I am thinking Ipad or Galaxy Tab in particular. I was thinking of say a Ram Mount - eg http://www.ram-mount.com/NewProducts...5/Default.aspx and then a waterproof case that would still allow touch screen use, but would (without damage to it) fit into the mount...given the insanely cheap mapping from Navionics, the screen size and speed and the true GPS this would be a great way to Navigate. I would definitely want it waterproofed though...
Cheers