The Nautical Chart


Lighthouses and other fixed lights use a basic symbol that appears as a black dot with a magenta “flare” giving much the appearance of a large exclamation mark (!). Major lights are named and described; minor lights are described only.

Daybeacons are indicated by small triangles or squares, which may be colored to match the aid. Daybeacons, also commonly called day marks, are always fixed aids. That is, they are on a structure secured to the bottom or on the shore. They are of many different shapes.

Prominent landmarks, such as water towers, smoke stacks, and flagpoles, are pinpointed by a standard symbol of a dot surrounded by a circle. A notation next to the symbol defines the landmark’s nature. The omission of the dot indicates the location of the landmark is only an approximation.

Wrecks, Rocks, and Reefs are marked with standardized symbols, for example, a sunken wreck may be shown either by a symbol or by an abbreviation plus a number that gives the wreck's depth at mean low or lower low water. When a dotted line is used around any symbol it calls special attention to its hazardous nature.

A system of abbreviations used alone or in combination, describes the Bottom Characteristics allowing selection of the best holding ground when anchoring. Knowledge of bottom quality is very important in determining an anchorage.

Shorthand representations have been developed and standardized for low-lying Structures such as jetties, docks, drawbridges, and waterfront ramps. Such symbols are drawn to scale and viewed from overhead.

A chart is only as accurate as the survey on which it is based. Major disturbances, such as hurricanes and earthquakes, cause sudden and extensive changes in the bottom contour. Even everyday forces of wind and waves cause changes in channels and shoals. The prudent boat operator must be alert to the possibilities of changes in conditions and inaccuracies of charted information.

Compromise is sometimes necessary in chart production as various factors may prevent the presentation of all data that has been collected for a given area. The information shown must be presented so that it can be understood with ease and certainty.

In order to judge the accuracy and completeness of a survey, the following should be noted:

The source and date of the chart are generally given in the title along with the changes that have taken place since the date of the survey. The earlier surveys often were made under circumstances that precluded great accuracy of detail.

Until a chart based on such a survey is tested, it should be regarded with caution. Except in well-frequented waters, few surveys have been so thorough as to make certain that all dangers have been found.

Noting the fullness or scantiness of the soundings is another method of estimating the completeness of the survey, but it must be remembered that the chart seldom shows all soundings that were obtained. If the soundings are sparse or unevenly distributed, it should be taken for granted, as a precautionary measure, that the survey was not in great detail.