# Increase of pitch rule of thumb ?



## Brett (Jul 16, 2008)

http://www.propmd.com/t-propellerbasics.aspx#pit

covers most of what's needed to make an informed decision.


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## Frank_Sebastian (Oct 15, 2007)

If that is the 2 stroke Merc 25 HP that you mentioned in an earlier post and the boat is an aluminum skiff with a light load I would think a 3 X 10 and 3/8" X 13 would be about right for the boat with a light load?

A 9 7/8" X 11 prop would likely be hitting a rev limiter and doesn't sound right for the engine mentioned earlier.

Best regards,
Frank_S


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## fredslann (Oct 14, 2009)

thanks for the info...
It was a yami and I ordered a 10 X 12 solas...at least for now. That's takin it up 3 inches...and sometimes I have a passenger that may go more than 220lbs...but your most likly correct that this prop may also hit the limiter with just me and a light load. 

When I get the new wheel on, Ill post what it did to the topend and RPM's

Thanks


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## Frank_Sebastian (Oct 15, 2007)

There is nothing wrong with under propping a little. Almost every commercial fisherman does it in hopes of a big catch. Then when (and if) you do find yourself with a heavier than expected load you will be able to get it up on a slide (plane) and get home before daylight.

Best regards,
Frank_S


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## fredslann (Oct 14, 2009)

just an update...
added the Solas Alum 9.9X12 and got and avg. speed of 29.5MPH by GPS while taching out @ 6000...1/2 load 4"chop on the water. I had raised the motor up one inch on the transome..it didn't blow out until I put it hard over. I have the moter at the most angle the yoke will allow so the next thing is to see if I can make a wedge so I can get the nose up a tad more...it seems to be running with most of the water coming off at midway of the hull....which is not a flat bottom alum skiff...it does have some V but it does appear to have some hook in the hull bottom at the Transome...that may explain not getting the bow to rise.

But otherwise the prop works nicly!!! I'm pretty happy with that speed!
Thanks foe the help fellas


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## Flyline (Mar 3, 2008)

wow! that 's fast for 9.9hp so can u please please post a pics so we all see the pics!


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## Lil_Tate (Dec 18, 2006)

> wow! that 's fast for 9.9hp so can u please please post a pics so we all see the pics!



it says 25 merc on this thread, does it not?
i dont see where it says 9.9hp anywhere on here?


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## Flyline (Mar 3, 2008)

> > wow! that 's fast for 9.9hp so can u please please post a pics so we all see the pics!
> 
> 
> 
> ...


Ohh... :-[ nope....I guess I read too fast... ;D


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## fredslann (Oct 14, 2009)

Just one more update....
The boat is a 87 Alumacraft...same as the Express boats now...16fter. motor is a 2strk 25hp yammi.
I made a 10 deg wedge to see if that'd help get the nose up and it did...but was squirlley. MPH only increased by 2.. and blowouts took place in the slightest turns. So I took the wedge out and I'll take the gain in speed I first got.


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