If you don’t want to rely on Cellular but still want internet, I think your only other option is WiFi as WAN, using something like Ubiquiti directional antenna’s on both boat and shore if needed.
I’m not sure if there is a satellite internet that doesn’t require a phone uplink, so I don’t think satellite would work?
Edit: maybe HughsNet?
Or skip the internet altogether and just use Out of the Box SmartThings devices and Apps that can run local.