Good day guys, I have been looking at the phone apps for extra navigation. Am I correct in that once installed on a smart phone you do not need a phone signal for them to operate? If so any recomendations . I have been looking at NAVIONICS + . Excuse my ignorance, oh and this is UK costal only. I do have a small 5" Garmin, Marine navigator ( from Visit my Harbour) and an old Furuno Radar with very basic GPS charts on it, so this would not be my only nav device.