Highlights from my Opencpn navigation and AIS backup seminars

Over the last two days, I (Don) gave a pair of seminars on opencpn at Shelter Bay Marina. The purpose was to review some of the features I had found useful in opencpn, help people upgrade to Version 5, and provide troubleshooting support. I asked folks to bring computers and then brought Version 5 plus a wide range of maps and charts on a thumb drive so folks could download during the seminars.

Satellite charts come as .kap and .mbtiles

There have been, and is now an ever growing, collection of satellite charts that are geo registered and can be displayed in opencpn. These will appear either as .kap or .mbtiles files.

  • The mbtiles format provides a collection of many files (tiles) in one file
  • The satellite images can be from: Google Earth, Bing, arcgis, and navionics. Many versions are available at different zoom levels (resolutions).

How to organize your files

While now there is a plethora of riches, you need to go through and curate the different files and file formats to determine what works best in your area, and organize them in a way that works for you

Some of the files will have better resolution in some areas and lower in others, so you may want to keep multiple files around.

  • If you are in the Central America region, the PanamaPosse has a collection of satellite files
  • For the Pacific you find many at svsoggypaws.com
  • Other sites have collections as well

You too can create satellite charts

If you are in an area where there are no good satellite charts, you can create your own. Paul Higgins (gdayii.ca), is a cruiser and developer and has created sat2chart (was ge2kap) which can create these files.

Chart groups bring order to your life

Once you have satellite charts and perhaps some other chart types (for example, NOAA charts), you will want to look at them, perhaps at the same time. In the current version 5 of opencpn, you have the option of displaying two charts side by side, (Options->Display->Canvas Layout) and choose the two screens. Note that you can adjust the ratio of screens by sliding the center line over.

The next thing is now that you have all these charts you will want to create Chart Groups. Chart groups are useful for many things, including reducing clutter on your screen and allowing you to be more selective in groupings. If you create a chart group for the raster charts in your area, and a second chart group for satellite, you can easily pick one chart group for one screen (right click->Chart groups->Chart group name) and then go to other and select another chart group. A short cut for this is to use the number keys (1,2,3…) will select the chart groups in order. You can also create a chart group of less favored files, since they may come in handy, but you don’t want them to clutter up your main view.

Where did my charts go?

One additional note – if you have satellite charts and other charts together, the satellite charts may always show first. You can “hide” them, if you are in quilting mode, by right clicking on the icon at the bottom for that chart and selecting hide. The reason for them displaying, is that opencpn will display charts in order of scale, and many of the satellite images I’ve found, are shown as 1:4000 while other charts range in scale from 1:5000 – 1:300,000. Again, a useful reason to split satellite charts into their own group.

Quilting mode facilitates hassle free crossing betweeen charts

Speaking of quilting — opencpn has two modes for displaying charts as well – This is known as quilting mode. If you have quilting mode off, it will show one chart at a time. With quilting mode on, the system will try and stitch the charts together to provide a seamless view as possible. However, in some cases the edges of the quilt may be blurry, so if you hit the “q” key, you can quickly toggle quilting mode on and off. When it’s off, you can click on the colored box at the bottom of the screen and it will display just the one chart you selecting.

Another little discovery just today — If you have a touch screen, the hover mode and right click are disabled, even if you have a keyboard and mouse. If you switch off touchscreen mode in the settings, it works as expected.

How to add GPS and AIS to your laptop

There are several options to add GPS and AIS running on your laptop

  1. If you have a USB plug to your NMEA network, you can plug in and receive messages
  2. Some newer plotters and AIS systems will relay messages to wifi
  3. You can get a device such as yachtd nmea 2000 repeater – a really cool little device! Based in Russia, the company has great customer service and offers a range of other cool devices. This will broadcast onto your wifi network and give you all the NMEA traffic on your handheld devices as well.

Always have a back-up

You should have a standalone system as well for a full backup.

  • Get a GPS Puck – they cost around $40, plug into USB and give you a GPS.
  • Lastly, if you have an android phone, you can download an app like Share GPS. This app will let you connect you phone to your laptop with Bluetooth. A quick setup, and it just works! And we’ve all got so many devices around these days that have built in GPS, might as well use them for backup

AIS allows you to see other vessels and your boat to be seen by others

Last bit of fun technology. Now that you have your charts, and your GPS, you’ll want AIS so you can monitor other boats and they can monitor you. In general, Nina and I feel safer transmitting our location via an AIS transponder. Commercial ships all carry and monitor AIS, and more and more cruisers do too and should. When we transmit our AIS signal, we know we will appear on a ships’ bridge with information about the size of our boat, the speed, our course, and the estimated time of collision versus a little radar blip. We’re big believers in AIS and feel all cruisers who can afford it, should both transmit and receive.

Skip a few beers out and get a USB AIS

AIS is expensive, but we feel well worth the value. But, like anything else on a boat, it can break. So again, what is your backup? We carry a small USB radio receiver called a DVB-T SDR. This is a software defined radio (which means that a program can control the radio). They cost somewhere between $8 and $30, and come with a small antenna. With this little USB device, and a small antenna, I was able to receive AIS signals for around a 4 mile radius.

I was not able to get the opencpn ais plugin to work, so I used a different solution. I made my computer into an AIS server and broadcast the AIS messages to all other devices so I could link opencpn, Navionics on several devices and sailgrib to my ais receiver. I won’t go through the whole set up, but if you look at Rtl-sdr.com, you’ll want to get Sdr# as well as aisdeco2. Sdr# is a full radio controller, but you just need it to find your frequency offset and gain. After that, you just use aisdeco2.

One last show and tell – Rudy on SV Tavae lent me a RaspberryPi that he has configured. It has a GPS puck attached and opencpn loaded. For $40 for the RaspberryPi and around $30 for the puck he has a lovely chart plotter. With an RTL-SDR attached, he can add in an AIS receiver.

It takes a village to stay safe

I’ve got to thank all of these amazing folks that have created and supported these tools. The sailing/cruiser and open source tech communities continue to share knowledge and products that keep us safe.

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