Irony of island being boat shaped in Lord of the Flies?

There are a number of interpretations as to why Golding chose to describe the island as being boat shaped. It could symbolise that the boys on board the island are on a journey from schoolboys to proto-adults, or it might symbolise their journey from civilization to savagery. The irony is that they are actually going nowhere and are reliant on the arrival of a real boat to come and take them away, from the island and from the evil within themselves which threatens their very existennce..