Hi! I am planning to purchase 2-stroke 15HP Yamaha outboard engine for an
inflatable boat (3.4 meters, 64 kg). Most of the time I will be driving
the boat alone in very calm sey with just a few spearguns in it. The
engine comes with 9 1/4 X 8 in. 3-blade propeller. Should I purchase a
propeller with 10-inch pitch instead since the load on the engine is
pretty light?

The best way to select a prop is trial on the boat the engine will be on.
Try it first and see.

"Marko" wrote in message
news
Hi! I am planning to purchase 2-stroke 15HP Yamaha outboard engine for an
inflatable boat (3.4 meters, 64 kg). Most of the time I will be driving
the boat alone in very calm sey with just a few spearguns in it. The
engine comes with 9 1/4 X 8 in. 3-blade propeller. Should I purchase a
propeller with 10-inch pitch instead since the load on the engine is
pretty light?

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.