News & Events for Chesapeake Bay
Navigation Options: Who Do You Trust?
Date Posted: 2018-10-24
Source: Bob Sherer, Waterway Guide Contributor
Editor’s Note: Robert Sherer, aka. Bob423, and his wife Ann have made the round trip from New York to Key West on my 42 ft sailboat eight times. He is currently on his ninth trip down the AICW to Key West. Sherer is a paid on-the-water Cruising Editor for Waterway Guide and also publishes a guidebook. He has collected a list of examples, so you can decide for yourself who to rely on. There’s no simple answer for all situations, but here are his personal observations.
When it comes to bestowing our trust in sources of critical navigational information we must make our way through a sea of advice, opinions and options.
Some say, just follow the Aids to Navigation (ATONs). Others say pay more attention to the chart. Still others have favorites like SonarChart from Navionics. The surveys from USACE are also popular to follow. Then there are the crowd-sourced data from Waterway Guide and other sources. There are also many guidebooks, including my own 2018 ICW Cruising Guide that addresses trouble spots. The choices can be bewildering, there are so many.
For this article my definitions are as follows: A chart can be on a chart plotter, a tablet (e.g., iPad) or on paper, it doesn’t matter as far as accuracy if they are all up to date and viewed at the proper zoom levels. The sources for coastal charts in the US are those provided for free by the National Oceanic and Atmospheric Administration (NOAA). NOAA updates its charts once every seven days, but not every chart is updated, only the ones with changes, perhaps 10% to 15%. Even then, the changes usually affect only small areas of the updated chart. How those updated charts find their way into navigation programs and apps also varies between the providers.
Some navigation apps use the raw charts from NOAA. Either Raster Navigational Charts (RNC) that look like their paper counterparts or Electronic Navigational Charts (ENC). iNavX displays the RNC charts for free once you buy their app. Likewise, SEAiq displays either format for free once the app is bought. Both apps read the raw NOAA chart catalog and, after an update (press a button), your charts will show the same data as NOAA. Charts other than NOAA are available for an additional price from each app. Aqua Map, iNavX and SEAiq also add Waterway Guide icons on top of the charts, which can be tapped to bring up additional information about alerts, marinas, anchorages and other information.
Other navigation apps employ a different approach. Their starting point is also the NOAA database, but their charts are formatted into a seamless whole (quilted) so when you zoom or pan, there’s no hesitation in the screen display as new charts load. Also added to the charts in some cases are Waterway Guide icons, as well as tide and current markers and other crowdsourced data. With the formatting and additional icons added, the cost for the provider is in the additional processing required. As a result, the frequency of updating is not always the same day that the updated NOAA charts are released. In contrast, there is no delay with iNavX or SEAiq, which use the NOAA format directly.
Aqua Map reports that they rebuild their charts directly from the NOAA source every three months and the rebuild is directly from the NOAA standard. Navionics depends upon manual updates to their Navionics+ charts based on changes to the NOAA charts and, in some cases, from other inputs. The changes lag behind NOAA but can be close if all the changes are caught during the manual corrections, which is not always the case.
In a league by itself are the SonarCharts from Navionics. They receive inputs from boaters using chart plotters they partner with that upload soundings to Navionics as they navigate. Navionics takes the uploads and constructs their SonarChart product with 1 ft depth contours. Updates are provided upon clicking (or tapping) on the “Update All” button in their app. Be ready for huge updates, usually in the 300 to 700 MB, which can be even higher if you let the updates go longer than a couple of weeks. The algorithms used by Navionics to create their SonarCharts are not shared so I do not know how they do it, or the weights they may give to different inputs, I can only see the results in the examples that will follow.
US Coast Guard (USCG) ATONs
ATON is short for Aids TO Navigation and are maintained by the US Coast Guard (USCG). Most of the weekly corrections to the NOAA charts are for changing ATON positions or new ATONs. One might think that ATONs would be more accurate than the charts since it’s the charts that are being updated, not the ATONs, which have already been repositioned by the USCG. However, there are many places where there are no ATONs and the charts can be useful for staying centered in a narrow channel or when crossing an area with strong currents. There are also some cases where the ATONs will lead you to shallow water. I would expect that to be eventually corrected but the USCG has a huge workload and can’t always move or add every buoy as needed. I will cover all this in more detail later with examples.
