A naval architect said yesterday he had never heard of a law allowing lifebuoys to be shared by two people, as suggested by the owner of the sunken ferry Lamma IV.

Dr Neville Armstrong also told the commission of inquiry into the October 1 sea tragedy that Britain and Australia required ships to carry enough life jackets for all passengers. Child-sized vests also had to be provided.

A general manager of Hongkong Electric, which owned the Lamma IV, has testified there were 65 lifebuoys - one for every two people - and 92 vests on board. Francis Cheng Cho-ying said the devices, along with a life raft big enough for 10 people, were enough for the vessel's maximum capacity of 232 people.

Armstrong, appointed as an expert witness by the commission, said he had never seen regulations allowing lifebuoys - which are designed to be thrown to people in the water - to be shared. "I have never come across other jurisdictions [in which] buoys could also be life-saving apparatus on board your vessel," he said.

He also noted that such a small life raft had little value.

The Lamma IV was carrying 127 people, including three crew, on the night of the National Day when it collided with the public ferry Sea Smooth. At least 28 of the 39 who died were not wearing life jackets, while four were holding vests in their hands.

Armstrong said it was difficult to say when boat staff should demonstrate how to don life jackets as it might not be practical on certain vessels.

But even if there had been a demonstration it would not have solved the problem of the long tapes on the Lamma IV's lace-type vests, which could easily tangle around the legs of seats, the Australian expert added.

He also said new buckle-type vests the company planned to introduce on two vessels now under construction posed potential hazards.

Armstrong cited an accident investigation he had been involved in concerning a vessel called the Sleipner in Norway. Two of the six victims died because their buckle-type vests had floated over their heads after they jumped into the water.

He also had noticed the button on the horn of the Lamma IV was rusty and so it might not have sounded when pressed.

Armstrong accused the Marine Department of negligence because the Lamma IV did not have a watertight door, which meant it flooded quickly and sunk. He was surprised and disappointed that a vessel designed for more than 200 passengers had been allowed in service without a watertight door, as it was originally designed to have.

Armstrong suspected there had been a lack of communication between officials making the design decisions and the inspectors out in the field.

It was "widely known in the industry" that the absence of watertight doors had caused the loss of many vessels.

The hearing continues today.