This post is written for those who runs Signal K(SK), or applications that indirect are using SK, and want to write log files that could be read for later use.
Other applications could be Openplotter which includes SK or OpenCPN for example interfacing a NMEA 2000 network via SK.
There are sample files within the SK installation which can be used, for testing purposes, before you have created your own log files from your boat trips. Check here at "Input file/data".