Serious Prop Question

[cougar166]

Okay, I recently purchased my first boat (dad and brother had one so it is now my turn). It is a 1989 Starcraft with a 150hp Evinrude. The prop is a 3 blade aluminum with a bunch of nicks and gouges in it. The boat goes nice (45mph ((gps)) @ approx. 4300 RPM) but I would like to get a new prop. I have no idea where to turn as the local places all tell me something different. I do not want stainless as I mostly go on inland lakes, but am interested in a composite prop.

Any advise? Thanks in advance ~Chris

 

[studlymandingo]

Re: Serious Prop Question

What is your speed and RPM at WOT?​

 

[Esox]

Re: Serious Prop Question

Before you buy a new prop you need to verify the tach is accurate. If your only running 4300RPM at WOT you are seriously lugging that engine and it will have a very short life. Without knowing the pitch of the prop we can't run the numbers in a prop calculator which will shed some light on things.​

 

[rndn]

Re: Serious Prop Question

A question? Is there anyway to measure a prop that has no markings on it to tell me the pitch?

 

[walleyehed]

Re: Serious Prop Question

Used to be able to measure the blade attach perpendicular to the hub and multiply by the number of blds, but since progressive pitch and other cupping factors have come into play, this measurement isn't as accurate.
There are numbers either between the blades or on the inner hub under the nut and washer.

 

[cougar166]

Re: Serious Prop Question

Okay, the prop that is on there now is a 14-1/2x19. I went out over the 4th and the speed was about 45mph at 4700 rpm's at WOT with trim at 1/2.

 

[walleyehed]

Re: Serious Prop Question

That figures out to about 4.5% slip....I don't think that's possible on this rig, which brings me back to the tach...I'm sure we have some issues there..it NEEDS to be verified. Even if the tach was correct (it's not) you are about 800-1000RPM low. We need to know actual RPM before we waist any time propping with a bogus tach

 

[cougar166]

Re: Serious Prop Question

So what do I do next?

 

[studlymandingo]

Re: Serious Prop Question

You need to get the tachometer checked out and repaired if it is off (which it seems to be if that is your WOT with that prop).​