Unfortunately , PGN130578 coming from the SCX is proprietary. Here is the break down
PGN 130578 – Vessel Speed Components

Standard fast‑packet (12 bytes). SCX‑20 uses only ground‑referenced fields*.
Field Name Offset Length Type Resolution Units Description Notes
Longitudinal Speed (Water‑ref) 0 2 B Int16 0.001 m/s Fwd/Rev speed through water N/A on SCX‑20
Transverse Speed (Water‑ref) 2 2 B Int16 0.001 m/s Lateral water speed N/A on SCX‑20
Longitudinal Speed (Ground‑ref) 4 2 B Int16 0.001 m/s Forward speed over ground Primary value
Transverse Speed (Ground‑ref) 6 2 B Int16 0.001 m/s Side‑drift over ground Leeway component
Stern Speed (Water‑ref) 8 2 B Int16 0.001 m/s Astern water speed N/A
Stern Speed (Ground‑ref) 10 2 B Int16 0.001 m/s Astern speed over ground when reversing.
* You need to be able to send BSP in another Furuno proprietary PGN from a Furuno BSP source for it to be able to have any value for leeway calcs.  
 

Last edited by Astolfo (6/11/2025 4:56 pm)

Thanks! I’ll play around with it do see what makes more sense - I’m struggling to line up my currents from tack to tack, not sure how much of it is a compass problem and how much is a leeway problem … I’m sailing in an area with lots of natural (iron rich islands) and electric (cables) magnetic disturbance, so I got my self a satellite compass … only problem now is the Russians GPS jamming the Baltic … so not sure what will be better - but if it could solve both accurate heading and leeway it would be great 😊