How does C.S. Forester use imagery in Admiral Hornblower in the West Indies?

Imagery:

Crab came round like a top, with lusty arms hauling in on the sheets. She lay far over to starboard, with the wind abeam, and Hornblower, one leg in his trousers, after a frantic hop, trying to preserve his balance, fell on his nose across his cot with his legs in the air. He struggled to his feet again; Crab still heeled over to starboard, farther and then less, as each roller of the beam sea passed under her, each roll taking Hornblower by surprise as he tried to put his other leg into is trousers, so that he sat down twice, abruptly, on his cot before he managed it.