Seaplanes were the best solution in the times when long airfields didn't exist. I still believe in the future of seaplanes as a commercial transport. Existing airfields get a lot of complains about being noisy. Airfields near large cities are hard to get to. There are many traffic jams near those airfields.
But seaplanes have one big disadvantage. They need more power than a landplane to get off the water surface. Riding a wave to get airborne takes a lot of power. Parasites can change this.
What could help a seaplane getting out of the water? I guess two things can. Extra wing or extra power. Both put a weight penalty on the plane so it will not perform at cruise speed. So I thought about making the plane out of two parts. The "Slipwing" of Noël Pemberton Billing was my inspiration. The design mentioned in the "Weird aviation designs"-section of this site is not a seaplane. But Billing designed a huge slipwing commercial seaplane. Pity he stopped the design with the design of the plane and its slipwing. This sort of design also needs a new type of airport. So here I go with my thoughts.
I see a sea-airport on a shore. It has a small landing strip on the land and it has a harbor for the seaplanes. The seaplanes are locked into the harbor into some rig. An airplane (for there on I call it the slipwing) with excellent low speed performance and low noise is put on top of the seaplane. Connected, both leave the harbor. The slipwing helps to push the seaplane over the water. Ones the seaplane is airborne the drag of the water doesn't exist on more on the seaplane. The seaplane which has the wing area and power plants of a "normal" (1) landplane can now climb steadily towards its operational height on its own. The slipwing disconnects. It flies to the small landing strip on the land. Once landed it can taxi towards the rigs in the harbor and be put on top of a next seaplane. I think there could be a design made where it rolls on its own power over the seaplane and guides itself into the connection points.
I think that the slipwing should be a landplane with a large wing area and a strong power plant, which produces less noise. I was thinking about ducted fans. It has the advantage that there are no rotating parts on the outside. So there should not be a problem during disconnection. Ducted fans have the advantage that the prop can be smaller than on open propellers. This can lead to compact slipwings on the back on a seaplane. Ducted fans have the disadvantage that they should be operated in a small speed range. This is not a disadvantage in this concept. The slipwing takes off with the seaplane, disconnects and lands as soon as possible. It has not the chance to gain higher speed. [Editor (Koen)]: As you can see in the pictures, I changed me mind a bit about this. I made the slipwing into a gyrocopter. Why? Just adding power for take-off from the water, not adding wingarea. I guess it will be a bit too much drag if I would do that.
Who can make benefit from this sort of air traffic? I think that both people transport and cargo transport can gain a lot with this concept. It could be used in small size on ferry-routes (The Channel?) and it could be used in larger sizes on trans-continental routes.
A disadvantage is that both airports need to have the same structure. It has to be a sea-airport and it should have the same rigs and maybe even the same slipwings (or another design which uses the same connection points). Storms over the water with high waves that block transport on sea are of course also a disadvantage.
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(1) I place normal between "“, because I think that airplanes today have too much power. They have need for this to climb faster. The sea-airports make this not necessary. Above sea you can climb less hard because no one who can complain about the noise is living under the airway.