Craigslist Deal.. or is it?

[jennis9]

We have a merc I/O 140 - and the prop is a 19 pitch.

I am not familiar with this - and apologize for posting before researching. BUT I found a great deal ona prop for our Merc for $50. It is in perfect condition - but it is a 21 or 23. We do not have trim tabs on the transom.

The guy said we could buy it and then if it wasn't to our liking - he'd take it back. Great deal.

What will we notice on a 20' Aluminum Starcraft Openbow?

Thanks i advance. I want to get a deal, but am not sure what I am looking for.

 

[Irv964]

Re: Craigslist Deal.. or is it?

Is it the right size, have the same number of splines etc? I would do your homework first or it just maybe $50.00 dollars wasted?.....My 2 coppers......Irv

 

[jennis9]

Re: Craigslist Deal.. or is it?

I should have elaborated. Yes it is the right size for our motor. we fish alot - have a kicker for that.

what is the number for? what difference does it make? what will I notice?

 

[codertimt]

Re: Craigslist Deal.. or is it?

Any particular reason you're wanting to make a change? How is the performance with the current prop?

I really suggest researching some of this info as you'll get a much better explanation than a short forum post...google "prop pitch" and you'll probably find more thatn you'll ever want to know. But in short, the 21 or 23 number is referring to the pitch of the prop. It refers to the number of inches of forward travel through the water per rotation of the prop. Generally, bigger numbers mean slower hole shot, but more top speed and lower numbers mean better hole shot and less top speed. That is assuming you have enough HP to turn the prop efficiently. You want to have a prop that allows you're engine to rev to it's maximum rpm at WOT....otherwise you're putting extra load on the engine at all points through the rpm range.

Now for you're specific scenario, I personally think a 21" prop will be too much for a 140HP 20 footer. It will be slow to plane, won't reach maximum rpms and generally be bad for the motor. If it's a 23, then it's definitely too big. Having performance numbers from your current setup would help in making an assessment. But if I'm just guessing, I would say it's not the prop for you...

 

[John_S]

Re: Craigslist Deal.. or is it?

I agree with codertimt. Only if you are very under propped now, would a 21 or 23 pitch be fine. That is unlikely on a 20' w/3.0L. If you do not know if you are under propped, pass untill you know for sure.

 

[steelespike]

Re: Craigslist Deal.. or is it?

You shouldn't make any prop changes without a tach reading and GPS speed.
your present max rpm and speed will tell you/us where you are at.
Indiscriminate prop changing can result in premature engine failure from being under or over propped,not to mention poor performance.

 

[Silvertip]

Re: Craigslist Deal.. or is it?

The prop is the transmission for your boat -- and unlike a car, it has only one gear. Therefore the prop must get you out of the hole and allow the engine to operate in the manufacturers wide open throttle (WOT) rpm band. For your engine I believe that's 4600 RPM. If you observe the engine operating higher than that with an average load, then a 21 pitch may be ok but that engine does not have enough power to pull a 23P. In fact, on your boat I doubt it has enough power for the 21P either. If the prop is wrong at WOT it is wrong at any RPM. In your case, installing either of those props would likely result in lugging the engine, you would need more throttle to make up for the mismatch, you burn more fuel, and engine longevity will be sacrificed. So the long and short of this is to make some wide open throttle runs noting WOT rpm. I think you'll find your existing prop is what you need. Speed is not important as what you get in that respect will be determined by the prop that gets the engine to the upper end of its rpm band.

 

[jennis9]

Re: Craigslist Deal.. or is it?

IT ALL MAKES SENSE NOW... I thought the pitch added power, but we really don't need to overload the motor. didn't figure that out until you explained it.

Originally I asked because our current 19 is in need of repair. I have a spare 19, and thought it would be good to replace the original one instead of retool it if this one would work for us. Looks like I want to stay clear of the higher number.

I'll read up a little bit on this topic as suggested, just so I know a little more for the future.

For now, I am going to keep with 19s and have a 19 spare (our boat came with both)

Thanks!