Inaccurately charted waters are being surveyed by a superyacht crew who have identified many anomalies when using electronic chart plotters with software based on (very) old surveys

There have been plenty of instances in recent years when
superyachts have found the bottom even when their chart plotters tells them
they have sailed a ‘safe’ course round an obstruction. It’s happened a fair bit
in the Caribbean where surveys are old, yachts are getting deeper and the
demands of racing require accurate depths.

Some anomalies are obvious and there are places in St Barths
for instance where the chart plotter track will tell you that you have sailed
one side of an uncovered rock when you have just witnessed using Mark 1 eyeball
that you have clearly sailed the other side. Frightening!

Equally yachts have sailed in deep water which the chart
plotter has suggested would be far too shallow for a given yacht. For the
racing yacht that’s a particularly interesting scenario.

These anomalies are of particular concern to large sailing
yachts which draw anything from 5m
to 10m. In an attempt to identify some of 
anomalies which exist on charts simply because the surveys are old and
inaccurate, the crew of Sojana are trying to put some time aside to undertake
simple surveys the results of which they will pass on to the publishers of
Imray Iolaire portfolio which Sojana’s skipper Marc Fitzgerald considers to be
the best for navigating in the Caribbean.

They plan to visit known problem areas by rib and measure
depths using a tape measure for real accuracy rather than rely solely on an
echo sounder.