One of the problems associated with long planing hulls is their inability to rotate into a take off attitude. Many poorly designed hulls and/or floats have this problem and the solution is that the wing must be set into the take-off position while the hull or floats are relatively level. Many models can overcome the problem with lots of power but lightly powered planes must be more scientific inthe way they are rigged. The Martin Mars, which I watch fly every summer is like this. At rest the wing is in a fairly positive angle of attack. As the plane accelerates the nose rises and the plane accelerates until the aft end of the fuselage is clear of the water and the fuselage is back to a fairly level attitude at which point it continues to accelerate until it reaches flying speed at which point it flys off with minimal rotation. The Mars has been described by others as a giant powered glider. Watching it fly it is easy to see why it is described so because it flys so slowly. It has thousands of horsepower but it also has tons of wing area which must give it a very light wing loading. When water bombing it initially takes off empty of water and then scoops up tons of water on a pick up pass. I don't know if the Mars qualifies as a long planing hull since I have never actually analyzed it's length-beam ratio but it must be close. Every sea plane enthusiast should make an effort to watch that beauty in action.
Peter