HYDROGRAPHY 65 



V 

 Dangers 



CORAL AND ROCK REEFS AND LEDGES (A-lld-llg) 



Coral and rocky reefs and ledges are indicated on the charts by the sanae symbol. The 

 area between the mean high-water line and the outer edge of the ledge symbol should be tinted 

 green on the printed chart. The type of reef (rock or coral) is named when known. 



Reef or ledge symbols should be distinctly drawn so that they will reproduce satisfac- 

 torily on the printed chart. The symbols for reef areas less than Y^" in diameter, at the scale 

 of the chart, should be changed to a rock awash symbol. A reef or ledge symbol is used only 

 when the reef or ledge uncovers at low water. 



There is no distinctive symbol for a submerged reef or ledge, and where the limits have 

 been determined they should be indicated by a dashed line which encloses the sunken rock 

 symbols or the appropriate legend (See 0-1 0). Italic letters should be used for the legend 



A rocky reef is considered to be detached from shore, whereas a ledge is a rocky formation 

 connected with and fringing the shore. Italic lettering should always be used when ledges 

 are named. 



OYSTER REEFS (Pg. 69) 



Oyster reefs which uncover at the plane of soundings should be indicated by a low- water 

 curve and labeled, thus: "Oys". Submerged reefs, not adequately defined by soundings, should 

 be delineated by a short-dashed line properly labeled at frequent intervals. 



NAMING REEFS 



The style of type to be used in the naming of reefs surroimding an island is a cartographic 

 problem. In general, it is best to use italic lettering when the reef predominates, and roman 

 lettering when the island predominates. 



RIPRAP MOUNDS (K-Ka) 



At many light structures on the East coast, riprap mounds are maintained to protect the 

 structures against ice damage or scouring action. 



As a warning to small craft, all known riprap mounds shall be clearly charted, using the 

 scallop-like symbol for rock (Symbol Sheet, A-lld). In most instances this will require ex- 

 aggerating the outer limits of the riprap so as to extend them beyond the light symbol's 3-mm. 

 magenta disc. 



On charts of the l:80,000-scale series where these riprapped lights are not charted, a rock 

 awash symbol shall be shown in the position of the light structure. 



When the riprap symbol is charted, the following caution note shall be added to the notes 

 of that chart: 



CAUTION 

 Mariners are warned to stay 

 clear of the protective riprap sur- 

 rounding navigational light struc- 

 tures shown thus: c*'^ 



