We got our first trawler at the end of last season, 2004 Mainship 400. I have a Raymarine C80 chart plotter at the upper helm. Last couple of times out it started acting up. Powers up fine but sometimes will not start updating or showing navigation for 30-45 minutes. Sometime it will start off navigating at start up then stop navigating after an hour or so and just show last screen. Might start navigating again after a while or just stay on last location screen (my cruise during this time have been only around 2 hours or so). Could this be as simple as the GPS puck or does it sound more serious? Any advice from the experienced folks here is appreciated.