I've you've got useable connectivity, you can make phone calls with VoIP. People do that all the time with Skype and Whatsapp and plenty of other apps. You can have a softphone on your computer or cellphone which would allow you to make or take phone calls like a regular land line. Bria Mobile from Counterpath is a good example of a softphone you could run over broadband on either a laptop or a smartphone.You are sitting on a boat in the middle of the ocean without phone but with full broadband. How do u use the broadband to save your life?
Maybe call your local home port or nationwide 911 service and let them coordinate a rescue?
BTW, 911 emergency service does work in some countries besides the US or Canada -- we use it in Costa Rica similar to how one might in the US, to quickly reach the police or ambulance service.