Are the 777 motors more powerful than a 540? If so you have not got a springer you have a submarine. My springers have 540 motors in them and at full power they will dive, even with the batteries set towards the stern.
At full power I have had about an inch of water pouring over the front of the springer and getting deeper. You might want to consider smaller motors, also do not forget to build a coaming around the opening in your deck mine is 25mm high all round and sealed to the superstructure.