Why did Jerome and his friends decided on a boating holiday to river Thames?

The friends decide that taking a vacation together would restore their health, and debate locations for a week-long excursion. J. suggests a rural, old-world spot, but Harris wishes to avoid remote locations and counters with the suggestion of a sea cruise. J. vetoes that idea because one week is not enough time to overcome seasickness and actually enjoy the trip. He notes to the reader that no one admits to being seasick on land, but that many people have trouble with it when actually on a ship. George suggests taking a boat trip down the Thames, an idea that everyone approves. Though J. worries that Montmorency will get bored in the boat, they decide to bring him along anyway.