Explain fully why the fire has gone out and the consequences of this for the boys. Why are Ralph and Piggy angry?

Basically a ship passed by and the fire was left smouldering.

This really sets a showdown between Jack and Ralph. Ralph confronts Jack in front of the boys, "You let the bloody fire out!" There was a ship. It takes time for the boys to comprehend the full effect of this. The littluns begin to cry and this filters to the others. Unfortunately Jack is able to deflect the negativity by humiliating Piggy.