When Captain Will Whatley guides a ship through Arctic waters, he is starkly aware of what can go wrong.Double the manpower is needed to navigate. Lookout shifts are kept to just one hour, so sailors don't lose concentration and miss a mass of floating ice. Big icebergs show up on radar, but smaller, truck-sized "bergy bits"—even more dangerous—can be missed, the captain says.The cold can freeze equipment and the earth's magnetic field disrupts compasses. If anything goes wrong…