Signal K data parsing

[Techstyle]

I am running OP2.5, have a GPS puck set up and have OpenCPN setup to send APB and RMB data back to signal K.  

I see many Signal K phrases parsed from the NMEA0183 RMB sentence (items 2, 6-12 from the list below), but I dont see one for Steer direction (item 3).  this component is also not parsed from APB.  what decides which parts of which sentences are parsed and How would I go about extracting that data?

RMB - Recommended Minimum Navigation Information[url=https://opencpn.org/wiki/dokuwiki/doku.php?id=opencpn:opencpn_user_manual:advanced_features:nmea_sentences#rmb_-_recommended_minimum_navigation_information][/url]
To be sent by a navigation receiver when a destination waypoint is active.
''
                                                           14
       1 2   3 4    5    6       7 8        9 10  11  12  13|  15
       | |   | |    |    |       | |        | |   |   |   | |   |
$--RMB,A,x.x,a,c--c,c--c,llll.ll,a,yyyyy.yy,a,x.x,x.x,x.x,A,m,*hh<CR><LF>''
Field Number:

1. Status, A= Active, V = Void
   
2. Cross Track error - nautical miles
   
3. Direction to Steer, Left or Right
   
4. TO Waypoint ID
   
5. FROM Waypoint ID
   
6. Destination Waypoint Latitude
   
7. N or S
   
8. Destination Waypoint Longitude
   
9. E or W
   
10. Range to destination in nautical miles
    
11. Bearing to destination in degrees True
    
12. Destination closing velocity in knots
    
13. Arrival Status, A = Arrival Circle Entered
    
14. Status A - Data Valid, V - Data Invalid, FAA mode indicator (NMEA 2.3 and later)
    

I would also be interested in calculating the ETA to next waypoint (/vessels/<RegExp>/navigation/courseRhumbline/activeRoute/estimatedTimeOfArrival) and the steer error (to go along with the Left or right steer direction)

ultimately, I would also like to calculate tidal drift using COG and GPS speed, vs heading and boat speed to be able to correct for the drift (corrected bearing to waypoint)

Thanks
Jason