Fun with Props!

[WaltF]

ok.. here goes...

Ive got a 3.0 i/o mercruiser on da toon.
Running a 16x13 Quicksilver AL prop.

Up here in Colorado, between the high altitude and all the FAT people on my toon , i need something less to reach WOT.
There are usually 10+ peeps on my toon.
Even with 2-3 peeps i can only just reach the bottom of WOT, 4400, which is 4400-4800 on my 135hp 3.0.

Im wanting to put a 14x11 on it.

Looking on Dan's prop store site.

They dont offer a 14x11 for the Mercruiser Alpha drive, BUT they do offer it for the Mariner Outboards. 40 to 140 HP.

Is it ok to put a prop made for the OB on my sterndrive if the HP rating is ok? Both require the same Mercury Flo-Torq II hub kit, so i imagine it would fit on the shaft ok...

Otherwise, it seems the 'smallest' prop offered for the 3.0 sterndrives is a 16x11.
Yet, another guy i talked to agreed with the 16x11... he said not to drop the diameter, but just the pitch and go with a 16x11.

Thoughts?

[GXPWeasel]

I'm not sure on the OB or I/O props being the same. Your logic makes sense, and if the shaft is the same, and rated for the same HP, then I don't see why it wouldn't work.

As for the diameter of the prop, I would keep it the same as what the motor came with, or you have now. I would only change the angle, and/or the # of blades.

Maybe look into a 4 blade prop???

[Parasympathetic]

I'm not a prop expert or even close, but methinks a 14 X 11 will put you way past your redline. I think each change in pitch equals 200 rpm. So if you're at 4400 rpm now with a 16 X 13 and change to a 16 X 11, that should put you at the 4800 rpm max.

Here's a good prop site: http://www.propmd.com/t-PropellerBasics.aspx

[Bamby]

Walt,
I'm not that familiar with inboard motors myself. But is your boat motor equipped with fuel injection or carberated engine. If you actually are boating in high enough elevations and it's carberated you might actually need to make some adjustments to the carb. Where Fuel injection motors will monitor and adjust automatically with the elevation. I guess what I'm questioning is weather it's a motor or a prop issue or maybe a bit of both.

[WaltF]

Opps... missed these updates!

It's a carb, so you might have something there!
I'll look into that! Thanks for that thought!

I think ill drop to a 16x11 and get er tuned too. Couldnt hurt!

[slingshot]

Your I/O is swinging a 16 in diameter prop for a reason. That alfa drive is geared low. For every inch you drop in pitch your wot rpms will increase by about 200 but in an alpha maybe a little less due to the gearing. I'll bet that an 11 inch pitch will put you right where you want to be.

[Bryden24shp]

Actually Walt, you can run a smaller diameter prop and same 13 pitch, it will do exactly the same thing your are looking for. The smaller diameter will have more slip to it, and by not grabbing as much water, it will spin faster. My Manitou came with a 15 1/4x17 Apollo from the factory. My fastest prop is 13 3/4X24 Raker and my favorite prop is my 14 1/4X21 Renegade Offshore 4 blade. The biggest thing when playing with props is to take a GPS and a pen & paper to take notes with. If ya had an Etec, I'ld send ya some to try!
Good Luck
Bryan

[WaltF]

Swwet Info once again!
Whelp, i ordered the 16x11 from Dan's Prop's.
100 bucks, hard to beat that guys deals!

[slingshot]

Good call, let us know how it worked out.