So I made a replica of a unique Canadian amphibious plane, the TR-1 Trigull:
https://www.simpleplanes.com/a/m1Dw95/Trident-TR-1-Trigull

It takes off and lands easily on firm ground and if you are carefull it can also land in water.
But it's not able to make a water takeoff.
After hours of modifying mass and buoyancy values I gave up and present you this challenge: Can you make this plane able to perform water takeoffs without changing the shape of the plane (because it's a replica)?