Oh finally I get it. I read this a couple of years ago and it was supposed to be all about God. But no, it's not a religious allegory at all. It's about the collapse of communism. As the ocean liner of communism sinks under the weight of its own massive incompetence (a good idea, but the captain was drunk and the crew were sticky-fingered rascals), you leap overboard, clamber on to the only available boat (capitalism) only to find that there's a giant tiger on board which will eat you unless you can keep feeding it your hapless fellow-creatures. 
 When I thought this novel was about God I gave it 2 stars. It didn't make sense. But now I realise - it's a perfect metaphor - three stars.