The market is small, there are existing competitors, and things change slowly. I also suspect that there isn't much value that startup could bring. I bet there are fancy products for fancy yachts.
There is a lot of open source going on. There is OpenCPN chart plotter. There is also NMEA OneNet which uses Ethernet so should support things that radars, plus make wiring easier.
Perhaps still a big enough space for a bootstrapped indie business, for lack of VC scale.
NMEA is quite interesting, though. Coupled with Czone for digital switching and power readings, I bet there is some interesting insight waiting to be discovered, one that can be monetized.
There is a lot of open source going on. There is OpenCPN chart plotter. There is also NMEA OneNet which uses Ethernet so should support things that radars, plus make wiring easier.