I get the impression from what I have read that, for a simple moving wave train on water,
X = horizontal rest coordinate of a bit of the water surface,
x = horizontal displacement of a bit of the water surface,
y= vertical displacement of a bit of the water surface,
t = time
a = amplitude/2
b = constant
c = 2*pi/wavelength
f = constant
speed of waves varies as sqrt(wavelength)
x = a*sin(b+c*X-v*t), y = a*cos(b+c*X-v*t), v=f*sqrt(c) :: eqns (1)
This leads to a hypocycloid with the sharper curves on top.
If a is too big compared to 1/c, the curve becomes an epicycloid with loops on top, but water cannot go through itself, so the waves develop foam crests (sometimes called "white horses").
I have been unsuccessfully trying to make equations (1) into a differential equation. Please is there known a differential equation, or set of differential equations, for waves moving on the (2-dimensional) surface of 3-dimensional water, including explaining the usual mixed disorderly wave patterns seen on water in nature?