I've been playing around with using PC software for navigation and thought to share what I have found.
So far my preferred software is Open CPN (free) at
www.opencpn.org a really useful program that can pretty well do anything I want it to, will accept (obviously) GPS for position and tracking etc, AIS, Radar, grib files, weather fax, all sorts of fun things via plugins - full details on their web site.
It is necessary to add your own charts and it will accept a whole variety of different types. I’ve found these on the internet (free again) - full world highly detailed charts. Is in six parts, simply open them up and down load all 6 (as the page opens, ignore all the bumph and just click the ‘go to file’ box).
(NB. Just found that the link will try and open an advertising page (blank), just close it and the proper screen is under it. Just then click on the CM93 multi part .rar file to download it).
http://www.firedrive.com/file/38AF4AF46C53B9C8http://www.firedrive.com/file/626993A82D094F15http://www.firedrive.com/file/EE258CA9D6D0F4C3http://www.firedrive.com/file/7C86A23998727563http://www.firedrive.com/file/1CC22D10FBC2816Fhttp://www.firedrive.com/file/A1E4C9CCBA977FCCAlthough together they are over 1 gig they will still need to be decompressed.
In Open Cpn its very easy to add the charts - make sure you get all the decompressed files in one folder
In the charts options menu open up the vector charts menu - I selected ‘show all’ but you can select any level of detail you want. Also make sure you click on the ENC text box in the main menu bar to show all the text detail on the chart, also make sure you have graphic acceleration (opengl) ticked in the display menu.
I also use BSB charts for UK that I got off Visit My Harbour for about £40 on an annually updatable memory stick that works fantastically with Open CPN with my Garmin 76cx plugged in.
Another brilliant program I have found is GE2kap
http://www.gdayii.ca/Downloads.phpThis will allow you to create your own charts off Google Earth, the chap who wrote it asks for a very well deserved USD20 donation, which I am sending. But I am sure he won’t mind if you try it out. With this program it is also possible to overlay a marine chart - such as CM93 or BSB onto a google earth image, all referenced and extremely accurate - very handy if your charts are a little suspect or out of date. (You guys who sail down in the Med may find that useful, especially around the greek islands?).
I have the instructions to do this, if any one is interested in doing it then give me a shout.

I'm trying to attach a chart I created as an experiment of Rutland Water when sailing last weekend with Peter C, obviously there are no charts of the area, so I just made one! - we did 16 miles, at an average speed of 4 knots, peaking to 6.5 knots if you're interested!
You will need a program called ooRexx-4.1.1-windows.x86_32 to run GE2KAP.
http://sourceforge.net/projects/oorexx/files/oorexx/4.1.1/Goodness knows what it is or why you need it, but you do!
I’m far from being a computer whiz or geek type, but I found it all very easy to do and quite interesting - in a sad way, and apart from the charts I bought myself, all free!
Hope this is of some use to anyone, as I say I am not in any way a competent person around this software and I’ve not added any ‘how to’s’ in this post, as is mostly self explanatory, but if you do get stuck give me a shout and I may be able to help, but there is a very sophisticated Open CPN forum on Cruiser Forum.. Just google it.
By the way, I understand these charts are 2009. Apparently there are 2012 charts out there somewhere if any one knows where?.. Usual cautions in using electronic charts for navigation. I actually use a Yeoman chart plotter (paper based) for real time navigation working alongside all this stuff.
Andy
Added another shot of a GE2KAP 'chart' of my own creek area overlaid onto CM93 - now I know how to do it! - just need to sort out the transparency...
You can see at the bottom left of the shot how accurately the two join up..the sea defence bank is clearly defined in both images and line up accurately.. the top left of the google shot is a bit more hazy.. but that area is in fact beach/dune/marsh area that regularly changes around..
From my little screen shots of the CM93 charts (all taken off my little 10 ins screen netbook) you can see the level of detail on them.. and that is the same for the whole world!