At the end of the journey
(Book)

"Set in the Black tide rising world created by John Ringo."

"It was supposed to be fun. Six teenagers and their British captain aboard the ketch Crosscurrent Voyager, headed on a senior year summer cruise to excitement and adventure. Then the world as they knew it ended. A plague spread throughout the globe, killing millions and turning the survivors into cannibalistic rage monsters-zombies, in so many words. Only by putting aside their differences were the young crew able to survive. Now, they seek others like them, those fortunate souls who have made it through the zombie apocalypse. After all, maybe it's not the end of the world so long as GPS can help survivors navigate deadly terrain, to link up, and maybe-just maybe-ensure the continuation of the human race. But the Earth's GPS systems are failing. It falls to those aboard the Crosscurrent Voyager to keep the unthinkable from happening. In order to do so, they must traverse dangerous seas to a European Space Agency complex in French Guiana. And thousands of infected stand in the way. If they succeed, humankind has a chance of rebuiling. If they fail, humanity may well be at the end of its journey." --publisher's website