Symbols That Shout “Danger!” and “Beware!”
Learn to recognize rocks, coral, wrecks, and obstructions at a glance on your chart. Some rock symbols are accompanied by the abbreviation Rk or Rky—but not always. Here’s a quick summary of the four primary danger categories you’ll want to become familiar with:
Plus sign. Dangerous rocks that lie underwater at all stages of the tide.
Avoid these hazards like the plague.
Plus sign with dots. Dots in all four corners of the plus-sign symbol indicate rocks that are barely visible, or just awash, at MLLW or LAT.
This chart detail shows the symbol for rocks that lie underwater at all stages of the tide.
Asterisk or squiggly-edged, rounded shape, accompanied by underlined number.These rocks cover and uncover with the tide. The symbol is usually accompanied by an underlined number to indicate height above the low-water datum.
If the number doesn’t fit inside the symbol, parentheses enclose the number next to the symbol.
Rocks that cover and uncover. The underlined number gives the height above low-water datum. If no number accompanies the symbol, uncovering information is unknown.
Smooth-edged, rounded shape with number enclosed in shape (or appearing next to it in parentheses). These rocks or islets are always visible. Even at high-tide they stick out of the water, and the numbers indicate their height above the high-water datum.
Rocks shown this way on a chart are always visible. The number is the height of the rock above high-water datum.
Stand-alone Rk abbreviations. Depths accompanied by the abbreviation Rk—with or without a bracket beneath—show rocks covered by that depth at low-water datum. Use caution when navigating close to these areas.
Undersea currents and surface waves and swells constantly shift many wreck positions.
Cartographers can only plot the original reported position of a wreck. Some wreck symbols indicate danger to mariners, while others are safe to pass over.
Dangerous wrecks include half hulls and fish bones surrounded by a dotted circle.
Stand-alone Wk abbreviations, circled or bracketed. The abbreviation Wk is shown along with the known or least-known depth. It’s best to avoid this obstruction altogether if it’s enclosed by any type of circle.
Half-hull symbols. Avoid these dangerous wrecks at all costs. Part of the hull is always visible. At high tide, however, only the top of the mast, cabin, or gunwale might show above the water.
“Fishbone” symbols enclosed by dotted circles. Stay away from these wrecks. Uncertain depths cover the hulk during all tidal stages. When accompanied by the word Masts, some portion of a mast or masts—but not the hull or superstructure— is visible above chart datum.
“Fishbone” symbols without dotted circles. This is the one and only wreck symbol safe to lay your course across and is usually found in deep water.Chartmakers plot these for the benefit of commercial fishermen (whose nets might snag) or to warn larger ships not to anchor near such foul ground.
Stakes, spoils, beds, traps, nets, stumps, posts, and piles provide the sailor with the same challenges as a slalom racecourse. Hazards such as underwater pillings deadheads (floating logs or trees), and submerged stumps plot as small enclosed circles. Circles with dotted boundaries and numbers inside
show the least depth over the obstruction at all tidal stages. The abbreviation Obstn complements many smaller obstructions.
Fish stakes, traps, or nets. Dashed magenta (light purple) lines mark the boundaries of fish-stake or fish-trap areas. These wooden stakes with underwater nets strung between them proliferate in areas such as the Chesapeake Bay, where fishermen use them for catching bait fish. Sometimes you’ll find the words Fish Traps within the boundary lines. More often, however, you’ll see the warning.
See Note,which is an indication to look at one of the descriptive blocks of text on your chart.
Be extra cautious when sailing at night near fish-trap areas; they’re unlighted!
Spoils, dumping grounds, and fish havens. Inland and coastal charts often show circular or square areas of blue water with no soundings.
Ever wonder where old cars, boats, ships, dredge material, and excess garbage end up? These spoil areas or dumping grounds are subject to changing depths, so surveyors rarely bother trying to keep them updated with soundings.
Surrounding you’ll find the words Least depth__ft printed over the middle of such an area, but don’t trust it. Stay clear and go around—not aground.
It’s always a good idea to avoid any charted area showing sparse, widely spaced, or missing soundings. You never know what underwater monsters lurk there, just waiting to ruin your perfect underway day.