US Army Corps of Engineers (USACE)
Another source of very valuable charts are the soundings taken by USACE districts along the ICW. They have survey boats that navigate the areas of their responsibility and then create a chart with depth resolution to 1 ft. These charts are published and available for everyone to use. The Wilmington USACE surveys the inlets as often as needed, sometimes multiple times a month such as at Shallotte and Lockwoods Folly, and even publish recommended routes through the shallows. It is invaluable information. Waterway Guide includes the most recent soundings in the form of chartlets in the alerts for each area along with a GPX file of the USACE recommended route available for downloading off the Waterway Guide site. The Charleston USACE does a survey of the ICW about once a year, not as often as Wilmington, but still very useful since they cover the Isle of Palms and south of Charleston down to Port Royal. The Savannah and Jacksonville USACEs do not publish graphical ICW surveys, but rather just send a boat down the ICW about once a year and measure the minimum depths in the middle and both edges of the channel through shallow areas, which I do not find very useful.
Crowd Sourced Data
Waterway Guide and Active Captain are the two biggest collectors of crowdsourced observations and reviews. Both can be useful in avoiding shoaling areas as well as general information about marinas, anchoring and other items of interest. Active Captain accepts all inputs as is, but Waterway Guide reviews and verifies the input first before publishing. An input like, “Came through at high tide, no problems” is not particularly informative and we’ve all skipped over such reviews when reading Active Captain posts or while looking for a post by Bob423. In Waterway Guide, paid editors and experienced skippers, often an on-the-water editor like me for portions of the AICW, will research the comment and either contact the person who posted the observation for more information if it’s vague or unclear, or consult with other staff members who administer the Nav Alerts. Actual depth readings, tide levels, depth of keel, etc. are often solicited from the person making the post to make the information more useful. The results are then packaged to appear as guidance in the Waterway Guide Navigation Alerts. Since I maintain the Waterway Guide alerts for especially troublesome portions of the AICW, I naturally look first at the latest information I’ve posted when transiting those areas. I use both the Waterway Guide and Active Captain as sources in deciding the best way to negotiate a shallow area because the advantage of crowdsourced data is the immediacy. It’s the “happening right now” that can be important, and the observations can be in advance of NOAA or ATONs position updates and even USACE surveys.
How to Proceed
Now to the more interesting part of this assessment. In the spring of 2018, I accumulated examples where one or the other type of information was more useful, less useful, or just plain wrong. I would think we would all be interested in a decision that a captain would have to make if he or she were following only charts, ATONs, USACE, or crowdsourced data. So, you are the decision maker, you’re the captain – what will you do?
Example 1: Lockwoods Folly Inlet, ICW Crossing
Below is the NOAA chart for Lockwoods Folly downloaded directly from the NOAA server. As you approach the Lockwoods Folly inlet, the ATONs do not match the chart. How would you proceed? Take a minute and think about that. For example, how do you negotiate R46A? I’ll summarize my approach at the end of the example.
For example, how do you negotiate R46A? I’ll summarize my approach at the end of the example.
Now let’s look at what the area really looks like. Below is the USACE survey of 9/28/2018. It shows the current positions of all the ATONs and the depths with 1 ft contours.
When heading south, you enter the chart from the right. If your preference is to just follow the ATONs, then you have to decide when to leave the channel to honor G47. If you wait too long, you’ll see 5 MLW at best and perhaps even 4 MLW. When passing G47A, you can’t hug it, you have to know how far off to be when you go by. Assuming you’re successful in passing G47A and honor R48, then you have to decide when to turn to starboard once past R48. If you turn too soon (hug R48) you’ll find shoal water, if you wait too long, you’ll also find shoal water.
