Navigating with OpenCPN on an Android Tablet

8 May

After well over a year of landlubbing where I could barely even find time to adjust my docklines I’m finally back on my boat! I’m writing this in Ft. Meyers Beach, FL, which we’ve reached in a couple long, busy passages. Unfortunately I couldn’t steal away for long so I’m doing what I hate to do which is sailing on a schedule. This means sailing in any wind that we can get, which in turns means unpredictable passage times. Well I say unpredictable but somehow we always seem to reach our destination at the same hour- 3am. I’m no stranger to night passages, or night entrances and I’m careful about where I will and will not arrive after dark but this trip, for the first time on my boat, I’ve been able to make night entrances with a sense of near-total ease. We even ran the channel into Ft. Meyers in the middle of the night under full sail and I didn’t have a single shaky-legged moment! I have one new gadget to thank for this newfound sense of ease- an Android tablet running OpenCPN and NOAA ENC charts.

As a sailor (and I suppose in general) I’m a cheapskate and I like to make things hard on myself. Until this trip I’d never had any electronic navigation gear on the boat aside from a couple 2000-era handheld GPS units. All of our plotting was done by hand on paper charts, some of them a little more out of date than they should have been. This worked well enough- it got us 5,000nm from New Orleans to Maine and back, but it did make for occasionally high-stress piloting! With the advent of cheap and functional tablet computers and navigation software to match I felt it was time for a small safety investment and before this trip I began digging into the (largely online) trove of information on tablet navigation. From what I could find it seemed possible to buy an Android tablet with built-in GPS and enough computing power to (slowly) run navigational software for under $200. At that price it was becoming increasingly hard to justify my somewhat risky reliance on outdated chartbooks!
As luck would have it while I was in the middle of this research I got a call from a sailing friend who was also interested in tablet navigation and wanted my advice. He made me a great offer- do the research, make the orders, put everything together and install some good charting and general boat applications, and he would buy not one but two tablets- one for him and one for me.

My tablet also doubles as the word processor I’m writing this on

A month later I’m leeching wifi from a closed coffeeshop in Fort Meyers and using a bluetooth keyboard to type this up on a Samsung Galaxy Tab S which has become my new navigation instrument and onboard computer. At $500 it was over twice the price of the units I was initially looking at but it also has well over twice the computing power. This means that charts load faster and there is less chance of the program lagging at a crucial moment. I also get the relative assurance of a much higher quality product- of course I’ve still got my handheld GPS units and paper charts but I’m much less likely to need to pull them out than I would be with a sub-$200 no-name tablet. There’s another crucial benefit to the $500 version; for another $26 I was able to buy a quite decent drop and water resistant case. I was very surprised how difficult it is to find a good case for Android tablets. This one (a Griffin Survivor) is still not as nice as the ostensibly submersible versions that Lifeproof makes for iPad tablets but it’s the best that I could find for any 10” Android tablet and the availability of a decent case was the crucial factor in my choice. For the friend who funded this purchase I got an iPad and a higher-quality case which is only available for iPad tablets but for various reasons I was willing to to settle for a slightly less rugged machine in order to get an Android operating system.
The main reason I wanted an Android machine was to try out the tablet version of OpenCPN. This fully open-source (and completely free!) navigational software has been available on PC computers for years but only recently has it been possible to reliably install it on Android operating systems and I wanted to try it out. Overall I’ve been very impressed. The biggest appeal is the price- the program is free and unlike every other piece of computer or tablet navigation software which make you pay for each chart area OpenCPN runs directly off the ENC or raster charts which can be downloaded from NOAA at no cost ( (the program with ENC charts for the entire US takes up about 2.5 gigabytes). OpenCPN supports a few chart formats and charts for other areas of the world can be had by hook or crook at varying cost- I haven’t explored this yet. The other thing I particularly like about OpenCPN is the mindset behind it- the program is crafted from and run on open-source software that has been developed by thousands of volunteers and although it can be buggy it is also constantly evolving.

