Reading Depths From the Chart Before You Go

The worst habit before a trip is trusting "I know the spot" instead of opening the chart and reading its depths. A nautical chart is not decoration; it is a contract with the water that tells you where you may run, where you may set gear, and where you must stop. Ten minutes reading it saves you hours.

How to read the figures and symbols

Scattered numbers on a chart are depths, either in metres or in fathoms (1 fathom = about 1.8 m), so always confirm the unit printed in the corner before you make any decision. A small figure below the horizontal line is a drying depth at chart datum; a figure above the line shows depth at high water. Contour lines (isobaths) connect points of equal depth and reveal bottom shape: close spacing means a steep drop, wide spacing means flat ground. Light blue marks shallow water, darker blue marks deeper. Most critical are the hazard symbols: submerged rocks, wrecks, obstructions and reefs are your red line. The 5, 10 and 20 metre contours are your practical gates before choosing any route.

From chart to sailing line and fishing mark

• Draw your track so it clears safe depth at low tide, not just at the start of the run.
• Pick a fishing mark at a depth suited to your target species, not simply the deepest hole.
• Record alternate marks for every leg in case wind or current shifts.
• Keep a safety margin of at least twice your draft near islands and reefs.

The chart gives you the general shape; your log gives it experience. Every time you catch and observe, go back and annotate the mark on paper or in your catch log.

Tide, datum, and paper versus digital

Chart depths are normally referenced to lowest astronomical tide, which works in your favour, but an old chart or one using fathoms changes the picture fast. Before every trip compare your mark with the tide table: if you are heading out at low water and your mark sits on a shallow edge, slow down and stand off. Rule of thumb: plan on the shallowest depth along the whole track, not one convenient number.

On paper versus digital: paper never loses signal or battery, while digital updates faster and links your coordinates instantly. The practical answer: digital as primary reference, paper as backup in the drawer, with the edition date written in pen on the cover. B7R gives you tide tables for Shuwaikh and Shuaiba ports, sea state, a fish guide, a catch log, seasons, navigation tools and an SOS emergency button — free on Google Play. Use it alongside the chart, never instead of it.

Common mistakes and pre-departure checklist

• Relying on an outdated chart for an area that has since been surveyed.
• Ignoring the depth unit and mixing metres with fathoms.
• Approaching islands at low tide without checking the tide table.
• Assuming light colour means open water when it usually signals shoal or sand.

Before you start the engine: confirm the unit, fix your track and mark, check the tide table for your hours afloat, log escape marks, scan hazards along the entire route, and carry a paper backup. Prepare with the B7R app before you go: B7R on Google Play.