# prop help, 40 Mercury 4 stroke...?



## Alan in GA (Aug 25, 2010)

Anyone running an aluminum G3 or Triton or similar 16' boat with a Merc 40 4 stroke? What prop are you running and what rpm or speed are you getting?
Never had a 4 stroke outboard but it 'sounds' like I'm running too much pitch with this 13 x 26 prop. It's a package deal so one would think the factory would know "the" prop to install. I've not got an 'ear' for this 4 stroke and VERY QUIET motor but I'm almost sure it's not running the 5500 to 6000 rpm it's supposed to. Top speed w/2 adults is 28.3 mph per GPS.
Thanks for any info!

I'm getting old..what does 13 x 26 mean? I'm sure it's a 13 pitch but is the '26' a blade square inch of surface or what? 
I guess only your tachometer knows for sure! ha!


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## Troutman3000 (Aug 25, 2010)

You can buy a tiny tach for about 50 bucks and test the rpms yourself to see exactly where you are at.


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## Backlasher82 (Aug 25, 2010)

Alan in GA said:


> I'm getting old..what does 13 x 26 mean? I'm sure it's a 13 pitch but is the '26' a blade square inch of surface or what?
> I guess only your tachometer knows for sure! ha!



The 13 is the diameter of the prop, as in 13".

The 26 is the pitch of the prop, sort of like the pitch on screw threads. In other words, theoretically, the prop would move forward 26 inches in one revolution. Of course the theoretical part doesn't take into account the slippage that occurs as it goes through the water but you get the idea.

It's just my opinion so take it for what it's worth but that sounds like way too big a prop for a 40hp motor. For comparison, I have a 14 1/2" X 24 on my 150.

The advise on getting a tach and checking your RPMS is spot on, you need to know for sure what RPMs you're turning before you can go much further.


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## Alan in GA (Aug 25, 2010)

*I don't think so...*



Backlasher82 said:


> The 13 is the diameter of the prop, as in 13".
> 
> The 26 is the pitch of the prop, sort of like the pitch on screw threads. In other words, theoretically, the prop would move forward 26 inches in one revolution. Of course the theoretical part doesn't take into account the slippage that occurs as it goes through the water but you get the idea.
> 
> ...



It is a 13 pitch, not a 26. I think they've used a different type of prop description on this prop. The 13 x 26 is a sticker on the motor right above the prop. The last 3 digits on the prop hub are 'P13' and I know the 35 to 50 hsp range usually run 10-15 pitch. I'm not sure WHAT this means.
Your description is one way commonly used to describe props but this seems different. I'll call the Merc shop now and find out just what it means. I could be wrong!


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## Alan in GA (Aug 25, 2010)

*OK, form the Mercury dealer....*

He said even he does not know what the number means. The 2.00:1 is the gear ratio but does not know what the other means. I could guess it's a 26 spline shaft??? : ).
He explained that the 4 strokes are slower out of the hole and take longer to 'wind up' unless one has one of the super charged engines [verado?].
I'll get a tach, get a tach, get a tack....but, it could be that my buddy weighs more than I thought he did! ha!
I should have made a speed run by myself but forgot to do that.


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## RockyS (Aug 25, 2010)

I think Backlasher is right.  My 1860 tracker will run 30-31 on gps with 2 people a 40gal bait tank and this is with a 75 optimax.  I think mine has too much drag in the water and not enough prop.  It will however jump out of the hole pretty hard.  I was told a lot of people prefer this in a river boat as it puts you on plane faster so you dont have as much time to hit bottom in a shallow river.  If that makes sense.


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## puddle jumper (Aug 25, 2010)

Are you sure thats not a 16x13p??? Sounds closer for your boat...
and here is a web site to help you with the size you need...
Ive got a 50hp merc. two stroke and running a 10x13P on a loaded 17ft triton...and I get 34mph
PJ
http://www.propellerwizard.com/help_engine.php?locationID=55


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## Fishlipps Revisited (Aug 25, 2010)

i've got a 16' aluminum boat....and i run a 40 merc 2 stroke.....with a 14 pitch SS prop......when i set the boat up, i borrowed a shop tach, and i was turning about 5500 rpms @ WOT....and, i carry a LOT of stuff in my boat....top speed about 36 mph..

and, this may help...

http://www.go2marine.com/productcenters/propellers/propeller_fit_guide.shtml


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## hipster dufus (Aug 25, 2010)

is this the triton stick steer? u beat me to it, i was working momma around to the idea of a new boat. good luck, let me know how u like it, top speed etc. i have a tiny tach on my jons outboard, the one with the resetable hour meter.it works fine. i also need to reprop my little 9.8 4 stroke to get my rpms up. still doing research. check out the iboats forums, they have one dedicated to props.


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## Alan in GA (Aug 25, 2010)

*How many in the boat?*



Fishlipps Revisited said:


> i've got a 16' aluminum boat....and i run a 40 merc 2 stroke.....with a 14 pitch SS prop......when i set the boat up, i borrowed a shop tach, and i was turning about 5500 rpms @ WOT....and, i carry a LOT of stuff in my boat....top speed about 36 mph..
> 
> and, this may help...
> 
> http://www.go2marine.com/productcenters/propellers/propeller_fit_guide.shtml



Is that with one or two aboard?


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## sinclair1 (Aug 25, 2010)

Alan in GA said:


> Is that with one or two aboard?


There is a formula out there ......Fishlipps stuff= one passenger


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## Fishlipps Revisited (Aug 25, 2010)

Alan in GA said:


> Is that with one or two aboard?



just me.....but, i go about 260...


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## Fishlipps Revisited (Aug 25, 2010)

sinclair1 said:


> There is a formula out there ......Fishlipps stuff= one passenger



i can't deny that.....


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## Backlasher82 (Aug 26, 2010)

Alan in GA said:


> It is a 13 pitch, not a 26. I think they've used a different type of prop description on this prop. The 13 x 26 is a sticker on the motor right above the prop. The last 3 digits on the prop hub are 'P13' and I know the 35 to 50 hsp range usually run 10-15 pitch. I'm not sure WHAT this means.



A 13" pitch sounds much more reasonable on a 40hp motor, but I'll bet a dollar to a donut that it isn't 26" in diameter.

Somewhere on the prop it should have the diameter and pitch stamped into the prop. Sometimes it is stamped between the blades, sometimes inside the hub so it could be covered with exhaust soot but all props are referred to by diameter and pitch.


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## Alan in GA (Aug 27, 2010)

*label on motor leg...*

here is the label that even the Merc machanic said he didn't know what it meant:


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## puddle jumper (Aug 27, 2010)

You need to pull the prop and look for this on the hub  of the prop not the motor...
Here is my old one from my 50..

PJ


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## Alan in GA (Aug 27, 2010)

*prop ID..*

There is also a part number on the outer hub. Guess I could look it up.
A tach is the answer reguardless of the prop's id I guess.


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## ribber (Aug 27, 2010)

prop pitch and diameter will be on the prop. 13x26 is the gear ratio in the lower unit. not sure about the 4 stroke mercury but a 2 stroke 40 should be running a 10x13 or 10x14 prop.


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## Alan in GA (Aug 27, 2010)

*that makes sense....*

13 x 26 is 2:1 ratio. Didn't 'see that'... : )


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