  While the half-angle which encloses a Kelvin ship wave pattern is commonly
accepted to be 19.47 degrees, recent observations and calculations for
sufficiently fast-moving ships suggest that the apparent wake angle decreases
with ship speed. One explanation for this decrease in angle relies on the
assumption that a ship cannot generate wavelengths much greater than its hull
length. An alternative interpretation is that the wave pattern that is observed
in practice is defined by the location of the highest peaks; for wakes created
by sufficiently fast-moving objects, these highest peaks no longer lie on the
outermost divergent waves, resulting in a smaller apparent angle. In this
paper, we focus on the problems of free surface flow past a single submerged
point source and past a submerged source doublet. In the linear version of
these problems, we measure the apparent wake angle formed by the highest peaks,
and observe the following three regimes: a small Froude number pattern, in
which the divergent waves are not visible; standard wave patterns for which the
maximum peaks occur on the outermost divergent waves; and a third regime in
which the highest peaks form a V-shape with an angle much less than the Kelvin
angle. For nonlinear flows, we demonstrate that nonlinearity has the effect of
increasing the apparent wake angle so that some highly nonlinear solutions have
apparent wake angles that are greater than Kelvin's angle. For large Froude
numbers, the effect on apparent wake angle can be more dramatic, with the
possibility of strong nonlinearity shifting the wave pattern from the third
regime to the second. We expect our nonlinear results will translate to other
more complicated flow configurations, such as flow due to a steadily moving
closed body such as a submarine.
