Missing information
On paper or electronic navigation charts, certain areas are marked with the words "Non-hydrographic area" , "Unsurveyed area" or "Incompletely hydrographed area" , "Inadequately surveyed area" . In these areas, delimited on the charts by a continuous or broken line, black or pink, the knowledge of depths is insufficient and it is necessary to redouble vigilance.
Get an idea of the dangers
When navigating in such a zone, the boater must ensure that he or she can navigate safely, taking into account the draught of the boat and its capabilities.
Aerial and satellite views can be very helpful in estimating water depths and guessing the path to take when information is lacking, especially in coastal areas. Seen from above, the non-flush elements that make up the coastline are much more visible than with the naked eye, from the deck of a boat. The shelf, the reefs, a barrier or coral spats that would not be visible from a few meters away become clearly identifiable, and it is then possible to avoid the dangers.
Find out about the nature of the funds
Images can also be very useful when it comes to choosing a mooring area: aerial and satellite views can provide information on the composition of the seabed, to decide where to drop anchor.
To disembark on land in a complicated area, the equipped yachtsman can also use a drone launched from the boat at anchor, to take pictures and make a preliminary identification of the passage to follow.
Accurately assess your position
To use aerial views effectively in navigation, the ideal is to be able to identify the position of your boat and follow its evolution on the image with precision.
Tools such as Google Earth, Geoportal, Google Maps or HERE WeGo allow this, provided they are consulted via a device equipped with an activated GPS. This is especially the case when used on a smartphone, with the corresponding mobile applications.
The satellite views can then be easily taken along on a trip! The consultation works offline, provided that you have previously visualized the area or downloaded the data, connected to the Internet.
A tool that has its limits
The use of aerial and satellite views in navigation is of course not infallible. The images offered are not always recent, and it may happen that changes have been made to the location. In an area with a large tidal range, it is also not possible to know what the conditions were when the photograph was taken. These devices also do not provide information on marine signage.
The use of aerial views is therefore never a substitute for a very careful visual check by the crew. When you have to navigate in a poorly charted area, it is preferable to arrive at a time of day when visibility is good: the bottom is often more visible in the morning, when the weather is clear and the sun is already high in the sky. The reflections are often more annoying at the end of the day.
