we just used the ipad as a second chart plotter on our cruise to the Abaco's and Florida.

I find the Garmin chart app to be pretty good, especially with the added Active Captian.

I liked it as much as the stand alone plotter.

And the app was free and the explorer charts (as well as all the US charts was 40 bucks!

I don't know if it will replace the other plotter though.

Ipad is hard to read in direct sunlight, and not waterproof.

Rich