In 1918, the vessel became Chicago's first diesel engine yacht when it was purchased by Commodore W.L. Baum of the Chicago Yacht Club and renamed Whitemarsh.

Colonel Robert H. Morse

Baum's much-heralded Whitemarsh subsequently became Rosinco when Colonel Robert Hosmer Morse acquired the vessel in 1925. Colonel Morse was an avid mariner. In 1922 he joined the Chicago Yacht Club, and three years later spent $30,000 refitting his new aquisition, already a luxurious and powerful pleasure boat.  Several years later, Morse became the club's fleet commander.

A Fairbanks-Morse Model 35 electro-diesel engine

Morse's improvements reflected his financial position and the pride he had in his company's marine engines. In 1927 the yacht received a new Fairbanks-Morse Model 35 electro-diesel engine with six 10-inch diameter cylinders, each having a 12.5-inch stroke. Introduced that year, the Model 35 engine remained in production until 1946.  The Rosinco's various improvements raised her value to about $150,000, making her a symbol of American prosperity during the Roaring Twenties.