Navionics Sonar Charts

29 Aug

As you have no doubt noticed, the cartography I use in most of my posts is by Navionics. We navigate with Coastal Explorer on our PCs and use a Navionics + chip in our chart plotter and a Navionics  US & Canada HD app on our iPhones and iPads. With the Navionics + and the Navionics app there are three cartography options.

  • First is a duplicate of the NOAA charts, but with a different color palette chosen by Navionics.
  • Second is the Navionics + charts. They are built on the NOAA charts but with some added features.
    • In app tides and currents
    • Marina identification and contact information
    • Aerial photograph of marine facilities
    • User added content which includes shore side facilities such as grocery stores, nearby restaurants and taverns and marine stores such as West Marine.
  • Third and most important is what Navionics calls Sonar charts. These charts include everything in the Navionics + charts above with crowd sourced bathymetry. This data is collected from Navionics chart chip owners who select agree to collect the data and upload sonar log files each time they update their chart chip.  Navionics has been collecting such data worldwide for about a decade.  Navionics records time. Lat., Lon. and depth.  The data is automatically corrected for state of tide.

After 9 trips on the ICW in the past 4 years, I have the following observations on charts and cartography

  • NOAA does a good job of updating their charts in response to the USCG moving and changing aids to navigation (ATONs ). Our PC navigation updates all charts every time we turn it on. Navionics can be updated anytime you choose, and very often has updates days, weeks and in some cases years ahead of NOAA.  Navionics charts are very easy to update.  I do it almost daily while I’m on the ICW.  They can update over a cell phone connection.
  • Since we started using sonar charts in January 2014 we have watched the Sonar Charts steadily improve. Northbound in 2017 the improvement was startling. We could at times drive the boat following the deeper water shown in the Sonar Charts.  By the time we went south  in 2017 they had improved even more.  The Sonar Charts were very quick to pick up the changes to the  ICW channels  caused by the 2017 hurricanes.
  • Northbound in 2018 we continued to navigate using Coastal Explorer using NOAA Charts. We found we were using Navionics+ in the chart plotter primarily  for the radar overlay, but we were piloting the boat  using the Sonar Charts on an iPad mounted at the helm.
  • In spring of 2018 we also added the Aqua Map app to our devices. It uses NOAA charts, but only updates every 6 months.  However, it is an alternate source of  Active Captain content which we primarily access though Coastal Explorer on our PCs.

Since we moved aboard this boat 9 years ago we have cruised something  on the order of 32,000 nautical miles. We have used a couple of different PC navigation programs and a whole lot of different navigation apps.  Based upon what we have seen in the 10,000+ miles we have done since the fall of 2016 cruising in 12 states and two Canadian provinces, Navionics Sonar Charts is a must have navigation application.

 

Sonar Charts are built on input from a number of sources  including NOAA, USACE, etc., but primarily the data is acquired from boaters. If boaters are not traversing a certain waterway, there will be no data.  This was particularly noticeable in the fall of 2017, southbound after the hurricanes.   In NC, Lockwoods Folly and Shallotte Inlets were dredged in the spring of 2017.  Using USACE  data and the data of  the north bound boaters, Sonar Charts showed both channels were straight and deep.  After the late summer hurricanes, the channels shifted significantly.  Sonar Charts  was up to speed on the new channels in a matter of a few weeks.  Between USACE surveys and  boaters’ sonar logs, the new channels were easy to see.  BUT the charts continued to show the old channels.  There were no boats transiting the old channels because they were filled in,  so the Sonar Charts continued to  show the old channel.

This brings us to a very important point. No matter whose charts you use.  No matter whether you have kept them up to date or not, travelling the ICW you must always pay attention to the established USCG ATONs in the restricted waters of the ICW trouble spots. That is the one essential rule of navigating the ICW. Sonar charts will give you a very good idea of where to go, when travelling in between ATONS. https://www.sailfeed.com/2018/04/little-mud-river-stm-655/

In many large bodies of water such as Long Island sound, The Chesapeake Bay main stem, Albemarle Sound, Pamlico Sound, Lake Champlain,  etc., the NOAA and Sonar Charts are in close agreement.  But when they are not in agreement, the Sonar Charts more closely match what we are seeing on our depth finder.  Are the Sonar Charts perfect?  No, it they’re not.  In our cruising we have yet to find any place, where the  NOAA chart depths are more accurate than the Navionics Sonar Charts.  We have certainly found places where the Sonar Charts did not agree with our depth finder, but in those places the NOAA bathymetry was worse!

So, Sonar Charts are another tool to have in your navigation tool kit.  There will be times when Navionics shows more water that your keel says is present. However, we have been using his app for 4 years, and full time for the past year and a half and we have never touched bottom due to any inaccuracy of the sonar charts.  This s certainly in large part due to the fact that we are very cautious traveling in water where the depth finder says we have less that n 10 feet. Which is not to say  we have not grounded once or twice, but in the most recent round trip to FL we never touched bottom except due to pilot error, and  in a cruise  up the Hudson and into the Canadian lakes we never touched bottom due to an error in the sonar charts.

I’ll leave you with one recent example of  the accuracy of sonar charts. Exiting Plum Gut  and entering Long island sound, there is a large 350-foot-deep hole scoured out by the 2kt currents  flooding into the sound. The bottom very quickly rises to about 100 feet and the NOAA Chart shows the bottom of the sound as a vast smooth plain.  The Sonar Charts show a very corrugated bottom profile with multiple “sand waves”.  Here is a screen shot showing the Sonar Chart and the depth finder as the bottom rises and falls 30 feet.  One might be tempted to ask, “Who cares what is going on on the bottom 100 feet below the boat?”  Well, these waves are constantly moving westward across the sound, much as sand dunes move with the wind.  Sonar Charts is able to locate and monitor these dunes.  The depth finder shows  in detail exactly what the chart  bathymetry indicates. The same technology  demonstrated in this screenshot is exactly  the sort of detail you will see along the ICW.

Plum Gut on NOAA 13209 Most recent update April 2018

Plum Gut showing sand waves in Long Island Sound  Navionics Sonar Chart Updated as of August 21, 2018

 Sonar Chart and Depth Finder

Comments

  1. SAIL the ICW

    Hi Greg. I wish we could bring our boat out to your waters! We have used the Navionics Sonar Charts in Canada through the Rideau Lakes and canals and over to the St. Lawrence, then back up the Chambly River to Lake Champlain. We agree with you. In our experience they are better than the CHS charts in many places.

  2. Greg Branch

    I have found the “sonar charts” more accurate and detailed than the Canadian goverment charts for the inside passage from WA state to Alaska as well along BC’s coastline.

Comments are closed.

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