Modern daylight piracy!

What is an act of Piracy? Is it the forceful attack that qualifies it as piracy or is it a deliberate act of deceit or theft that qualifies it and can it be classified as piracy act by a yacht owner if he doesn't pay the skippers delivery fees? A friend recently delivered a boat from Pt Moresby to Darwin with a very inexperienced owner onboard. They had agreed on a price plus a return airfare to Papua New Guinea when the delivery was completed. When they arrived in Darwin the boat was removed from the water for repairs. The skipper purchased a air ticket to NG and gave a copy of the invoice to the owner. Who said he had no money at that time (Where have I heard that before) and would go to the bank and get his wife in the UK to send him the money. He also asked the skipper to lend him an additional amount of $500 to get a new cutlass bearing for his yacht and he would reimburse him when his money came through. Returning to NG with the whim and a promise of payment to be deposited in his Aussie bank account may of been his big mistake. So his big question to our readers - Is once the owner left Australia and headed to Kupang with the Sail Indonesia fleet has he committed an act of piracy or is it a criminal offence to abscond without payment or just deceitful conduct on his behalf?