The Bobbsey Twins on a Houseboat was published in 1915 and represents one of the more genuinely fun premises in the series. Mr. Bobbsey rents a houseboat for the summer holidays, and the entire family, plus Dinah and Sam, travel down a river and across a connected lake system, living on board for weeks at a time. The houseboat itself, called The Bluebird, becomes effectively the setting for the whole novel.
The book is structured as a series of small adventures at the various stops along the route. A near-collision with a tugboat. A storm that almost beaches them on an unmarked sandbar. A wild man on the riverbank turns out to be a perfectly polite hermit. Flossie and Freddie wander away in nearly every chapter and are recovered in slightly different circumstances each time. There is a low-key mystery involving an item missing from the houseboat after a visitor’s stay. Standard middle-period Bobbsey writing in a slightly above-average setting.