Checking keel clearance, charted depth against draught

Checking charted depth against draught is simple:

charted depth minus draught gives your keel clearance; below half a metre it becomes critical.

Charted depths are measured from chart datum, which in tidal waters is mean low water springs, so there is usually more water there than shown, though now and again there is less. On inland waters the level rises and falls with rain and wind, and in river estuaries shifting sediment adds to that.

Half a metre of keel clearance is the lower limit for calm water. In waves the keel dips deeper still, and in a persistent offshore wind the level drops measurably below the charted figure.

Grounding is the most frequently reported cause of claims. It is usually a matter for comprehensive hull cover; check whether consequential damage to rudder, shaft and gearbox is included and whether the craning needed for an inspection is paid where damage is suspected.

Worked out for your type of boat

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