I think you would agree that having a USACE chart is a pretty valuable asset for areas like Lockwoods Folly Inlet. Not only does it show the depths, but also the updated ATONs. Even more valuable would be having a GPX route loaded in your chart plotter or tablet. More on that later. While we’re looking at a variety of sources for help, let’s look at SonarChart from Navionics.
Here’s the SonarChart of 10/19/2018 for Lockwoods Folly.
The depth contours do not match the USACE chart and the ATONs are not represented correctly. R46A does not exist at Lockwoods Folly but it is still shown on the chart. G47 is shown as missing and also present but in the wrong position. How would you proceed just looking at the SonarChart? How would you resolve the G47/R46A discrepancy? Should you pass R46A to starboard or honor G47 to port? At any rate, it’s a confusing picture. It’s a good thing we have the USACE survey!
Having looked at USACE, NOAA, and SonarChart, where does crowdsourced data come into play? From Waterway Guide you would learn that as of 10/18/2018, R46B is up on land! It’s not there to guide you. Crowdsourced data on Waterway Guide gives you a chartlet of the USACE survey showing the alternate route from Hank Pomeranz and a GPX route to download to follow. It gives much more leeway than the USACE route to stay away from 1 to 3 ft depths as the strong currents push you around. Now you don’t care if R46B is up on land, you have a route to follow on your chartplotter. The chartlet is also available through Aqua Map and iNavX as part of the daily download of alerts. It’s available after the download, you don’t need an internet connection once you download the updates to see the chartlet. If you plan ahead, you can download the GPX routes in advance when you have an internet connection so they are ready for immediate use when you reach the inlet. Active Captain data is not monitored for accuracy so you’re on your own in judging who to believe. Nevertheless, it can be useful if you know the reputation of the poster.
Above is another example, this is the Aqua Map chart for Lockwoods Folly Inlet.
The red line is the Hank Pomeranz recommended route for the deepest water. The ATONs are based on the NOAA chart so their placements are not current, but the route is current as of 10/18/2018. Both the Waterway Guide and Active Captain icons are shown. Tapping (or clicking) on either one will result in a popup with information on the passage as described previously. Although the chart does not show depth detail, it’s easy to follow the GPX route to safely pass through the inlet. With either Aqua Map or iNavX, you will also have the current USACE depth survey chartlet for reference which is useful for buoy placements and a general sense of the path.
My personal strategy for the ICW inlets is to first reference the latest USACE survey, which is available directly from the USACE district for the area of interest (internet required) and read over the latest Waterway Guide posts but look at Active Captain, too.
Let’s devise a rating system for the charts.
- One point for correct placement of ATONs
- One point for correct depths.
For just following the ATONs:
- One point for following the ATONs at low tide but needing some info on the turns to avoid shallows.
- Two points if it’s a straight shot, just honor the ATONs and there’s no chance of a grounding at low tide.
Let’s look at how following the charts or ATONs stack up. Let’s count the points.
NOAA chart = 0. Depths not right, ATONs not right.
Follow the ATONs = 1. You can sort of follow them, but you have to realize that what you see ahead of you does not match the NOAA chart and you have to know how and when to round the turns.
USACE survey chart = 2. Perfect, who could ask for more? Depths are right, the ATONs are in the right spots and a route is included or one can be generated.
SonarChart = 1. All the ATONs are not all placed correctly and that could confuse your navigation. Additionally, more depth is shown than actually exists which could lead you to try passing through the inlet when there’s not enough water per the USACE chart and going aground. It would really help to reference the Waterway Guide data, so you’re not surprised by the ATONs. Active Captain may also have useful comments if it’s kept up to date.
Crowd Sourced Data = 2. From the crowd-sourced data from Waterway Guide. you would know that ATONs do not match your charts and even get general guidance on a route referenced off the new ATON positions. From the Waterway Guide icon in either iNavX or Aqua Map, you would also get the USACE chartlet (no internet required). With Aqua Map, you would also get a link to download the GPX route (internet required). From The Waterway Guide you would also know that R46B is off station and up on land! Active Captain may help too if the hazard is kept up to date.
