I have emailed Navionics begging them to release their app for Xoom.
Last weekend I extracted the .apk from my rooted Desire Z and installed in on my Xoom without any problems at all. I then used the Xoom to plot a route, and then jumped into my boat and used the Xoom to navigate for 3,5 hours. No problems at all, despite Navionics saying the app at the moment is not compatible with the Xoom.
If I understood them correctly they are working on a tablet version due to be released later, but in the mean time I don't see why they can't just change the app data on Market to allow it to be downloaded and installed on all handsets and tablets - they might just write a short disclaimer about it haven't been tested on tablets.