Every year, more than 3,600 commercial ships - oil tankers, cruise liners and cargo ships - sail into San Francisco Bay, and their captains face an obstacle course of dangers.

'Captains go on full alert as soon as they begin to approach the bay,'said Bob Bea, a former oil tanker captain who sailed off California from 1989 to 1995.

'It's even more nerve-racking once they get in the bay. There are so many ferries and sailboats and bridges that their biggest fear is hitting something.'

Last week's oil spill from the Cosco Busan underlined the risks. And despite better technology and increased safety rules that have been put in place since the 1989 Exxon Valdez spill, significant hazards for the behemoth ships remain.