How to read a nautical chart

Before any symbol, read the colour. It tells you the depth at a glance.

The scattered numbers are soundings: the depth of the water at that spot, measured down from chart datum.

The trap is units. Some charts are in feet, some in fathoms, some in metres. A chart in fathoms showing 6 means 36 feet, not 6. The unit is in the chart title block or legend, and on the NOAA viewer you can usually set it yourself. Check it once before you trust a single number.

An underlined number

Not a depth. A drying height: how far that spot sticks up at low water.

A number in brackets

Near a bridge or cable, that is clearance overhead, not depth below.

The one rule worth memorising is red right returning. Coming in from the sea, red markers sit on your starboard side and green on your port.

The letters next to a lit marker describe its light, and they look worse than they are. Read them left to right as pattern, then colour, then how long the whole cycle takes.

R, G, W, Y

The colour of the light.

4s

The whole cycle takes 4 seconds, then repeats.

Bell, Gong, Whis

It makes that sound, usually driven by the swell.

RACON

A radar beacon. It answers your radar with a coded mark.

So Fl R 4s on marker 2 is a red buoy, number 2, flashing red once every four seconds. In the dark you count the seconds to tell one marker from another.

Hazards are drawn small and are easy to skim past.

Charts are updated, but the sea floor moves and storms rearrange things. A chart is the best available record, not a guarantee.

This is the part most people skip, and it is the most useful part of a chart for an angler. The small letters next to soundings describe what the bottom is made of.

A stretch of M with a patch of Sh or Rk in the middle of it is structure. Bait holds on the edge and predators sit off it. On the Gulf Coast an Oys note is worth a look almost anywhere, and hard bottom surrounded by soft bottom is the kind of thing people keep to themselves.

Once the symbols stop being noise, a chart turns into a map of edges, and fish live on edges.

Bunched contour lines

A drop-off. The faster the depth changes, the more it concentrates fish.

A channel edge

Moving water alongside a depth change, with bait pushed along it on the tide.

The green areas

Flats that drain. Fish push up on the flood and fall back to the nearest deeper water on the ebb, so the drain is the ambush point.

Hard bottom in soft country

Rk, Co, Sh or Oys surrounded by S or M.

Wrecks and foul ground

Vertical structure, often the only hard cover for miles offshore.

Spoil areas

Dredged material dumped in mounds. Lumps that hold fish, usually marked as spoil.

Work out the tide direction first, then find where moving water meets a change in depth or bottom. That is the short version of fishing a chart.

The chart on our guide pages is the official NOAA electronic chart, pulled live. It is there to help you understand the water you are about to fish.

It is not for navigation. Use proper up to date charts and a working plotter for that, and carry paper. Electronics fail at the worst moment, and a chart on a phone in a wet pocket is not a plan.

If you want the complete symbol dictionary, the official one is NOAA's U.S. Chart No. 1. It covers every symbol on every US chart, and it is free.

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