CHAPTER 1 
INTRODUCTION 
1.1 PROLOGUE 
In the summer of 1951, a group of research naval architects who were scheduled to 
be on board the cargo ship Nissei—Maru cruising the Pacific from Japan to the United 
States was discussing the design of a system for measuring, recording, and analyzing ac- 
tual ship performance data. Such a system was needed for the first large-scale 
cooperative test,! organized by the Japan Towing Tank Committee (JTTC) of the Society 
of Naval Architects of Japan (SNAJ) and scheduled to start at the end of the year, to pro- 
vide a basis for the post-World War II study of hydrodynamic ship performance in all the 
laboratories and universities in Japan. 
To find the relationships between ship’s propeller revolutions, shaft horsepower, 
modes of motion, rudder angle, and so on, we decided to record, simultaneously and as 
accurately as possible, as many elements of ship performance as possible. Such measure- 
ments would provide an overview of the response of the ship. Many practical limitations, 
such as budget constraints, had to be considered, however. In addition we didn’t know the 
real limits of the accuracy of these kinds of measurements, nor did we know how to 
choose the proper duration of observation times. After lengthy discussion, it was decided 
to record each type of measurement for three minutes. 
Very few naval architects at that time had a good knowledge of probability or of 
statistics. We did not know how to analyze the data taken at sea, and we did not know 
how to estimate the ensemble characteristics of performance from a single sample obser- 
vation. The simultaneous records of the averages of the 3—minute responses gave us 
valuable knowledge of actual sea performance, but we realized that simple averages 
sometimes cover or conceal important information. For ship oscillations, of course, mean 
values are not significant, but this author could not be satisfied with merely noting the 
average frequency and mean amplitudes. 
During the test, the author? was responsible for measuring the ship’s relative speed 
and developed a new type of ship speed meter, based on an idea of Dr. Shiha. This new 
meter measured the frequency of Karman vortices produced behind a triangular cylinder 
towed by the ship and gave instant indications of speed variations. Although the towing 
point was selected to minimize the effects of pitching, heaving, and rolling, these motions 
did affect the speed of the towed body. The objective was to eliminate the effects of all 
motions except surging and to derive from these records, by some method, the real varia- 
tions in the ship’s speed relative to the water. The author later found that an advanced 
technique of multiple input analysis would have been useful. 
After the test at sea, we continued to look for methods for analyzing the data and 
found a stochastic process analysis used in weather forecasting to predict temperature, 
humidity, precipitation, and so on. The author started at once to study time series analysis 
and tried first several kinds of periodogram analysis and then correlogram and spectrum 
analysis.? Because of the poor communications in the engineering and scientific fields in 
Japan at that time (even five years after the war) we had very little information about the 
outside world until 1954 and were unaware of the pioneering work of Dr. M. St. Denis 
