Connell uses figurative language in the very beginning to create the mood of suspicion. He does this most effectively with the repetition of the idea that it is extremely dark, a place wherein we are all afraid.
He uses simile:
It's like moist black velvet.
To display personification, Rainsford found himself:
trying to peer through the dank tropical night that was palpable as it pressed its thick warm blackness in upon the yacht.
Darkness can't press itself on anything.
Further on, Rainsford finds himself alone on deck in his own confidence and narration reports of him:
There was no sound in the night as Rainsford sat there but the muffled throb of the engine that drove the yacht swiftly through the darkness, and the swish and ripple of the wash of the propeller.
You can almost feel that kind of dark, that which you can't see. I think this repetition demonstrates another aspect of figurative language: the symbol. Darkness is often a symbol for evil, and although Whitney said it, Rainsford hasn't experienced it... yet. This brings plot into play. We are being set up to agree with Rainsford because we like heroes. This is what makes the story rich: both sides are presented, the evil he is about to encounter and his ability to overcome evil. The author most effectively presents this possibility through figurative language.