Why does insurance for seaplanes and helicopters cost more than for fixed wing landplanes?
Seaplanes and helicopters make up a very small part of the light aircraft population, so underwriters have a smaller number of units over which to spread the cost of the inevitable losses. Seaplanes and helicopters also tend to operate down low where they are likely to collide with things like birds, wires, towers and submerged objects. Helicopter claims tend to be expensive because so much of the helicopter is moving. Seaplanes and amphibian claims often involve total immersion of the airframe in water, requiring time consuming repairs to radios, electrical systems, and anti corrosion measures.
