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Currently have a 10.5 X 11pitch.

Boat will do about 22 mph WOT (GPS) jumps to plane fast have no idea what my RPMs are.

Motor has been fully serviced and runs great.

I see posts saying that a 13 classic should do close to 30mph with a 25hp.

The whaler has to be able to keep up with the 25 MPH cruise speed of my Cruisers 3370.

Need to know what prop to go to. Choices appear to be

10 X 13 pitch
10 X 15 pitch.

If anyone has experience with this set up I sure could use some advice, motor is one or two years after the HP rating went to the prop.

Whaler is a 74 13ft.


Thanks in advance for any help.

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If those are the choices, you'll want the 13" pitch.

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OK, found out engine is a 1991. Put on a 10 X 13 prop. this is the midsize prop for this engine. Diameter on all props 13 pitch and up at 10". I can tell the engine is doing fewer RPMs be the sound. However, I am not getting any increase in top end. Both the 10.5 X 11 and the 10 X 13 top out at 22 mph.

I cannot find a 9 X 13 for this year of engine.

the boat is a 1974 Sport 13. Weight is 360 spec. we are at about 430 with full gas tank and battery (I use a jet ski battery so the wight is about 1/4 of a standard battery. boat sits just right in the water. waterline about 1" below the free board chine.

Any ideas would be appreciated

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I've said this before on many questions about props.....

We do not buy props by diameter. The engineers take care of the diameter according to the pitch for the motor(s) the prop fits...

We buy props from a manufacturer in Pitch only........
I have no idea why everyone gets confused by this....

Here are some of our choices...
13 pitch
14 pitch
15 pitch
16 pitch
17 pitch
etc., etc., etc......

We have to decide what pitch and brand of prop we want to try as some are more aggressive than others. Still, we have No choice in diameter....

If one manufacturers 13 pitch prop is too aggressive, then we can try another manufacturers 13 pitch prop that may be less aggressive or step down to a lesser pitch prop....

Hope this helps.

Your earlier post says the original prop was fine with the correct WOT RPM's and a top speed of 32 mph... Has something changed?
http://www.whalercentral.com/forum/vi...post_69037

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Hey Joe -- I'm still learning about props and what all this means. So, excuse my ignorance, but I'm intrigued by your post. I recently also posted about needed to swap out props b/c my current 9 pitch set up was used on a pontoon boat. With Tom's help, we decided a 14 was about right.

But, is what you're saying that I shouldn't be concerned about the prop's diameter? Just get the right pitch prop and that's all that's important? Been struggling with this b/c I see a prop I'd like to buy bu the diameter is not the same as the prop on my motor now. And, somewhere in my noggin I'm thinking they should be the same. If not, let me know -- and the original poster as well since I think this is very useful info!

Thanks in advance for your advice on this! Again, this is all intriguing to me!

Bruce

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Not wanting to speak for Joe; however I believe he said to find the proper propeller diameter for that engine from the manuals, etc. Then work with pitch, cup, Mfg., blades, etc.
Long ago, I thought I had some understanding of propellers.
About 10 years ago, I found that I was out of the loop. You have a lot of options.
You can also drive yourself into penury for one more mph.
Good Luck!

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What I am saying is "Forget about Diameter"....
Don't think about it, no need to even mention it. It is irrelevant to us.

We don't have that choice... It is already taken care of by the engineers who make the props for a certain motor.

Example:
If you go to buy a prop for a 1985 Evinrude 70 hp, here are your choices.
15 pitch
17 pitch
19 pitch

Who cares about diameter? Only the engineers...
The diameter of the prop is what it is and we can't choose the diameter.
Diameters of props are different for different pitch props but we still don't have a choice in diameter.
This makes it easy for us...
Buy a prop with the correct pitch that you need. If it is too much pitch or too aggressive, then buy a prop with less pitch or less aggressiveness....

Pitch, Pitch, Pitch...

As Boatingnut mentions above.

That's probably because there isn't such a thing for his model and brand of engine.
Again, who cares about diameter? Not us.... we only care about pitch.

So, how are we going to choose a prop?
By the pitch and then the manufacturer or brand of prop.......
Certain pitch props will give stern rise or bow rise and that may be a factor however we still cannot choose the diameter.... Only the pitch....

So, I hope we have forgotten about diameter or does anyone think the diameter is still important to us?

Here is another post about pitch and diameter and diameter lost....
http://www.whalercentral.com/forum/vi...post_66668
Again, all we need to be concerned about is Pitch.... and then the brand....