



C 



DE 



Pressure at Hogging Condl+lon 



Wave Contour 



Pressure caused by Wove (Midship) 

 Pressure caused by Wave (Side of Ship) 

 Influence of Oscilla+ion and of added 

 mass, Heaving and Pitching 



Fig. 4 Pressure in hogging condition (from Schnadel, 1937- 



1938) 



itself and the iiiiluciicc of the added mass of water in the 

 case of heaving and pitching." 



The measurements of water pressures and uf hea\-ing 

 and pitching accelerations provided the necessary data 

 for the construction of the load-distribution curves. 

 These are shown in Kig. 6 for the hogging conditions. 

 By the usual integration the diagrams of shear forces 

 and of bending moments, shown in I'ig. 7, were obtained. 

 Schnadel commentetl on these as follows: 



"For the accurate knowledge of the ship's stress in a 

 rough water, it is important to separate the influences 

 of dynamic and static forces. The dynamic forces con- 

 tain two different parts: the forces resulting from the 

 acceleration at the hull and the acceleration of the added 

 mass. The load curve of the first part results from the 

 difference of the acceleration forces on the ship's mass 

 and the change of the buoyancy caused by the heaving 

 oscillation. For the hogging ship the bending moment 

 is reduced by the dynamic forces. 



46 



10 20 30 40 

 Meter 



50 



Fig. 



Pressure at Sagging Condition 



A Wave Contour 



B Pressure caused by Wave (Midship) 

 C Pressure caused by Wave (Side of Ship) 

 DE Influence of Oscillation and ot added 

 mass, Heaving and Pitching 



5 Pressure in sagging condition (from Schnadel, 1937- 

 1938) 



"Calculating the second part, we obser\'e that the 

 forces of the added mass carry a part of the ship's weight 

 instead of the corresponding buoyancy. The load dia- 

 gram is therefore the difference between the forces of 

 the added mass and the buoyancy curve of the corre- 

 sponding tliving. This load cau.ses, in general, a bending 

 moment which increa.ses the statical moments. 



"Consider ¥\g. 7, which shows the static and dynamic 

 hogging moments; it is to be seen that the influence cal- 

 culated as described is very different at the midship 

 section and at the ends. The results for the midship 

 section are as follows: 



Static hogging moment as in- 

 fluenced by sea -|-.')0,(K)0 metre-tons 



Dynamic moment as influenced 



by sea (ship hove to) — 7,500 metre-tons 



Ivesultant moment 4-22,500 metre-tons 



This moment is measured from 



the moment of still water con- 



(.liticjii -|- 2:3,000 metre-tons 



