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If you look at our boat from above, you can see that each side has a curve similar to an airplane wing (or a car roof). As we move through the water, we displace the water ahead of us, it accelerates along the hull, and rejoins at the stern.
This creates a high pressure zone forward and a low pressure zone aft. In the process, the boat also creates turbulence. Turbulent flowing water is easier to swim through than non-turbulent (called laminar) water.
The four-foot +/- porpoise in this video (link to YouTube) has positioned itself in the turbulent low pressure zone and is actually being pulled along by the boat. It’s drafting, which is why we called it our NASCAR Porpoise. Watch how little it moves its tail to stay in position as we move forward.
We’ve had porpoise do this several times to hitch a quick ride from one end of their feeding area back to the other. They seem to favor the port side to the starboard. We have no idea why. Perhaps it is the sun, perhaps the propeller noise, perhaps the bubbles. Who knows?