I used to fish a plug like that for sperm whales when I lived in Hawaii. Made the diving lip from the hood of a 1959 Plymouth Fury and used manhole covers for belly weights. I bought a surplus catapult from an aircraft carrier that would throw the thing about a quarter of a mile. The feds shut me down when the damn thing hit the periscope on a Trident submarine and snapped it clean off. Too bad; I'd just gotten it tuned so it would swim like a giant squid.