Li Du was initially prepared to fly to Melbourne. He wanted to leave his parents and the rest in Melbourne to have fun. Then he would continue his flight towards Hobart, the capital of Tasmania, to finalize his island purchase.
Now that he had a huge yacht, he had changed his mind. He decided to spend some time sailing and take his yacht to Hobart. That way, nobody would have to split up, and they could all have fun out in the sea together.
Besides, the Martins were still suffering from their summer cold. For them, it might be better to avoid flying. It would be healthier for them to keep warm and set off through the sea.
It was summer in Australia and hence, the sea would not be cold at night.
As the Martins did not have much to do when they were hospitalized, they had been watching the news. Hence, they had seen the news of the scam. After all, that had been the biggest crime that had happened over the past two days in Sydney.