In the U.S., this is a mushy area in the copyright law, but the short answer is that if you use common sense this kind of "space shifting" is likely to be viewed as a "fair use." I would not go out and sell your collection of paper charts after scanning them in, or post your scans on the Internet. In any event, our government works, including nautical charts, are not copyrighted at all.
In Canada, the government does claim Crown copyright on your nautical charts. I can't speak to Canadian copyright law but still think it's doubtful Her Majesty will care that you scanned in your own paper charts.
Honestly, I would be more concerned about cartographic concerns than legal ones.
Last edited by KeithW; 05-31-2011 at 06:16 AM.