The non-competitive adventure activity of riding the biggest waves possible (known as "rhino hunting") is popular with some surfers. A practice popularized in the 1990s has seen big wave surfing revolutionized, as surfers use personal watercraft to tow them out to a position where they can catch waves previously unrideable because of the speed at which they travel (see tow-in surfing). Some waves reach speeds of over 60 km/h; personal watercraft enable surfers to catch up to the speed of the wave, thereby making them rideable. Personal watercraft also allow surfers to survive wipeouts. In many instances surfers would not otherwise survive the battering of the "sets" (groups of waves together). This spectacular activity is extremely popular with television crews, but because such waves rarely occur in heavily populated regions, and usually only a very long way out to sea on outer reefs, few spectators see such events directly.