This is an excellent resource from the Ventura County Sheriff’s Search and Rescue Dive Team.
“There are a variety of search techniques that are applicable to the underwater environment. While in theory, some patterns based on land or air search patterns should work. . . . in practice they prove to be inadequate underwater due to such factors as limited visibility, chaotic bottom contour, and submerged hazards. Experience has shown that to be efficient underwater a search pattern must be simple. The simpler – the better.”