>>8883480 LB

>Having that in mind, would ground-effect boatplanes be detectable on active sonar?

No. This is moar complicated. Active sonar "pings" do some pretty unusual things under water. And yes, they can travel outside of water, but there isn't enough strength of signal for sound to travel from water to air, back into water and then return to a distant transducer with enough strength for detectability. Even passive won't do that to any usable tracking value.

>AFAIK when the sound wave changes mediums (from sea to air), it changes its angle depending on the density.

Correct. Sound can reflect off of the boundary between mediums, refract through it, scatter or just be lost to absorption - actually sound vibrations will do all at once - some through, some back to you, some elsewhere and some just dissipate.

>Also, can you listen passively while active sonar is pinging?

Yes. Passive sonar can be set to listen to (or exclude out) certain frequencies. Active sonars transmit only in a set range of frequencies. So...