here in Palawan and other parts of the Philippines i've seen boatmen/ guides that have excellent free diving skills. they only use home made fins called as Padyak/ pamadyak (stomp/tread) it's made out of thick ordinary black rubber straps (like the one you get from hardware shops) and a piece of plywood shaped like a large plate. sometimes they use two but most of the time i see only one piece. they dive deep w/ no effort and stay underwater longer. they also use home made spear guns.... again just w/ rubber bands, wooden stick and a metal/ stainless spear... heck, even their goggles are made of wood, thick rubber bands and plain glass...