Five sailors were missing after their dredger collided with a tanker off Singapore Wednesday, authorities said, just weeks after a deadly accident in the same area involving a US warship.A search effort was launched for the four Chinese members of crew and one Malaysian after the accident around the busy Singapore Strait, the city-state's MPA (Maritime and Port Authority) said.Seven other Chinese sailors were rescued from the Dominican-registered dredger after it capsized following the c