Winner! Tie between crowdsourced data and USACE survey chart.
Example 2: Altamaha Sound by R208 in Georgia
Below is the NOAA chart of the area, 11508 with the last correction on 4/4/2018 but cleared through 8/25/2018. Note the ICW path from R206 to R208 to G209 and finally to G211. Looking at the chart, how would you proceed?
On some charts, the magenta line passes right over the top of the 2 MLW spot. Are you one who follows the ATONs first and foremost or do you pay more attention to the charted depths? In the last two years, I’ve not passed this spot close to low tide without seeing at least one and, sometimes two, boats aground by R208, about where the 2 MLW spot is located on the chart! So, what would you do?
Let’s see if SonarChart helps here.
It pretty much agrees with the NOAA chart. Both charts have the ATONs in the right locations and the correct depths are shown around R208. However, if you like to just follow the ATONs, you will have company with others doing the same thing as you wait for high tide after grounding.
How about crowdsourced data? Waterway Guide will warn you to stand off R208 and provides a chartlet (shown below) from Aqua Map showing the correct route. Active Captain will give a text description of how to proceed.
NOAA = 2. Accurate depths, accurate ATONs.
Follow the ATONs = 0. Unless you draw less than 2 ft when passing through at low tide.
USACE survey chart = N/A, doesn’t exist for this area
SonarChart = 2. ATONs and depths all good.
Crowd Sourced Data = 2. Read either Waterway Guide and Active Captain and you’ll be good through here.
Winner! Tie between NOAA, SonarChart and Crowdsourced Data. The real loser is just following the ATONs.
Example 3: Dawho River, South Carolina. East entrance.
Below is the NOAA chart for the east entrance to Dawho River in South Carolina dated 5/18/2018 but cleared through LNM 31218 (8/7/2018) and NM 3418 (8/25/2018).
With only the NOAA chart to go by, how would you proceed at low tide? There’s a troubling 3 ft spot that seems to be directly in a line from R108 and G111. Complicating the plan is that G109 is not shown although you will see it when attempting a passage (between G111 and R108).
This is one of those places where we do have a survey from Charleston USACE although it’s dated 9/27/2018. Let’s take a look.
The marked channel looks a little scary, just look at the measured depths at low tide (if you follow the chart and ATONs).
Let’s see if SonarChart helps here.
It looks like you could deviate off the channel between G109 and G111 (kudos to SonarChart for showing G109!) and maybe find 6 MLW. It gets pretty narrow close to G115, which you want to pass well north of. You would have to choose between following the channel per the NOAA chart or trusting SonarChart, especially since it looks like you want to pass G111 on the wrong side for the best water.
Let’s look at the Charleston USACE chart again but this time with a new route plotted, taking advantage of the soundings by USACE.
With knowledge from the Charleston USACE, I’ve plotted a new route for 8 MLW that bypasses all the shallow spots of the official channel. This route has been confirmed by at least five boaters including myself in the spring of 2018. How does that route appear on Aqua Map (and therefore on the NOAA chart?), see below.
The red line is the route based on the USACE survey and the dotted line is my path 5/2/2018 for 8 MLW. Without knowing the background, what would you think about taking this path when the NOAA chart and SonarChart shows you headed for depths of less than 2 MLW? And yet, at least a half dozen captains have taken the route and reported the same depths. You can see all the scattered comments from Active Captain users. There are two for Waterway Guide, one is my guidance with a chartlet of the USACE survey and a GPX file for downloading. The other Waterway Guide marker is to show the location of G109.
On to grading:
NOAA = 0. Depths are not accurate, and an ATON is missing (G109)
Follow the ATONs = 1. This is a maybe if at low tide, depending on your draft. You would be passing over a 3 ft MLW spot if you honor the ATONs and stay in the channel.
USACE survey chart = 1. The depths are correct, and it shows the way to a deep-water route but none of the ATONs are shown.
SonarChart = 1. ATONs are good but the depths are not accurate for the 8 MLW route area. One could argue that it’s good enough to get through at MLW but the depths in the channel disagree with the USACE survey depths even there. Having been through there myself multiple times, I never saw a 6 MLW path following the ATONs or the charted channel.
