RE: Thrust angle for sea plane??
All the flying boat models I'm familiar with that have wing mounted engines (on high wing locations) use zero-zero thrust lines. (Catalina, PBM Mariner, CL-215, etc.) Because of this, they all fly nice and straight once airborne. On the water, they all want to bury the bow when you throttle up, but because they all have the horizontal stab in line with the props, a little up elevator counters that tendency and they plane up real nice.