A 31-year-old Massachusetts man was thrown 20 feet into the air when his personal watercraft exploded on Saturday at a marina on Long Lake in Naples. Karl Marchionda of Danvers had just fueled up his watercraft at around 4:50 in the afternoon and was trying to start it when a spark ignited vapors in the hull of the vessel, said District Game Warden Neal Wykes. Officials are still trying to determine the source of the vapors, he said. The blast sent pieces of the watercraft flying, and launched Marchionda face-first onto the dock, said Wykes, who said he arrived about five minutes later. Marchionda had several broken ribs and two fractured vertebrae, as well as abrasions and lacerations to his face, said Wykes. He was taken to Bridgton Hospital.