Sea spray

On my way home from Berlin I was sitting on the fast boat travelling North from Bergen watching the spray fly past the window. Tired after the workshop and travel, I wasn't quite thinking straight and started to wonder how the spray was thrown backwards by the bow of the boat. Of course it isn't, it's the boat going forwards through the spray. You can see the droplets elongated into short lines in the photo. It was strange how sometimes they were there and other times not. The path didn't look particularly parabolic but it was rather distorted by perspective. The boat was travelling about 20 knots which is 27kmh^-1 or 7.5ms^-1. the spray was shooting up to about 3m and landing about half way along the boat which was 45m long.

From the height the time of flight can be found to be1.6s.  In this time the boat will have moved forward 12m which isn't as far as I observed. I guess there must have been a wind blowing against the direction of the boat which would explain why the spray wasn't always present. To get the spray to reach 20m the relative velocity would have to be around  12.5ms^-1 implying that the wind was blowing the water at 5ms^-1 which seems reasonable. I thought I'd try to make an animation of the spray by projecting balls upwards as a boat went past. I tried with springs but it didn't work so settled for bouncing balls.

I thought this made an interesting wave pattern which has a repeating parabolic shape as opposed to a sine wave. The water droplets don't bounce off the water of course but it gets the idea across.

Since Interactive Physics allows you to change the frame of reference I though it might be neat to see what it looked like from the frame of reference of the boat.

Yep, looks just like sea spray.