Hello,
Is my understanding correct that you want to connect your RUT955 to the marina Wi-Fi and use it as your primary internet source? In other words, the RUT955 should use the marina Wi-Fi as the main internet source and switch to the cellular mobile connection only when the marina Wi-Fi is unavailable.
If that is the case, you can configure the RUT955 as a Wireless Client (STA mode) and connect it to the marina Wi-Fi. This setup will allow devices connected to the RUT955 LAN network (for example, Wi-Fi) to access the internet, as the RUT955 will be using the marina Wi-Fi as its WAN.
Then you can configure failover where wireless WAN will be your main WAN, and mobile (mob1s1a1) will be your secondary failover interface.
I suggest watching our YouTube video here. The video explains the configuration process in detail.
Kind Regards,
Andzej