Sounds like a rather silly requirement. If you ask me, chartplotters give folks a false sense of security. Also, a handheld GPS is a much more robust device; it's electrically isolated from the rest of the boat, it's light and physically isolated (a.k.a., it can move rather than have to resist the full impact of something hitting it), and it forces one to look at the actual paper charts (true even with plotter-type handheld, since the screens are so small).
Sorry to go OT... in the US paper charts are overrated and I consider THEM backup to my chartplotter and PC these days. My PC has the absolute, latest greatest NOAA charts on it using Rosepoint Coastal Navigator. I guess I could spend a lot of money each year to buy updated paper charts, but they may become outdated within a few months of buying them. I can update the chip on my chartplotter yearly for the same price as the paper chartbooks. Don't get me wrong - I carry paper charts for all of the areas we are in, and at night we plot our position on them every 20-30 minutes, but why would you pick paper charts, or a portable GPS with a 3" screen, as a primary navigation device when you can use a full featured chartplotter to show you your position and course, all nav marks around you or ahead of you (without flipping pages), overhead photos of marinas/anchorages/landmarks, integrated radar overlayed on the charts so you can confirm your position relative to nav aids or channels, etc.
I carry a chartplotter, two rail mounted GPS antennas, a radar, a handheld GPS (Garmin Oregon) and my laptop. AND if all that fails I have my paper charts to fall back on - but I would not use them as primary these days (maybe 7-8 years ago I would have used them as primary). I would be comfortable carrying just my chartplotter/radar and paper charts too.
As I said above, though - this is relevant to the US only. In the Bahamas, for example, I primaried off of my paper Explorer charts and used my chartplotter and handheld for lat/long. This is because my Raymarine chartplotter uses Navionics which has horrible Bahamas charts. If it was a Garmin or c-map based plotter I would have primaried off of it.
Anyway... back to regularly scheduled programming...