Waves . 17 
along with the vessel. The bow waves are always at an angle 
of about 19%° with the fore and aft line of the ship. This is a 
‘surprising fact because it would seem natural to expect the 
angle to be sharper the faster the ship moved. Yet the the- 
oretical study of ship’s waves shows clearly that this angle 
ay = : : Be 
Official U.S. Navy Photo 
PT traveling in the wake of a sister ship. Stern waves can be seen 
radiating from wake. 
must always remain constant and independent of the ves- 
sel’s speed. 
Directly following the rudder and screw, the water will 
be observed to be in a very disturbed state, another example 
of turbulent fluid motion. Under certain circumstances the 
first stern wave appears so large that it seems almost threat- 
