Dangerous Ground (South China Sea)

Dangerous Ground is a large area in the southeast part of the South China Sea characterized by many low islands and cays, sunken reefs, and atolls awash, with reefs often rising abruptly from ocean depths greater than 1,000 metres (3,300 ft).

There are few precise definitions, but Dangerous Ground corresponds roughly to the seas around the eastern half of the Spratly Islands. It is an oblong area running southwest to northeast for about 340 nautical miles (nm) (630 km), 175 nm (324 km) at its widest, with an area of about 52,000 nm² (178,000 km²). It is west of Palawan island and northwest of the Palawan Passage. It lies approximately between 7.5 and 12°N, 113–117°E. The US NGA literature^etc. seems to consider its centre as 10°N 115°E.

The area is poorly charted, making it exceptionally dangerous to navigate – the major Singapore-to-Hong-Kong routes go well to the west and east of the area. The Admiralty Sailing Directions give the following warning regarding navigation in this area:

Due to the conflicting dates and accuracy of the various partial surveys of Dangerous Ground, certain shoals and reefs may appear on one chart, but not on another regardless of the scales involved.
Charted depths and their locations may present considerable error in the lesser known regions of this area. Avoidance of Dangerous Ground is the mariner’s only assurance of safety.

The water is a usually greenish-blue and is transparent to depths of 24–42 metres (79–138 ft) on clear days.