The Bobbsey Twins on a Houseboat, first published in 1915
When Mr. Bobbsey purchases a houseboat named the Bluebird, the entire family goes on a long trip down Lake Metoka to Lemby Creek and through that to Lake Romano. Cousins Harry and Dorothy joined the Bobbseys and helped to solve a mystery -- finding out what made the queer noises.
This is the sixth book in the famous series produced in the early 1900s by the Stratemeyer Syndicate. Laura Lee Hope is a pseudonym used by the Stratemeyer Syndicate for many books for children.
http://en.wikipedia.org/wiki/Laura_Lee_Hope This volume and the next 23 were written by Lilian Garis.
http://en.wikipedia.org/wiki/Bobbsey_Twins
Created from Project Gutenberg EText-No. 5948. I took the illustrations from the scanned page images at books.google.com and processed them with Paint Shop Pro to improve the contrast and resize.