Devn 



In spite of the care taken , it happens that , under cer - 

 tain conditions one observes vertical motions which differ much 

 from sinusoidal motions . It is then necessary in order to study the- 

 se vertical motions to use the method described in the following 

 paragraph . 



2, 23 - The quantity s (t) is measured by means of three 

 capacitance probes similar to that used to measure the wave height . 

 Figure 6 presents a sketch of the corresponding set-up . Each probe 

 gives a signal proportional to the submerged length of wire , thus 

 the sum of the three signals gives a value proportional to s (t) provi- 

 ded that the pitch angle be small , which was the case in the experi - 

 ments performed (see above paragraph) . The value of s (t) is then 

 related to that of the heave Z (t) by : 



s (t) = z (t) - r (t) 



2, 24 - The pitch and roll angles were measured separa - 

 tely with a Polaroid camera : a picture taken during a time intervall 

 equal to one period of the motion gave the extrem angular positions of a 

 little rod set on top of the model . 



2, 25 - The interest of these methods is that they leave 

 the model completely free except for a few very thin electrical wires 

 going from the accelerometer and wave probes . 



Ill - EXPERIMENTS PERFORMED IN REGULAR WAVES - 



The experiments were conducted partly in the wave tank 

 of the Bassin d'Essais des Carenes (dimensions : 30 m x 7 m x 

 2.40 m) and partly at the towing tank n° 2 (dimensions : 1 50 m x 8 m 

 x 2 m) . In both tanks the possible waves are f w ^ 0. 30 m. , 

 0.20 Hz ^ f < 1Hz . 



Two types of experiments were performed 



- The model was completely free to move in all directions to study 

 the rolling . 



- The model was forced to stay in a vertical plane parallel to the 

 direction of wave propagation in order to study its vertical 

 motions and its pitching motion . 



IV - EXPERIMENTS IN REGULAR WAVES WITH A COMPLETELY 

 FREE MODEL : STUDY OF ROLLING - 



The experiments in one -directional regular waves with 



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