Why the "Step"?

I decided that in the interest of me posting more, that I'd change my writing strategy. Instead of doing infrequent long posts, I'm going to try to do daily short posts. Perhaps every once and a while I will do a novel, but for now, I will change to something akin to the "Fact-a-Day" method.

For my first act, I'm going to answer the seldom asked question, "why do flying boat hulls have the step on the bottom?" The step is the abrupt decrease in the hull chord usually about midway down the bottom of the aircraft, as can be seen on the Bombardier 415 in the picture above. First it is important to understand the difference between a flying boat and a float or seaplane. Put quite simply, a flying boat is a plane that lands directly on its hull into the water, just like a boat (who would have guessed?). A flying boat is (I am pretty sure) always primarily designed to be mainly operated on water, although most also have retractable landing gear for landing on tera firma. A float plane or sea plane usually lands on floats that are positioned similarly to traditional landing gear, and can be originally designed for use on land and then retrofitted with floats. Here is an example:

So now that we have that clear, the step on a flying boat or actually on all floats, its designed to aid the plane in breaking away from water during takeoff. When the plane is attempting to takeoff, two forces try their best to keep the hull or float firmly attached to the water's surface: adhesion and vacuum pressure. Adhesion is of course the molecular attraction between water molecules and other compounds. The vacuum pressure is caused when the aircraft pulls up on the water's surface without allowing air into a pocket under the hull, creating a low pressure (which causes the water to "pull down" on the aircraft). In calm seas, vacuum pressure is a particularly annoying problem since when the water is choppy, there won't usually be an airtight seal between the water and the hull. By adding a step, the hull is no longer a long, continuous surface. Thus when the aircraft is at speed, the water flow is broken up underneath the hull, lessening the strength of adhesion and vacuum pressure.

In addition to the step, most flying boats in particular have "breather tubes" which are located just aft of the step. These tubes run from the bottom of the hull to another location on the aircraft that is always exposed to open air. In turn, the spot most prone to vacuum pressure (the area just behind the step) can never form a low pressure as air will be immediately drawn into the pocket through the breather tubes. The tubes can be seem in the picture at this link if you zoom in and look closely behind the step on the hull: http://cdn-www.airliners.net/aviation-photos/photos/1/7/6/0770671.jpg