THE EFFECT OF WAVES UPON A TAFFRAIL LOG. 123 
gradually increased its speed. These variations would correspond to the 
successive traveling of hollow and crest past the log, as the transverse waves 
behind the ship gradually lengthen with the increasing speed, and if a plot 
were to be made of this log factor, on speed of the ship as abscissz, it would 
have the general appearance of Fig. 4, which is made for a log towed 255 feet 
behind a ship of 188 feet length between perpendiculars. 
Fic. 3. 
--.. The construction of this curve can be made evident by looking at Fig. 5 
which shows the stern wave system (according to the trochoidal wave theory) 
of a ship of the above length at several speeds. At the first speed (7.8 knots), 
the log is in a hollow so the log factor (the factor the log speed is multiplied 
by to get the correct speed) is below the normal value for still water. If 
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Fic. 4. 
A-B in Fig. 4, represents this still water value then the curve of Fig. 4 would 
begin with a hollow at 7.8 knots. Referring again to Fig. 5, at 9.2 knots 
speed there are but 6 wave crests between the log and the stern post while 
