124 THE EFFECT OF WAVES UPON A TAFFRAIL LOG. 
at 7.8 knots there were 8 crests so that in going from the former speed to the 
latter two crests have passed under the log and there should be two peaks to 
the log factor curve of Fig. 4 between 7.8 knots and 9.2 knots. Also at 9.2 
knots, according to Fig. 5, the log is nearly on a crest so the log factor 
should be nearly at the top of its upward variation; continuing in this way 
Fig. 4 is completed. 
So far only the stern system has been considered, now if the bow system 
be brought into the conception it injects a decided modification in the pre- 
"Gresham " 
Leg Towed £55' behind AP. 
' ! | ] ! ! = 
1 | Asia 
A'P 
ut 
I V= 92K 
n 
aie | | A> 47.0! 
Ar 
wt 
ZT Ve W./K: 
1 1 i { 1 a 
1 ! ' | { | x= 68.0 
Ar * 
ee eee 
q H | =sJ/olo’ 
4 | | 1 A=//070 
A'p. 
+. Y v= 203K 
[ A= 2390" 
‘2 x <2 ae ae 2 = ge 350! 
Sierh Ware System af Speeds at which 
Bow Ware u Super poses 
Fic. 5. 
ceding figure (Fig. 4). Asaship is propelled through the water at gradually 
increasing speed the bow wave system, when it reaches the stern, alternately 
increases and decreases the height of the transverse waves of the resultant 
stern system. If the bow waves were of equal height to the stern waves, 
at the time of their reaching the stern system, the resultant waves would 
be twice as high as the individual waves when the two systems came crest 
to crest and would be nil when they came crest to hollow. ‘The speeds of 
the ship at which these two events occur can be figured with reasonable 
