Mercruiser 140HP 13.75 x 15 prop for 9000' ?

[fishrdan]

I looking at a 15P prop for my Mercruiser 140HP (2000# boat) while up at 9000', and wondering if a Michigan Wheel Vortex 13.75" x 15P prop will work? Good deal on the prop. The Mercury prop selector says to run a 15.5 x 15 Black Max, but while reading through old posts I've seen replies that say prop diameter really doesn't matter as it's a function of the props design. I have a feeling the 13.75" D prop might blow out (vent, cavitate, whatever the term might be) since there is far less blade surface area than on a 15.5" D prop, and that this 13.75" x 15" prop is designed for outboards opposed to an I/O,,, I could be off my rocker on that though...

I should say, Mercury's prop selector wouldn't go up to 9000', but I entered in a boat that was heavily loaded (extra 1200# above max capacity) at 5000' and it spit out a 15.5 x 15 prop.

I'm guessing at the 15P prop selection as I only run up at that elevation 1-2 times a year and don't have access to RPM and MPH numbers, without driving 6 hours to a frozen lake But, I can say at 9000' with a 17P prop the boat would hang at 2000RPM (15MPH?) struggling to get on plane and then finally break over on plane after 30 seconds or so. I run a 19P prop at 1000' and am very satisfied with the performance.

Is the 13.75 x 15 prop going to be a waste of money and should I buy a 15.5 x 15 or 15 x 15 prop?

(oh yeah, these are all aluminum props)

Thanks, Dan

 

[MRS]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

I had a merc.120 and would run a 15.5x15 for big bear lake worked great but really had to watch the rpms. Plus had to change the trim tab Anode the prop would hit the one that I ran with a 15x17 prop. so watch that. I did buy a composit hub with inner changable props. 17 & 15 pitch blades and would leave in the boat for spare. My regular main prop. was aluminum 15x17. Where are you going that is 9000'?

 

[fishrdan]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

Hey MRS, do you remember the RPM's at cruise, or minimum RPM's to stay on plane? What was your old boat, size and approximate weight if you remember. I go up to Fish Lake, UT which is 8800'. The lake is pretty small, 6 miles, so I'm more concerned with getting on plane quickly, opposed to speed.

 

[MRS]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

Can't be sure it has been awhile since ran that boat with the 15 but I think it curised about 3000rpm. It did rev up real quick thou so I could get on plane fast and just feather back top speed was only maybe 26mph. It was 17ft. thunderbird not sure on weight but was fairly heavy for a 17ft. boat and it only had the 120 4cyl. in it sorry could not help much but I do remember had to watch rpms because it would rev. real fast and like 5400 wot. Not good for a 1969 120 motor.

 

[fishrdan]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

Thanks for the feedback MRS. That sounds about where I thought I would be at, around 3000RPM cruise at 9000' elevation with the 15P prop. I normally cruise at 3300RPM at 1000' so if I can maintain that RPM up at elevation I'll be happy, even if it's slower.

Anyone have comments about 13.75" VS 15.5" diameter for a 15P prop, for an I/O?

 

[Bondo]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

Anyone have comments about 13.75" VS 15.5" diameter for a 15P prop, for an I/O?

Ayuh,... My guess is, the prop in question has a 4" body for the mid-sized gearcase Outboards...
Mounting it on the 4, 1/2" gearcased I/O, it'll immedately Blow out,...
Because of the 1/2" difference where the prop meets the gearcase...

 

[steelespike]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

13.75 thats almost 2 inchs undersize as Bond-o suggests probably intended for an outboard.

 

[fishrdan]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

OoooK, so I was right in thinking this was probably an outboard prop, guess I'm not off my rocker, yet.... I didn't even think about the body diameter being smaller, place selling the prop didn't have applications listed, just Vortex 13.75 x 15 prop.

I'll go looking for the "right" prop now.

Thanks again,
Dan

 

[Silvertip]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

While it is true that prop diameter is a function of "design", that statement means it is a function of design "for the engine it was designed for. As Bond-O pointed out, hub size changes between engine series so just because a prop fits on the prop shaft does not mean it is intended for that outdrive or outboard. You buy a prop for your outdrive. Then within the range of prop pitches for that outdrive you will find that as pitch goes up, prop diameter comes down sllightly and vice-versa.

 

[fishrdan]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

I really appreciate all the good info on prop diameter Bond-O, SS, ST.

That's why I was asking, it didn't sound like it would work to me. The prop diameter didn't sound correct, even though there are higher pitched props that will fit my I/O, with a diameter close to 13.75", it didn't sound right for a 15P prop. Heck, my 19P prop is 15.5", so I was really doubting the smaller diameter 15P would work.

I'm only going to use the 15P prop 1-2 times a year,,, but I guess a "good deal" isn't so good if it wont work

 

[Bondo]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

but I guess a "good deal" isn't so good if it wont work

Ayuh,... Even Free ain't a very Good deal if it don't work......

Even worse, the length of those props are really close to the larger bodied 1s,...
It'll go right on the propshaft like it should, tighten down like it should,...
Even sorta look right, from the right angles...
It'll even Work,... Sorta....
Problem is,... It'll Ventilate, Severely at anything above Idle,... Probably even At idle....

 

[fishrdan]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

Ayuh,... Even Free ain't a very Good deal if it don't work......

Awww, C'mon Bond-o, there's lots of things you can do with a free prop,,, now where's that picture of the prop-planter...

It would look right at home with the rusty anchor in my flower box out front.

 

[Bondo]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

Awww, C'mon Bond-o, there's lots of things you can do with a free prop,,, now where's that picture of the prop-planter...

It would look right at home with the rusty anchor in my flower box out front.

Ayuh,... I concede that I can find a purpose for danm near Anything,...
But,...
Most folks ain't the Packrat I am either....

I've now built a couple of the Prop Plant Pots,...
I'll look,+ see if I've got a shot of 1 of my Prop Trees.....

 

[fishrdan]

Re: Mercruiser 140HP 13.75 x 15 prop for 9000' ?

I'll look,+ see if I've got a shot of 1 of my Prop Trees.....

LOL, Prop Tree,,, I've gotta see that!