I just saw this video of some huge killer whales riding a boat’s wake. Does having a killer whale (or a surfer, or a dolphin) riding your wake cause your boat to use more energy to drive through the water than it would without a killer whale in tow? Or is the killer whale drafting on energy that would otherwise dissipate into the ocean? How about on the bow wave?
In: 6
No, the ship does not expend more energy or lose speed.
The bow wave is energy the ship already imparted to the water propagating away from the point of interaction. The wave carries on until internal, atmospheric, and shoreline friction convert the energy into heat.
The whale/dolphin harnesses some of this energy to move itself along. The result is that the wave dissapates a little sooner than it otherwise would have.
No. A dolphin IN a wave has pretty much the exact same mass as the water that would’ve been there otherwise. So the ship is pushing the same amount of mass either way.
(Nitpicky answer: Technically when the dolphin swims into or out of the wave, it brings a tiny bit of energy with it that could push or pull harder against the boat, but when “coasting” in the wave, it’s effectively zero difference to water alone.)
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