There's an existing HF service called SailMail.[1] This is email for sailboats over HF. There are about 20 fixed stations around the world maintained by the organization. Cost is $275 per vessel per year. You can use 90 minutes of connect time per week. All it does is email over the HF links. There are now some satellite options which interoperate with it, but it predates those. There's very little infrastructure; the boat-side equipment is an SSB transceiver, and the shore stations are quite modest.

It was set up by Stan Honey, who invented car navigation systems (Etak) and the thing that puts the yellow line on TV views of football fields (Sportsvision). He's into long-distance sailing, and wanted some basic comms that would work on most of the world's oceans.

It's not that advanced technically. It just works.

[1] https://sailmail.com/