Tab Hunter darkened his hair and Peter Brown lightened his in order to better match the athletes who did the actual surfing for them.
Those shots of Fabian, Peter Brown and Tab Hunter--photographed from mid-chest up--riding their surfboards were actually shot on a sound stage at Columbia Studios. The actors balanced on Radio Flyer wagons in front of a rear-projection screen showing ocean waves. Assistants then sprayed them with water while maneuvering the wagons to give the desired effect.
Fabian shaved off his chest hair in order to give his torso a smooth look for his many "beefcake" scenes.
The Waimea footage in the movie was actually shot by the Napoleons, who traveled to Hawaii specifically to capture surfers taking on the giant waves. A series of weather conditions had come together to produce one of the longest uninterrupted periods of big waves in recent memory in late 1962 through March 1963. The Napoleons, equipped with these spectacular shots, went back to California and wrote the script around them.