Crowd Sourced Data = 2. Read Waterway Guide (chartlet and GPX route) and you’ll be good through here. Active Captain will also help here since I entered the deep-water path myself.
Winner! Crowd Sourced Data. Both Waterway Guide and Active Captain have the new route for 8 MLW (I posted in both) but Waterway Guide also has a chartlet showing the route and a link for downloading it along with the GPX route for 8 MLW.
A dredge was to pass through this area as of 10/21/2018, so the charted channel may be good now, we don’t know yet. It will be interesting to see what they do here. Maybe we can just go back to honoring the ATONs. Again, you will want to monitor Waterway Guide for the latest information on this passage. Active Captain may be helpful too. Aqua Map has both sources available on their charts.
What have we learned?
I have picked real-life examples of where just following one source or the other can lead you astray. The exception is the crowdsourced data. Since it’s updated by on-the-spot cruisers, it’s valuable information and should be read before embarking on your cruise for the day. The one source I highly recommend is the USACE surveys out of Wilmington. They are committed to surveying inlets as many times as required to provide a safe path for us boaters. SonarChart is also a good source, but it takes time for contour updates in rapidly changing areas like inlets where the USACE surveys can’t be beat. In more stable areas of the ICW, which is at least 95% of the route, it’s a good tool. Most of the ICW doesn’t change all that much and the NOAA charts have mostly caught up with correct depth contours where there’s a level of stability and mostly can be depended upon for 90% or so of the route.
I could go on and on with examples of where one specific source is better or worse than another, but I think you get the picture. I’ll cut to the chase. In brief, don’t depend on only one source, here’s my preference:
Priority One: Use the USACE surveys if they are current as the number one priority and the GPX routes based on their waypoints. I post many of them in Waterway Guide.
Priority Two: Use the crowdsourced data, be it either Waterway Guide or with less detail, Active Captain. There is no substitute for on-the-water reporting. I have a bias towards Waterway Guide since I personally maintain the alerts, but I also input some information into Active Captain as I go south.
Priority Three (tie): Use SonarChart, it’s good for 95% of the ICW. Check it against priority one and two items to be sure it’s telling you the right path to follow and for ATON placements. The great limitation of SonarChart is the non-support for importing and exporting routes unless you do it through one of their partner chart plotters. Also crippling is their non-support of Waterway Guide or Active Captain, it is not a stand-alone app.
Priority Three (tie): Use a charting app or program that accepts GPX inputs such as Aqua Map. The advantage of Aqua Map is the display of both Waterway Guide and Active Captain data, so you can see both sets of advice without changing apps. It will accept GPX routes directly without additional steps and display them ready for navigation, so it makes using the USACE GPX routes I provide easy to use.
I ranked a tie between SonarChart and Aqua Map since they complement each other. Each has capabilities the other does not. Keep in mind that iNavX and SEAiq are other options and will always be up to date with NOAA charts upon hitting the update button. Aqua Map does a complete update every three months. Whether you prefer the user interface and ease of operation of iNavX, SEAiq or Aqua Map depends upon your personal preferences. They will all accept downloading of GPX routes.
Here are the links and references I’ve used in this article:
Wilmington USACE surveys for the ICW from North Landing River to Little River
Wilmington USACE surveys for just the inlet crossings
Charleston USACE surveys
NOAA Nautical Chart Catalog and Chart Viewer
Aqua Map Marine app for iPad and iPhone (also available on Android) has Active Captain and Waterway Guide
Navionics USA HD No Active Captain, no Waterway Guide, no importing of routes but it has SonarChart.
iNavX Waterway Guide
SEAiq USA Waterway Guide
2018 ICW Cruising Guide by Bob423, the fourth edition, highlighting all the shallow areas and the best path through them as well as what we’ve learned in eight years of New York to Key West annual round tips.
Facebook group on ICW cruising and Aqua Map use
Daily blog on cruising the ICW starting 9/15