FAMILIES of the two Chinese tourists killed when a Patong jet-ski ploughed into a catamaran are expected to arrive on Phuket tomorrow.

The deaths of the young couple, Zhao Qiang and his wife Fang Chu, both aged 28, took the fatality toll on Patong jet-skis so far this year to three.

While mourning the deaths of the young couple, a jet-ski official pointed out today that the operator had in this case done all that could be expected to ensure the safety of the visitors.

The vice president of the Patong Jet-ski Association, Nucha Petchvimol, told Phuketwan: ''The jet-ski operator was told by the young man that he did not need instructions because he had ridden a jet-ski before.

''If the person hiring a jet-ski has never ridden one before, operators usually give them a short instruction course.''

Police believe the woman took the driver's seat of the jet-ski while the couple were at sea and was at the controls when the jet-ski crashed into the catamaran, killing them both instantly.

The Chinese tour guide who was leading the group of 11 that included the couple also appears to have acted with due diligence.

He told Phuketwan that the young woman had said she was not feeling well and asked to stay at the group's hotel while the rest of the group went snorkelling, and that her husband opted to stay with her.

The guide was shocked to learn that the couple had been killed while jet-skiing off Patong, instead of spending the day quietly at their hotel in the neighboring beach destination of Karon.

His party was due to fly to Bangkok today where they were to stay overnight before flying home to China as the parents of the dead couple fly to Phuket.

The overriding question of the legality of jet-ski operations on Phuket remains unanswered. If a family did sue, who would take responsibility for a habitual breach of Thai law?

The jet-skis have been permitted to function outside the law for more than a decade. Scams in which operators claim for contentious ''damage'' are still being reported, although perhaps not with the same regularity as before the introduction of an insurance scheme last year.

The deaths of the two tourists certainly adds weight to the argument of water safety experts who say the jet-skis and speedboats need to be restricted to areas free from swimmers - and, as this tragedy demonstrates, other hazards on the water.