I am building a twin engine airboat using 2 .40ci engines, swinging 11x7" props. Normally my design called for the engine drivshafts to be spaced 12" apart to allow 1" clearance between props, as you can see this makes for a possibility to have a very nstable boat with that much weight spread out about 6 inches above the hull. What i am wondering is if i can recess on engine in it's nacelle enough to allow me to space the enignes closer to actually allow the prosp to over lap by about 2.5" to bring them closer together. I am wondering if the thrust developed in that overlap area will create an imbalance in that same area for the second prop due to the air allready being accelerated by the first. ie will this cause mass vibration??