Oké Flashman,

There are a number of things to check:

Is the drive train running smooth? No old grease in the propshaft, or no grease at all?

Does the motor rev as high out of the water as in it?

Do you use a prop with sufficient lift?

Have you tried launching the boat with a push, so it's on the plane from the start?

Is the motor running very hot? If it has been doing that for a long time, the magnets will weaken, losing the motor power.

Hydroplanes need a high revving motor, if non of the above works/applies, try a motor with more RPM

What type (mAh) cells did you use, were they freshly charged, or the day before?

See what works for you, the next step would be modding the sponsons and maybe adding a running pad, but in order to advise you on that, I need the pictures I mentioned above.

Greetings, Jan.