Yacht Zen Again: SaiLog YDVR NMEA-2000 Data Plotting

Friday, 27 March 2020

SaiLog YDVR NMEA-2000 Data Plotting

Hi everyone,
We've been keeping ourselves busy in isolation aboard Zen Again here in Gosport Premier Marina. The topic of this post is how we plot the data we record on our NMEA-2000 network. Yes, back to technical posts!

Zen Again's New Home

Voyage Recorder

Last year we added a Yacht Devices Voyage Recorder (YDVR) to our network. The device is small with a microSD card plugged in the the end of the unit. An LED shows whether data is being written. The unit can also record audio, with a jack at the end of the unit.

YDVR - NMEA-2000 connector indicates its size

The YDVR records all NMEA-2000 data on the network. On Zen Again this includes the following devices and data:

Vesper XB8000 AIS

Garmin GPSmap451 Chart Plotter

Garmin VHF300iAIS VHF Transceiver

Airmar DST800 Speed/Depth Transducer

Depth
Speed
Log

Airmar 220WX Weather Station

GPS
3D Attitude
3D Attitude Rate
Air Temperature
Air Pressure

As the above list shows, there's a lot of data. We have three sources of GPS information - currently at 1Hz from the GPSmap, 2Hz from the Vesper and 4Hz from the 220WX. AIS is another source of substantial data. We are using a 32GB microSD card.

The YVDR is configurable to...

enable/disable NMEA-2000 recording (ie for audio only)
DAT/CAN file format
AIS on/off (AIS generates a lot of data)
ignore nominated NMEA-2000 PGNs (to ignore particular data types)
ignore address (to ignore particular devices)
enable/disable audio
adjust audio settings
& more

The YDVR comes with Windows and Mac OS X apps called YVDRconv. The app translates the microSD data files into a variety of formats. We convert to CanBoat/SignalK log file format which looks like this...

YVDRconv Output Format snippet

Zen Again's log files consume about 20MB/hour. For our recent passage from London to Gosport the log file is about 800MB. Given we were in a busy area much of this data may be AIS.

Having recorded the data the question was what can we do with the data? Our goal was to produce plots showing boat performance and the environment in which we were sailing. Searching the internet didn't produce anything which looked ideal, although there must be SignalK apps for this somewhere.

SaiLog Plot

We developed a Python script to add to our SaiLog python suite. Example plots below show our passage from London to Gosport (click on each for full detail)...

London to Gosport Passage - Environment Plot

The environment plot's wind sub-plots clearly show the nice SW wind we enjoyed on day 1, the light winds overnight and the slowly building NE wind on day 2 which was very gusty. The water and air temperatures show it was indeed chilly!

London to Gosport Passage - Performance Plot

The performance plot's speed sub-plot clearly shows the effect of currents during the passage. The heel angle sub-plot shows when seas were present.

SaiLog Plot currently plots selected data from our DST800 and 220WX devices. All NMEA-2000 data is marked with its source address, which allows us to select the data.

Using YVDRconv

Using YVDRconv is quite simple. On opening the app there's a welcome page for the conversion wizard...

YVDRconv page 1

The trickiest step is selecting the files to import on the next page. The YVDR splits files into a time series of folders. We had to select files from several folders, using the dates of each file to ensure we had all data from our passage time window...

YVDRconv page 2

On page 3 the output format is selected. We use SignalK log format since we hope to be using SignalK soon, and the format is readily parsed in Python scripts.