Despite a somewhat clunky interface compared to higher-dollar navigation apps (the very slick interface on tablet versions of Navionics comes to mind) at a basic level OpenCPN is surprisingly simple and intuitive. I was expecting the touchscreen interface to be quite limiting but for the basic routeplanning and navigation I’ve been doing it is totally adequate. Basic functions like measuring distances, setting waypoints, and activating routes are done by tapping a finger or tapping and holding to select an option. Within the various option and settings windows things get a bit more complicated. One of the advantages to open-source software is that the zeitgeist behind it tends towards offering the user as many options as possible and this is true of OpenCPN. Although functionality is still limited compared to the PC version in the various settings menus you can change a great many things including exactly what information is and isn’t displayed on the chart at any given resolution and the size and font of almost every type of data on an ENC chart. Tinkerers will love this. The flip side is that coders working for free tend to be more interested in expanding functionality than making things easy for the less computer literate. Labyrinthine settings menus and opaque labeling like ‘Console Value’ or ‘ObjectQuery’ can make settings changes a real slog; it took me a full half-hour to figure out how to enlarge the tiny numbers used to display depth to a size where I could read them at night.

Deep in the settings menu

The other major disadvantage as compared to a paid program is that the Android version of OpenCPN is still quite buggy. There are regular crashes and certain fields (the all-important speed and course over ground display in particular) often disappears and force me to restart the program. This is where I’m particularly glad to have the more expensive, faster tablet; while needing to frequently close and reopen the program sounds bad on paper in practise these restarts take less than ten seconds and I’ve never lost any important information when doing this.

Our route when dodging a lightning storm south of Apilachicola. Note the occasional breaks- I haven’t figured out if this is due to a glitch in the program or temporary loss of GPS signal

OpenCPN also supports route tracking and many more high-tech features, most of which I haven’t explored. It can talk to NMEA equiptment and other gear as well as having support for Bluetooth and onboard networked devices. I do have a Bluetooth GPS unit which I bought a couple years back for a less-successful attempt at chartplotting with a netbook computer and it works flawlessly with the program. Initially I used it in order to get a faster, higher quality GPS signal to augment the built-in GPS on the tablet but after coming in from one three day offshore passage with seamless GPS coverage and realizing I had accidentally left it turned off I have been using it less and less.

Alhough they are constantly improving I’ve never used an electronic navigation device that doesn’t make occasional GPS errors. Here we are hard aground in the middle of Sanibel Island; I’ve just booted up the tablet and it has not yet gotten a reliable GPS fix. Typically it takes less than thirty seconds to get a good initial fix, even when using only the built-in GPS

There’s no question in my mind that some of the paid navigation apps available on iPad and Android systems are functionally superior to OpenCPN and when compared to the cost of chart chips on a traditional chartplotter they are still great value for the money. But they’re not cheap either; it’s easy to spend over $150 on one of the better apps with a couple chart areas and some of that is a subscription fee which requires yearly renewal. For a completely free program OpenCPN is a very impressive and highly functional alternative. I may be blogging about it but I’m still a relative luddite when it comes to this stuff and I wouldn’t actually use most of the features that come with the paid programs. OpenCPN does everything I need and more. I was wary at first about relying on it but after about 600nm I now use it for all of our navigation. I still have the paper charts and I keep a running log in case we were struck by lightning or some other catastrophe and had to resort to dead reckoning but in practise my dog-eared old charts stay stowed and I get much more sleep than I used to on night passages and sweat much less during night entrances! Folks who expect to use their electronic chartplotter like the GPS in a car may not be as impressed but for routeplanning and general plotting and piloting I think that a tablet running OpenCPN is an excellent and affordable choice for a primary navigation device. There are a host of other benefits to having a tablet onboard including apps for weather routing, GRIB forecasts and ActiveCaptain (a sort of constantly updated crowd sourced cruising guide/information database) among many others.

We’ve taken to calling 3M Dual Lock the ‘magic velcro’

Last but not least, with a $2 investment in 3M Dual Lock velcro I can have my chartplotter mounted either inside at eye level or in the cockpit. With the case I feel comfortable using it in my open cockpit in all but the worst weather. Used carefully (ie. screen not always on) I can get twelve hours out of a single charge and the tablet charges fully in a couple hours from a USB port. I use a permanently mounted charging port from BlueSea which cost around $20 and has two USB ports that run directly off my 12V house battery. In terms of consumption the tablet pulls less than one and a half amps at 12V. Granted, the screen is not nearly as visible in bright light as traditional chartplotters but good luck finding a dedicated chartplotter that can run on 15 watts!

This article was syndicated from Safe At Harbour But Meant For The Sea: DIY Sailing with Paul Calder


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