Stunned Graeme Pullen and Wayne Comben became surrounded by a pack of blue sharks off Falmouth in Cornwall.
Two of the sharks — which have been known to kill humans – took it in turns to charge the 17-foot boat and ripped open a bag of fish hanging over the side.
Graeme, 60, managed to film the ferocious three-minute attack.
He described the three sharks as being in a frenzied state and he motored back to port as more of them started approaching his small boat.
Experts believe sharks are coming closer to land to hunt for food after years of commercial fishing has left the Atlantic drained of vital fish stocks.