If you want to try something for free...SEA CLEAR is available for free download and uses all the free US charts so you can do what you want to absolutely free for the charts and the software.
Here's thelink you need for the download and more info.
http://www.sping.com/seaclear/
PS...I KNOW THIS IS A DEAD AND RESURRECTED THREAD BUT THE LINK IS GOOD FOR NEW FOLKS TOO!