The image of a Chinese junk with its distinctive, vibrant red sails floating in  Victoria Harbour is a symbol of Hong Kong recognised around the world. But the boats traditionally used in Chinese waters since the Han dynasty (206BC-AD220) have all but disappeared. Only one authentic junk, the Dukling, is still sailing in Hong Kong today. Now even that last survivor is under threat from the Covid-19 pandemic, as passenger numbers crash to 90 per cent below normal, and few if any foreign tourists…