The Furuno model is a 1722C. I can send you the operators manual that shows the format but it would probably be better to show you a trace of the data from a program that I wrote that does the upload properly and a trace from OpenCPN
tha fails. I talked to the Furuno people to get the correct format.
Here is trace from my program send a simple 3 point route
03:18:18 $PFEC,GPwpl,2113.691,N,08644.034,W, R0101,M,@:01test,A,,,,*7C
03:18:18 $PFEC,GPwpl,2113.833,N,08644.062,W, R0102,M,@:01test,A,,,,*7A
03:18:18 $PFEC,GPwpl,2113.832,N,08644.168,W, R0103,M,@:01test,A,,,,*71
03:18:18 $GPRTE,1,1,C,001, R0101, R0102, R0103*59
The attachment is a screenshot the OpenCPN NMEA
window after sending the same route, it also shows the route properties.
There are 4 things that I see are different other than the waypoint names:
1. There are two fields in the GPwpl that you don't send. The sixth field is the waypoint color which I set to a "M". The seventh field is a waypoint comment "@:01test" which I set to the route name. These fields may not be needed, we could try it without.
2. There is no checksum in your sentences, not sure if that is really needed, maybe not.
3. In the $GPRTE sentence the third field, the message mode in my trace is a "C" in yours its a "c" . Furuno said that for a 1722C it must be the capital C, for other models its the small c which you are sending.
4. I send a route comment GPrtc,001,,01test*44 this may not be required.
Of the 4 I think number three is the biggy. I remember when writing my program it had to be a capital "C".