Comparing “Aqua Map Master” and “Navionics Sonar Charts” while Navigating the ICW Between Charleston and McCellanville, SC

19 Apr

This section of the ICW is called the “South of McClellanville” section. It is one of the longest and shallowest trouble spots on the ICW. The following is an overview of this stretch of the ICW between Awendaw Creek and Jeremy Creek.  While there are some places with 8-10 feet of water, there are also stretches with less than 5 feet of water at MLLW. If you drift out of the “channel” you will find water less than 3 feet.  So, what defines the channel?  How do you find it?

We transited this section for the eleventh time on March 31,2019.  We are using 4 navigation products. We have NOAA charts on Coastal Explorer as our primary navigation system, a Navionics chart chip in our chart plotter, and two iPad navigation apps, Navionics and Aqua Map. The NOAA chart 11518 is of almost no help through here: it lacks any depths and does not indicate the edge of the channel.  It can’t: the channel has shifted since last NOAA surveys. You will however, have almost seven feet of tide here, so if you draw more than 4.5 feet  you should wait for a rising tide before entering this piece of water. This stretch will require that you have a bit of tidal help.

The attached screen shots show our track through this 4-mile stretch.  We chose our track through here using the NSC chart.  Having been an NSC user for several years on the ICW and beyond, and having used NSC through here on previous trips, I  had confidence in the NSC app in the shallowest sections.   At the end, the track we followed was pretty much where the US Army Corps of Engineers (USACE) survey would have had us travel.

The following are screen shots off our two iPads. If you are using Sonar Charts (or any charts!) update them regularly. These sonar charts were updated 48 hours before we went through  here.  Aqua Map uses NOAA charts and the charted depths are therefor less detailed and often years out of date. However, Aqua Map Master overlays the USACE surveys onto the NOAA charts which provides excellent detail of the USACE surveyed depths, which in the ICW do not agree with NOAA at all.

AMM with recent USACE data gives a feeling of security, whereas crowd sourced data might be questioned: how long since there were new data tracks added to the charts?  AMM USACE surveys gives you a narrow path to follow.  The Aqua Map NOAA chart does not provide any help for the water depth outside the surveyed path.  AMM only surveys the depths along the center of the ICW. NSC gives a better “picture” of the channel edges. NSC gives you a wider path and the confidence to stray off the USACE survey to find adequate water depth.

WE traveled 800 miles in the ICW using both navigation apps. Where NSC and AMM share coverage through this section of the ICW, they appear to be equally accurate. Either one will help  you navigate the ICW. Ideally, I’d have both navigation apps to transit the ICW.  If I could have just one of these two apps I would stick with NSC. NSC covers the ICW and all the rest of the waterways in the US and Canada.

NSC: The white/blue line is user defined. On these charts the white area is over 5’ deep, the blue is less than 5’ deep.  The red stippled areas are 4’ or less.

1A NOAA 11518 Showing this 4 mile section. No helpful details at all.

1B Navionics Sonar Chart

1C Aqua Map Master. The colored channel is the USACE survey.

2A NOAA chart from  R38  and north 0.5 miles. There is no helpful information to pick a track through here.

2B NSC from  R38  and north 0.5 miles. Notice our track follows the deepest water indicated in the NSC crowd sourced depth data

2B AMM track.  The USACE survey is a narrow  channel.  Note where the track is at the edge of the survey.  NSC indicates there is still some good water outside the survey limits.


3A Navionics G39 to R38

3B AMM G39 to R38

4A          Navionics through R40 shallows.  This is the worst section

4A          AMM through the R40 shallows.  You can clearly see the white area which the NOAA chart indicates as the north edge of the channel, which quite clearly has completely silted in..

5A          NSC G39 to R38 gives a better picture of the entire channel width.

5B          AMM G39 to R38  The USACE survey does not pick up the deep water just past the bend north of G39.


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