MR2100 WiFi router - how to keep WiFi on outside of celular coverage

Hi I have a MR2100 in a marine application where it is acting as the WiFi hub for the vessels nav systems using cellular connection to the internet when available and facilitating comms between the various navigation systems. The problem I am having is when the vessel moves outside of cellular range the WiFi hotspot turns off thus stopping the nav systems being able to communicate with each other and thus function correctly. Is there a way to force the WiFI to stay on permanently?

Thanks,

Graeme.