A seaplane is defined as an airplane designed to take off from and land on water. Sea planes can be generally classified as either flying boats, or floatplanes. Those that can be op erated on both land and water are called amphibians. The floatplane is ordinarily understood to be a conventional landplane equipped with sep arate floats instead of wheels, as opposed to a flying boat in which the hull serves the dual purpose of providing buoyancy in the water and space for the pilot, crew, and passengers. The float type is the more common seaplane, particularly those with relatively low horsepow er. It may be equipped with either singly float or twin floats; however, most seaplanes are the twinboat variety. Though there is considerable difference between handling a floatplane and handling a flying boat, the theory on which the techniques are based is similar. There fore, with few exceptions, the explanations given here for one type may be considered to ap ply to the other. In the air the seaplane is operated and controlled in much the same manner as the land plane, since the only major difference between the floatplane and the landplane is the installa tion of floats instead of wheels. Generally, because of the float’s greater weight, replacing wheels with floats increases the airplane’s empty weight and thus decreases its useful load, and rate of climb.3.The most common seaplanes are （ ） ．