Navionics Sonar Charts (NSC) have proven to be an invaluable tool for cruisers. NOAA charts are the basis for all American charts. They are invaluable: NOAA has very limited budget for surveying the ICW. The NSC adds crowd sourced charts are built on the NOAA charts with the addition of bathymetry supplied by cruisers. NSC are crowd sourced surveys. The NSC charts are finely detailed. The details can make it difficult to actually tell which depth contour you are crossing; is this the 8-foot contour, or the 12’ contour? Here is the New River ICW Inlet crossing NSC with the “depth shading” the blue area set at 6’. There are lots of contour lines. But what do they stand for?
The USACE surveys available in Aqua Map Master (AMM) are an essential tool for transiting those areas where the Corps recorded depth surveys. The AMM/USACE surveys are color coded and very easy to read. This is the AMM chart with a route created in NSC and transferred to AMM. With the USACE color coded surveys it is very easy to pick out the deeper/deepest water. In the screenshot below is a route I created in Navionics and then transferred to Aqua Map Master.
To make the NSC easier to follow I wanted to add colors. If I was going to add color I decided, to the extent possible, to mimic the corlors and ranges in the USACE surveys.
Tap the MENU button. Tap the MAP OPTIONS button. then scroll down to “Shallow Areas”, “Depth Shading” and Fishing Ranges”. I used the “fishing ranges” to add color. Here is the colorized NSC chart with the original route I created.
How to do it? First, I set the “shallow area” at 4 feet. That gives you the red stippled area. We draw 4.25’ so if we see the red stipple, we know we cannot go there at MLLW!
Next add a red fishing range for 5 &6 feet. Note NSC still differentiates the contour lines with in this red band, by shading the reds.
Next, add orange(s) for 7 & 8 feet.
Next at teal(s) for 9 & 10 feet.
Next add deep blue(s) for 11 to 14’.
When you are in areas covered in a USACE survey, you will often find the NSC charts generally agree. Not always, but I find that when the two systems disagree, it means I should take some time and do further research. If the USACE survey is less than 6-month s old I give it more weight. If it is over a year old, I give NSC more weight. Neither system has a perfect record!
Once you are off the ICW there are very few USACE surveys. Barnegat NJ, inlet is one example. Here is the NOAA chart, updated in mid-August 2019.
Here is the NSC chart of the same time frame. Not only does the NSC chart have the depths in the inlet, it also has numerous ATONs not shown on the NOAA Chart!
Which chart would you prefer to use if you are entering this inlet? NSC charts cover hundreds of thousands of square miles of US territorial waters, not covered by USACE surveys. Adding the colored fishing ranges makes the NSC charts easier to read and it facilitates comparing the two chart systems to find the best route forward.
It is important to note, that there are no charts which are perfect. There are no charts whose bathymetry is always precise to within a foot of depth. Maybe they were perfect on the day the data was recorded but as time goes by the sediments can and will move. With any charts, as you move into shallow water, you should slow down and watch your depth finder. The USACE surveys and Navionics Sonar Charts are two very handy tools to have in your navigation kit and at your helm.