What's the difference?(Prop question)

[bluegillfisher]

I have an old 9 1/4" x 11 prop on my boat. The new one is 9" x 10. How will the new prop change the way my boat drives. Is it
a big difference and I should keep looking for one the same as old one( which is fine, but bent and nicked and looking really old).
The dealer said the 9x10 was what Johnson put on the new motors. I have a 14foot by 48" jon boat that I use on small lakes. The motor is a '74
Johnson 25 horse.

 

[Johny25]

A 9X10 is most likely going to run your motor at too high an RPM. With the drop in pitch and diameter your likely to go up 250rpm. Do you have a tachometer? If not then I would invest in one if you want the correct prop for your setup. You want your RPM's to be at around 5500 give or take 100. If you stick that 9X10 on and end up over 6000 then you are going to put unnecessary wear on your motor, along with other possible bad things like engine seizing [-X

The lower the pitch the better the holeshot, higher pitch for top speed. So if you drop in pitch you will gain holeshot and lose some top speed on your boat. But I would really advise getting a tiny tach for around $50 so you can get the perfect prop for your motor and needs.

 

[bluegillfisher]

I have thought about a tiny-tach. I start looking for the same size prop as is on it now, but I think your right about getting a tiny-tach first.

 

[Johny25]

Yeah if your prop can be salvaged by filing the burrs and dings off then I would hold out for a tach so you can get a prop that will ensure your engine runs at the correct RPM. The $50 for a tach is a lot cheaper than a new motor or even buying a couple props untill you get it right.

I just looked your motor up and it looks like the stock prop in 74' on the 25hp was a 9X10 but if you are running a light setup then you may want to stick with the 9.25X11

 

[Buddychrist]

Have you thought about having your prop cupped?