From Dragon Ball Encyclopedia, the ''Dragon Ball'' wiki
Goku, Kuririn, and Turtle Hermit each charge their own Kamehameha. They then fire them at the same time so that they merge into a one large Kamehameha, inflicting a huge amount of damage.
Goku, Kuririn, and Turtle Hermit used this attack in their battle against Doctor Uiro in Dragon Ball Z: The World's Strongest. It did not have any effect, however, because his metal armor withstood the blast.