Creating Your Own Bathymetry

Buying bathymetric charts can expand your knowledge of the undersea world, but creating your own bathymetry can expand it even more. 

Modern digital charts are nothing short of amazing. They display contours down to one foot, cover just about every body of water in and around the nation right down to large mudpuddles, and provide you with the ability to customize the data they deliver and how it’s presented on the screen of your MFD. There’s no doubt that arming yourself with the best bathymetrics will help you catch more fish, but there is one fly in the ointment: errors in the data pool. 

Read Next: Kiss Your Generator Goodbye

Why Make Bathymetric Charts? 

While on the whole most of the mapping out there is shockingly accurate, it isn’t always 100-percent on target. This can be the result of an error in the original data (stock NOAA soundings are incorporated in many cases), a problem encountered during more recent surveys, or natural changes like shifting sandbars and channels cut by storms. You could go for years without even noticing flaws like these and think it’s not a big deal. But when you run 40 miles to get to an underwater pinnacle that rises to 800 feet from 1200 feet of water and discover it’s nonexistent, you’ll be more than a little bit upset. And at that point, all you can do is curse the guy who went to get a fresh cup of coffee and missed it when the survey gear pinged a whale. 

There is, however, a way you can enjoy the latest and most accurate bathymetry possible: create it yourself. 

If you have Navionics on your phone and a MFD with WiFi, you can even information-share and take your self-gathered data home with you. 

How to Make Your Own Bathymetric Charts 

The good news is, once you have your system all set up and ready to roll creating your own bathymetric charts is more or less set-it-and-forget-it easy. The bad news is that you’ll have to tell your machine to start paying attention to the pings from the sounder and GPS position data at the same time, and to record all that data. 

The exact setup for different systems varies by manufacturer, but none are terribly mind-boggling. Let’s use Garmin for an example. You’ll have to open up the menu, select “Quickdraw Contours,” then select “start recording.” A circle will pop up around your boat showing you the area of coverage as you move along. It’ll be green if the readings are all good (yellow or red if not). Garmin says a two-GB memory card gets you about 1500 hours of data recording, and that you should get good data when travelling at up to about 10 mph of speed assuming you have a reliable transducer installation and there aren’t other mitigating factors. 

You can watch as new bathymetric appear in real time, on Raymarine’s RealBathy system. 

Or, consider Raymarine. On an Axiom you choose the “cartography” setting, open “depths,” select the offset distance for your transducer depth, choose the reader slot with a memory card, then hit “record depth data.” If you hit the “RealBathy” button, it’ll start showing the bathymetrics in real time. You can also adjust the transparency level (“visibility”) to less than 100-percent, to see the charted bathymetrics at the same time. 

All of the major players have some sort of similar system, but naturally, they aren’t all created equally. Furuno’s Personal Bathymetric Generator (PBG) for NavNet TZtouch3 is probably the best example of a system that takes things to the next level. With the DFF3D transducer and 120-degrees of beamwidth you can cover large swaths of water at one time, and the area of width will be about twice the depth. Tide compensation calculations take place right inside the Furuno’s brain so you don’t have to think about offsetting for tidal swings, and the 256 GB of storage that comes with the unit holds enough data for “a lifetime” of PBG. 

Stock contour lines get a huge boost from Furuno’s PBG with DFF3D, and this area — about the size of 250 football fields — was covered in just over 20 minutes. 

Downsides to Making Your Own Bathymetric Charts 

The big downside to making your own bathymetrics is the time investment. Getting the system up and running will be easy, but if you want to thoroughly cover any one area, you’ll basically have to do a methodical survey sweeping back and forth across it as the MFD collects data. In some cases this will make sense (say, a large local hotspot with lots of depth variation that you fish on a regular basis), but in others it wouldn’t be worthwhile.  

What many anglers will find useful, however, is doing a sort of long-term survey of their regular fishing grounds. Start the system up and the beginning of each trip, and then ignore it. By the end of the season you’ll have thorough coverage in some areas, partial but potentially interesting coverage in others, and spotty coverage that might show something here and there in the spots you only hit once or twice. In any case you’re bound to find something new — a hump that doesn’t show up on any of the purchased charts, or an underwater point that’s 50 yards from where it belongs. And in all likelihood you’ll see a few places with partial coverage that are worth a second look. 

Note that some systems have one level of internal storage or another, and others require the use of a chart card. Pull the card out of the machine, and in this case the data goes with it. Also remember that we all make mistakes, and just because you collect the bathymetrics doesn’t mean you won’t get fooled by a whale of your own, nor that the next big storm won’t turn your accurate readings into ancient history. Still, any way you cut it, the ability to create your own bathymetrics is utterly awesome, and just about anyone out there with a modern MFD has the ability to do it. Harness this tech, and you can become a more effective angler. 

Lenny Rudow …has been a writer and editor in the marine field for over two decades, and has authored seven books. He is currently the Angler in Chief at Rudow's FishTalk Magazine, is Electronics and Fishing Editor for BoatUS Magazine, and is a contributing editor to several other publications. His...