Good after noon friends..i am willing to post one of my experience here...i also was in a struggle, to make a faster craft..so tried many motors and batteries, some even without any ESC.making an esc is not a matter today,as you can simply make an ESC with IC NE555,as PWM oscillator, and its output can fed to BUZ type, or IRFZ type mosfets, can handle ample of currents as you increases the number of mosfets in your circuits.almost one power mosfet can handle 30 amps almost, so a bridged 6 mosfets can do the job nicely.but any how you will lost your battery instantly...
So i turned to an alternate..i purchased a small chainsaw, equipped with a small 35 CC petrol two stroke engine, forced air cooled,pull starter, and it totally weight only 245 grams,include all CDI and Ignition coil.and its size was only just larger than a cycle dynamo.it pumps out around 2.3 bhp, at 16000 rpm,and we won the gold medal last year, as our intern competition was held up...it was based on pure petrol, and a little 2T oil...tidy...exhaust was concealed within the ABS cover...it works even now, and theres no any trouble. speed radar, in our institute shows it simply cruises more than 76 kmph on salt water. at first the prop was the problem to me as the craft speeds up, the cavitation destroys the prop..so i contacted a naval engineering firm and they made a prop for me, a three bladed stainless steel one..so you can try with some engine like that, or can go for engines found in agriculture sprayers..its so cheap to run and extremely reliable..cool