Wake speed

[TiggerToo]

At what speed to wake waves travel?

 

[duncan99210]

I googled ship wake propagation and found many learned papers on the topic. Presumably the answer is buried in them but I lost the will to live after the first page of the first one......

 

[sarabande]

boats produce different sorts of waves (height, steepness, wavelength between crests, etc) and these variations influence the speed and angle at which the waves move away from the centreline of the wake. Empirically, you can see how the shallowness of the water also changes the normal shape and angle of the boat's wake as the reflected pressure waves change the angle and depth at which the boat moves (known as "squat").

Generally the angle at which wakes waves move away from the wake centreline starts at just under 20 degrees, so there is a geometrical relationship with the boat speed . Waves with greater distances between crests (wavelength) travel faster than short ones, so the longer (bigger) waves move away faster than small waves.

[/IMG]

 

[Lon nan Gruagach]

You also got the really screwy bit where the waves travel faster than the wave packet.

 

[sarabande]

sometimes the packets disperse, sometimes they don't. There's more physics in that than I can deal with on a Sunday morning

 

[snowleopard]

The speed of a wave is proportional to the square root of the wavelength. I was amused by a comment in Tracey Edwards's book about her RTW race that 'waves travel at 22 knots'. A ripple on a pond might do 1 knot, a tsunami typically hundreds of knots.

Here's a formula: http://hyperphysics.phy-astr.gsu.edu/hbase/waves/watwav2.html Note that the depth factor is insignificant once the depth is more than a few wavelengths.

 

[johnalison]

boats produce different sorts of waves (height, steepness, wavelength between crests, etc) and these variations influence the speed and angle at which the waves move away from the centreline of the wake. Empirically, you can see how the shallowness of the water also changes the normal shape and angle of the boat's wake as the reflected pressure waves change the angle and depth at which the boat moves (known as "squat").

Generally the angle at which wakes waves move away from the wake centreline starts at just under 20 degrees, so there is a geometrical relationship with the boat speed . Waves with greater distances between crests (wavelength) travel faster than short ones, so the longer (bigger) waves move away faster than small waves.

[/IMG]

Which is presumably why the wake itself in your photo appears curved, as the waves flatten out and lengthen, they actually speed up. I wonder what would happen in an infinite lake. Would a boat's wake eventually overtake the boat?

 

[sarabande]

depends if the boat speed is greater than the theoretical speed of the wavelength of the big waves. But by they time they are catching up, the crest height will be very small, as the energy of the boat is dispersed over an ever lager area. (Ooops. "larger", of course !)

 

[johnalison]

depends if the boat speed is greater than the theoretical speed of the wavelength of the big waves. But by they time they are catching up, the crest height will be very small, as the energy of the boat is dispersed over an ever lager area. (Ooops. "larger", of course !)

I believe that some tsunami waves travel at extremely high speeds. In my infinite lake, I am supposing that the wake waves would increase in wavelength until they approach this level. Maybe.

 

[aquaplane]

When my parents went up the river Plate on a container ship they said it was really easy to tell where the edge of the dredged channel was. There was a crook in their wake as it accelerated in the shallower water.