Now add a cellular broadband capability. There are a few approaches depending on the degree of integration and off-boat portability you want.

A router that supports a USB broadband card can be fully integrated in the boat network, whereas a WiFi hotspot such as the Verizon JetPack will be completely portable (and has its own battery) so you can use it anywhere (airport/café/hotel) to support concurrent connections to multiple PCs and tablets.