Survivor case. Both because it is reasonable priced and it fits the iPad 3 (even if not stated explicitly on the package). An alternative - the Lifeproof case, not available for iPad 3 yet , looks pretty good, but is slightly more expensive.
After testing it outdoors, I already suspect one problem - sun reflections. With direct sunlight and a small angle, the plastic screen cover very quickly turns into a mirror.
The apps ? Navionics Marine HD of course. Its is a must and have integrated weather forecast which is a huge advantage. In addition Havneguiden (Harbour Guide) which is an excellent guide to all harbors in Scandinavia. Finally, I can recommend the Windfinder app on iPhone - it provides real time weather data from several weather stations along the coast.