If you need a plotter but do not have one .
a laptop that you can use in a cabin not waterproof
or a Panasonic water proof laptop .
then here is a link to a free setup.
it may take a while to get set up but with a GPS receiver it works very very well.
this uses all the favorite charts ...
when this is installed you can pick any number of online maps to use including the Navionics charts and Sonar-map online maps and you can even do land overlays of satellite imagery from Bing or Google.and many others satellite images
FOR FREE give it a go even as a backup system...