I have a similar boat at 3.6 meters, 72 kg. with inflatable keel. I use
a 15 HP Tohatsu 2 cycle. It came with an 8.5 in. 3 blade prop. as
standard. We plane at 10 MPH with 280 kg (600 lbs.) and can go 20 MPH
top speed. With one person, I am sure 25 MPH would be top speed. Not
sure what your objective is? A new prop can cost $50-150. I agree
with JamesgangNC if you can afford it.