# Propeller options on 15hp Mercury 2 stroke



## DJ Thompson

Hey guys, first post on the thread and many to come. I have a 13' fiberglass skiff i rebuilt from a salvage boat. My old neighbor gave it to me a while ago and i put lots of glass work and paint into it. I have a 1996 Mercury 2 stroke outboard powering it. It is a manual start tiller. I am currently running the propeller it came with 9 1/4 diameter x 9 pitch. The boat tops out at around 22-23 by myself. It has plenty of holeshot for myself, but with 2 people it has slightly less (not a big deal but wouldnt want to lose much more). The current propeller is very chewed up and i was wondering if a 9 1/4 x 10" pitch would be a good option? How much speed would i gain with the 1" extra pitch? Is stainless steel worth it? (I like the idea of stainless and its only about ~$40 more) (and my prop now is veryy chewed up).


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## Skiff Junky

Best all round prop for that motor is the OEM 9 x 9 that the motor comes with. You can get an aftermarket with the same specs.

Going up to a 10 pitch will hurt your hole shot with a load. I run an 8 pitch OEM if I know I'm going to run heavy.

IMHO, Stainless is not worth the money. I saw no significant difference with a 3 blade 9 x 9 with the same blade design but it looks cool.

I run a custom 4 blade stainless 9 x 8 but again, IMHO it's not worth the time, effort and $$$$ for the difference in performance.

Just my .00002563 sense.

SJ


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## DJ Thompson

Thanks skiff junky, so you think just an aluminum 3 blade 9 pitch?


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## Skiff Junky

DJ Thompson said:


> Thanks skiff junky, so you think just an aluminum 3 blade 9 pitch?


Or 8 pitch. Only way to be sure is to tach the motor.

If your only losing "a little " top end and hole shot is good with two people, a 9 x 9 OEM will probably do the trick. If you find it sluggish with a load, it makes a great backup and you can try a 9 x 8 3 blade AL


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## DJ Thompson

Ok thanks alot! How much speed will i lose going from a 9 pitch 3 blade to an 8 pitch 3 blade? Just down 1" pitch


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## Skiff Junky

DJ Thompson said:


> Ok thanks alot! How much speed will i lose going from a 9 pitch 3 blade to an 8 pitch 3 blade? Just down 1" pitch


You may gain speed.

Without taching your motor Im just relaying my experience. I know that motor pretty well.

Pitch is inches forward motion per revolution. HP is rated a a certain RPM. If you are not developing over 5000 rpm due to too much pitch, you will never develop your potential 15 HP. If you drop the pitch 1" and spin over 5500 RPM you will develop the 15 HP and spinning over 500 inches per min faster. Do the math.

Or cheat and play with this: http://www.mercuryracing.com/prop-slip-calculator/

Edit: Sorry the above is a prop slip calculator. If your not confused, it will put you on your way.

This is Mercury's prop calculator but I have never found it to be accurate for Micro's: https://www.mercurymarine.com/en/us/propellers/selector/#/step-five

Trying to find you a prop speed calculator that does the math for you.

SJ

Here: Plug in 10 pitch @ 4500 rpm, 9 pitch @ 5000 rpm and 8 pitch @ 5500 rpm and you'll get the idea. Then plug in the 9 pitch @ 4500 rpm (not maiking 15 hp) and the 8 pitch @ 6K. You want that motor to spin @ 6K (making the full 15 hp).

http://www.rcpro.org/rccalc/PitchSpeed.aspx


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## DJ Thompson

So what is optimal rpm? Its a 1996 mercury 2 stoke 15hp, it weighs 75lbs.


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## Skiff Junky

DJ Thompson said:


> So what is optimal rpm? Its a 1996 mercury 2 stoke 15hp, it weighs 75lbs.


Everything you need to know and then some:

http://www.baads.org/wp-cms/wp-content/uploads/2013/10/Mercury_2-stroke_manual_PART1.pdf

WOT is 5000-6000 rpm. Sticker on the side of the motor should confirm this. I shoot for 6100 with a light load.


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