The evidence from the passage that shows that being in the water gives Harborough a new perspective is:
“Behind me the Peterhof towered, like a cliff; I had never realised, before, how big a five-thousand-ton vessel looks from the water.”
This statement illustrates how Harborough’s viewpoint has changed now that he is in the water, allowing him to see the ship from a different angle and appreciate its size in a way he hadn't before.