The single shoalest point over a feature, the figure a mariner must clear. Finding it takes dense data over the top: multibeam passes straight over the feature at reduced speed, or diver and lead-line checks on masts and piles that sonar can miss. Charted wrecks and obstructions carry the least depth as their value, so an incomplete development can leave a dangerously optimistic number on the chart.
Least depth on the wreck is 6.8 off the bow davit, three passes and the diver agrees.
On wrecks the least depth often sits on a mast, davit or winch that only a beam or two catch; a diver or lead line on the shoalest point settles it.
Also heard as
- shoalest depth
- minimum depth
Related terms
Wreck
The remains of a sunken vessel, charted as a hazard or a feature depending on its depth and size.
Obstruction
A submerged object that hinders vessels or fishing and is not a wreck or natural rock, such as piles or debris.
Development
Extra survey work over a feature or shoal to pin down its least depth, shape and extent.
Feature detection
The ability of a survey system to find seabed objects of a stated minimum size, usually given as a cube edge length.
Shoal-biased
Favouring the shallower value whenever depths are generalised, so a chart never shows more water than exists.