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 1000m.
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 7.5–12°N, 113–117°E. The US NGA literatureetc. seems to consider its centre as Coordinates: .
The area is poorly charted, making it exceptionally dangerous to navigation – 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.
The boundary of Dangerous Ground is shown on NGA charts 93044 (NW), 93045 (NE), 93046 (most of the SE), and 93047 (SW). (The missing portion of the SE is covered by 93048 and the top corner of 92006.)
The area is described in NGA Pub. 161, Sailing Directions (Enroute) South China Sea and the Gulf of Thailand. Unfortunately, the navigational charts and sailing directions do not completely agree with each other as to the boundary. For example, the Sailing Directions include most of the NW area shown on Chart 93044 as outside of Dangerous ground, but exclude the Reed Bank, which is shown on Chart 93045 as inside Dangerous Ground.
Both publications divide the area into four quadrants - NW, NE, SE and SW:
Sailing Directions pp13–15. Other parts of the Spratly Islands which are not inside Dangerous Ground include:
The sovereignty of many of the islands is disputed, as are economic claims.