Info required on props

[Nomad NZ]

I have a 45hp Chrysler which i have just rebuilt and have the choice of two props<br />One is a ten and quarter by eleven and the other is ten and three eight by twelve and a half.<br />What prop to use and what sort of preformance can i expect from each one.<br />I run a twelve and a half foot runabout fibreglass over ply.

 

[steverino]

Re: Info required on props

From what I been told, the "correct" prop is the one that allows your motor to rev to the manufacturer's specification for wide open throttle. For example, if the manufacturer specifies a wide open throttle rpm of 5,000rpm - 5,500rpm, that is what your motor should turn when wide open. Too large of a prop is a major cause of engine failure because it makes your engine lug (work too hard). The only way to do this is with a tachometer and test driving your boat with different props. Of course you have to have your boat loaded as you intend to use it.

 

[SeaDawg]

Re: Info required on props

I agree with steverino.<br /><br />However, from just doing some recent prop tests on my boat, my "gut feel" is both of the props are not enough pitch. (I have a 50 HP on a 17 ft. aluminum flatbottom, and I ended up with a 15 pitch SS.<br /><br />So, I would start with the last one mentioned, and see how many RPMs your engine turns.

 

[Nomad NZ]

Re: Info required on props

thanks for the info guys <br />i think i will just try them out on the water and see what happens

 

[novacane]

Re: Info required on props

yep its like rear axle gears in your automble