Problems with opencpn-watchdog under linux

[kinefou]

Hello,
I use opencpn on raspberry pi. I installed a receiver based on rtl-sdr key that works perfectly. For my solitary sailing, I would have liked to be able to couple an alarm thanks to the couple 'draw-watchdog' that would allow me to trigger an action if a cargo ship came across my road while I would take a few minutes of rest!
So I installed all this and despite desperate attempts, nothing happens when a cargo ship enters my guard zone!
I'm afraid of cargo ships !!!
Of spite, I redid the same installation on opencpn 5 windows, and there, everything works to the wishes, the alarms are triggered as soon as an intruder enters my zone !!
Fervent defender of Linux, I do not want to admit any supremacy to Windows !!!
I redo the same installation on linux Mint 19 and there, as on the raspberry, nothing happens and the cargo ship comes with impunity cut in half without even warning me !!
Is there a bug in the plugin or in Opencpn linux ??
Thank you kindly reassure me and allow me to sleep a little during my cruises!!
cordially