You can also disable "Find my iPhone" if you log into your iCloud account on your computer.
iCloud: Remove your device from Find My iPhone
Since you are on a vessel, this is one reason why you don't see a map on your phone. The phone needs to get an exact location to show you a map.
The built in GPS can only do that if there is a cellular data network connection or a Wi-Fi network that can provide the information for the location.
The phone can't detect the GPS signal provided by the GPS satellites, like for example the navigation system on your ship.
As soon as you will get a connection to a cellular network again, maps and "Find my iPhone " will be able to show the actual position on a map.
iPhone GPS Support
The iPhone 3G and all subsequently released iPhone models use A-GPS -- or "Assisted GPS" -- which in basic terms accesses an intermediary server when it is not possible to connect directly via satellite -- indoors, for example -- and this server provides the nearest satellite with additional information to make it possible to more accurately determine a users position.
Apple explains that the iPhone 3G and all later models also use "wi-fi hotspots and cellular towers to get the most accurate location fast" when GPS is not the most convenient method of location detection. The iPhone 3GS and later iPhone models additionally have an integrated digital compass to also provide the direction one is facing, which is quite useful when combined with mapping software.
copied from What is GPS? How does the iPhone GPS system work?