Why do boats leave a flat mark in the sea after they've gone over it?

Question

Like when a boat goes over the tide the water just stays flat and takes ages for the wave to get into the flat area.

Answer 1

It is called the 'wake'. Not to be confused with the waves that roll away from each side of the vessel as it moves, which are called the 'wash'. The wash is caused by the displacement of the vessel. Not the wake.

As the vessel moves through the water it displaces the water (moves it out of the way). The wash is the visible evidence of this.

The wake - the path left astern (behind) the vessel is the area of turbulent water from which the wash has been displaced. It is even more turbulent behind powered vessels than sailing boats because of added turbulence from the propellor/s. And it becomes less and less turbulent with time following the passage of the vessel.

But even after a considerable time has passed the turbulence is still in the process of dispersing - getting back to 'normal'. And the calm, or as you say, "flat" area is the visible evidence of this process: An area of turbulance IN THE PROCESS OF returning to equilibrium. It is more noticeable when the water around it is a bit 'choppy'.

Answer 2

propwash

Answer 3

so they can find their way home...(:P)

Answer 4

because the 'waves eminating from the boat are initially stronger than those of the sea in the very immediate area.

Answer 5

not really a flat spot more of a smoothed area from where the water was displaced and the wakes were formed off the sides any way the small caps are formed by currents and wind ever see the sea in a storm ?  the water won't be flat during  a storm

Answer 6

displacement i.e.the gross weight of a vessel determines the quantity of water it displaces on its passage through said water. the markings left astern are caused by water refilling the space created by the vessel on its passage. the heavier the vessel the higher the wave.

Answer 7

Interesting I never noticed that

Answer 8

When the enginges are on any speed they obviously move so they do it because they're moving under the water. ur welcum

Answer 9

when a boat churns the watter that water becomes oxygenated makeing wher the ship or boat was seem to leave a trail. this is only common on still or smooth water.

Answer 10

water displacement beneath the ship