How to increase power ?

Hello,

I just buy a 65121 flipsky's motor and a "Flipsky 75100" ESC. My goal is to make a counter current swimming machine. So i don't use a remote, but a PWM control knob.

I followed some tutorial, and i managed to make it turn, but the current is too low at 95% duty cycle.

Do you know how can i increase that ? 

The perfect case would be to have a amount of current compared to duty cycle. 

Thanks for your reply