Fliegen Works, and its predecessor company Volant Technica, has performed structural analysis and testing for twin seaplane float installations. We recently completed an STC for Joel Wattum to install TSOed Aerocet 2200 floats on the Cessna 170A & 170B. A slick set of modern twin seaplane floats for a good aircraft.
Things we consider when installing straight floats include TSO limitations, water loads, strut strength, attachment fitting strength, flying wires, and the fuselage attachment strength. Aircraft that have not previously been on floats also need to have structural upgrades, especially the engine mount area and rear float attachment area. The water loads include 4 loading conditions and the bow landing condition usually increases the loads on the engine mount. Also considered are the water rudder rigging and retraction systems. There are other aspects of float installations including an Aircraft Flight Manual Supplement (AFMS), Instructions for Continued Airworthiness (ICA – maintenance manual), flight testing, and do not forget an anchor light!
Amphibious floats also require review of the landing loads, hydraulic systems, retraction systems, and gear advisory systems. The flight test requirements are higher since the landing distances often need to be determined.
Twin seaplane floats are certified to TSO C27 by the float manufacturer. If you are designing a new set of floats, Fliegen Works can help develop the loads, drawings, and test plans.