Surfboard design introduced in 1972 by Malcolm and Duncan Campbell of Oxnard, California. The bonzer was one of the first boards to use three fins: a pair of toed-in, keel-like side fins, located in front of a standard center fin. The board also had two parallel concaves down the bottom rear half of the board.

The bonzer (period Australian slang for "bitchin'") was a hot surf media topic in 1973 and 1974, and pro surfers Ian Cairns and Jeff Hakman were among the design's proponents, saying the board was both faster and more maneuverable than the standard single-fin boards in use at the time. Bing Surfboards in California licensed the Campbell brothers' idea and put out a trademarked Bonzer model in 1973, but for reasons that aren't entirely clear the design never really caught on, and by 1976 it had all but disappeared. "The bonzer," surf journalist  Nick Caroll noted, "is without doubt surfing's greatest example of a surfboard design slipping through the cracks."

In 1975 Duncan and Malcolm founded a small commercial boardmaking interest, which later became Campbell Brothers Surfboards. An updated five-fin version of the bonzer was developed by the Campbell brothers in 1982 and later gained a small measure of popularity; California regularfooter Taylor Knox, one of the hardest-turning pros of the '90s and '00s, kept a couple of the new-age boards in his quiver. Mitch Thorson and Davey Miller were also bonzer devotees.

Variations on the double concave and the tri-fin board, meanwhile, became stantard on most high-performance shortboards. Simon Anderson, whose Thruster model is often cited as the first tri-fin board, is quick to credit the Campbell brothers for having arrived at the three-fin concept before he did.