The city's highest court could decide how ships navigate in one of the busiest stretches of Hong Kong's waters following appeals against conviction by two seamen involved in a deadly ship collision four years ago. Eighteen crew on board the oil rig supply ship Neftegaz-67 died when it capsized and sank after it collided with the larger dry cargo bulk carrier Yao Hai near the Brothers Islands off Lantau on March 22, 2008. Seamen onboard the Neftegaz-67 thought they were sailing in open water, while the Yao Hai crew believed they were transiting in a narrow channel, which meant different navigation rules applied. Yuriy Kulemesin, the Ukrainian captain of the Neftegaz-67, and Tang Dock-wah, chief pilot onboard the Yao Hai, are asking the Court of Final Appeal to overturn their convictions on charges related to endangering life at sea. Both men had their jail terms cut at the Court of Appeal in December 2011. Kulemesin, who was originally jailed for three years, two months, had his sentence reduced to 18 months. Tang Dock-wah was freed after his three-year term was cut to the time he had already spent in jail. Kulemesin is appealing his conviction on the grounds there was no mens rea, or knowing intent, in breaking safety at sea rules, and he was sailing in open water not a narrow channel. Nigel Jacobs QC, appearing for Kulemesin at the start of the appeal yesterday, said marine traffic regulations, geographic features and water depth would determine whether a section of water was considered a narrow channel. He noted that while fairways, or shipping channels, were marked on government charts of Hong Kong waters there was no narrow channel marked in the part where the collision occurred. Jacobs said a series of buoys in the area "denotes a deep water route" not a narrow channel. Non-permanent judge, Lord Clarke of Stone-cum-Ebony, queried whether all navigation features were marked on charts. Jacobs said courts could "step into the breach" with a ruling if there was confusion over a body of water. The hearing is scheduled to last four days.