Ephraim had thought about it—about what could happen to them if he screws up one more time. If he would finally burn the whole ship and leave them all charred. He had thought about it so much that he was unable to focus. To concentrate. To call upon Nar. Nothing was happening—no embers, no voice of the dragon, just the chaos on his mind.
What if he fails?
What if he burns the ship again?
There's no guarantee whether he would be able to do it correctly since he screwed up the first time. Casting a barrier to envelop the whole ship to be able to have it float back above the waters was a task Ephraim was unsure to do. Even if he would be successful enough to let it float above the water, there is still the fact that they would just be stranded to the freezing ocean if there are no ship in sight.
