The accident took place in the QEII Marina at about 4.30pm and saw all the emergency services respond.
It was decided to lift the man to safety after he had been placed on a stretcher in the boat.
St John Ambulance Service acting station officer Stuart Malley explained what had happened.
'A 71-year-old male had fallen off a ladder onto a boat, sustaining lower back injuries. He has been immobilised on spinal equipment, given pain relief at the scene and transferred to A&E.
'His injuries are not believed to be life threatening.'
