When a Prop-Shop alters Prop Pitch........

[SeaKaye12]

Hi,

When prop-shops alter a prop's pitch, is there some typical way that they mark the prop to indicate what changes were made?

Here's what prompts the question:

I have a 1977 Mercury 850 on a rather heavy 16' Tri-Hull. When I first got the combo a couple of years ago; it had no prop (stolen...) So; I purchased a 17P Prop (48-32264-17) from a respected poster here and have been running it. However, even with just me in the boat...I could only get about 5200 RPM WOT. So; last spring I purchased (on e-bay) a 15P prop (48-32390A3-15) Oddly; with that one on there...I can't get past 5000.

Maybe the 15P is not really a 15P??? When I got it; it had a sticker on it indicating that it had been rebuilt/repaired by a prop-shop.

Anyone have any comment? I guess that someday I should quit using junk props and buy something new that cab be properly identified.

Thanks for reading, Chuck

 

[rndn]

Re: When a Prop-Shop alters Prop Pitch........

You can take the prop to a good prop shop and they can tell you what pitch you have. It is possible that if the props are from 2 different mfg's you could get the numbers you discuss while both props are at the stamped pitch.

 

[steelespike]

Re: When a Prop-Shop alters Prop Pitch........

While it is obvious the props are producing different numbers; without speed numbers you can't tell to much.The "15" could be more efficient producing better speed.Of course you would still need to get the motor closer to its rated max rpm.Have fine tuned your setup?Especially vertical height?

 

[SeaKaye12]

Re: When a Prop-Shop alters Prop Pitch........

Speed seems to be about the same; I thought hole shot was better with the 15, but it could just be my imagination.

The boat has some other issues; even with the trim-tab (anode) set to the full right position...the boat pulls to the right.

Is it a big deal for a prop shop to tell me the pitch of both props? ie....is it something they would likely do for free?

It's not that I'm cheap or that the budget's **that** tight...I just hate to keep dumping more money into props that have seen their better days.

Chuck

PS....another poster mentioned a prop "pitch tester".....can anyone show me a picture of one?

 

[walleyehed]

Re: When a Prop-Shop alters Prop Pitch........

A Prop protractor takes some learning to know how to use it....
The repaired prop, I'd guess, Has larger blade area and likely a higher diameter, but who knows what pitch blocks were used to re-align the blades during repair??? I don't mean what pitch, I mean what manufacture the blocks were designed for. If that shop had blocks for an OMC 391198, but the prop is a Merc, it's not going to perform as the original prop did....it'll be more like the OMC prop that the blocks were made for.
I've said this many times, but as an example, I found a 15P SS that would out-run any other SS prop I ran....in a 17P! The 15P pulled the same rpm but was nearly 3mph faster on top.......it's all in the design and sometimes that pitch number is just a reference to be used in the same style/class of props.

 

[45Auto]

Re: When a Prop-Shop alters Prop Pitch........

The boat has some other issues; even with the trim-tab (anode) set to the full right position...the boat pulls to the right.

Real common to see trim tabs set the opposite way from what they need to be. Which side of your trim tab is closest to the right side of the boat, the front or back? The trim tab should be angled like it was a minature rudder trying to turn the boat to the RIGHT if it is pulling right.

 

[walleyehed]

Re: When a Prop-Shop alters Prop Pitch........

Actually, if looking from the rear, the rear of the tab should be right of center...forcing the drive to the Left.....unless we have a counter rotator.