To try to resolve the H-4's hydrodynamic issues, in 1915 Porte carried out a series of experiments on four H-4s fitted with a variety of modified hulls, using the results of these tests to design a new 36 feet hull which was fitted to the wings and tail of an H-4, serial number 3580, with a pair of 150 hp (112 kW) Hispano-Suiza 8 engines as the Felixstowe F.1.