9.9 prop pitch suggestion

[Toolbagtyler]

I have a 14 ft aluminum sea nymph 14k which is just an aluminum semi v with an 85 evinrude 9.9.
I believe it has the stock 10 pitch prop and I am getting about 4850 rpm and 14.5 mph with 2 people, 3 gal of gas and 29 group battery. About 5080 rpm 17mph with just me. I will usually be riding with 2 people and added gear. Should I go with with an 8 or 7 pitch? I saw evinrude wot rpm is suppose to be 5000-6000. Thanks.

 

[ktoelke54]

I went through the same process with a 15 hp OMC. In my case I needed to gain about 700 rpm and the choice for me was to go from the standard 10 pitch to an 8 or a 9. I tried the 8 first, it was overkill. It turned out the drop to a nine was right on the money. Between an 8 and a 7 I’d definitely go with the 8.


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[Toolbagtyler]

Thanks. Wonder if I should be looking at an 8 or 9 instead of the 7. How much rpm did you gain from the 9? I was figuring 200 per inch.

 

[ktoelke54]

Thanks. Wonder if I should be looking at an 8 or 9 instead of the 7. How much rpm did you gain from the 9? I was figuring 200 per inch.

I heard that 200 an inch thing also. I’m my case i gained 700 rpm going from 10 to 9. The mathematical difference between the two pitches is over ten percent, a little over 500 rpm. I attribute the remainder of the gain to getting the motor back in its power band. My boat was a fully loaded 1436, maybe a little overloaded, two big guys, trolling motor and battery, etc. The 15hp with a 9 pitch did a good job on this boat. Got the boat up on plane easily and cruised along at 18 mph or so. So with the 14’ boat, with just me in the boat, the 10 worked the best, topped out at 20. Loaded the 9 was the ticket. The 8 was overkill, jumped up on plane, but cut the top speed down to 17, and the motor over-reved, got sold on eBay, most of my $55 bucks or so back.

Another member of this forum had the same result with an OMC 15 2 stroke. He dropped from ten to nine and gained 700 rpm.

If I were you I’d start with the 9 and go from there. I’d be interested in what your experience is either way?


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[Toolbagtyler]

Got the 9 in the mail. Got the solas Amita 3. Not sure when I will get her out but I will update when I do

 

[turbotodd]

200 rpm per inch of pitch "generality" doesn't apply to anything under about 50hp.

 

[Toolbagtyler]

So did some testing this weekend... with just me the 9 pitch was pretty much perfect. Got on plane and topped out at 20.2 mph at 6090 rpm. However with my girlfriend and I I could barely break plane and would stick around 5280 rpm and 15.5 mph. When I occasionally did get on plane after cruising a long time straight I'd get up to 17.5 at 5700 rpm. Being that i wil go with two people most times with more gear and a heavier passenger then my girlfriend should I try an 8 pitch to get on plane quicker? Or maybe a 4 blade? Do you think it will make a difference?

 

[ktoelke54]

Yes, an 8 would handle the heavy load better. I switch props on my boat routinely to adjust for load.


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[GYPSY400]

So did some testing this weekend... with just me the 9 pitch was pretty much perfect. Got on plane and topped out at 20.2 mph at 6090 rpm. However with my girlfriend and I I could barely break plane and would stick around 5280 rpm and 15.5 mph. When I occasionally did get on plane after cruising a long time straight I'd get up to 17.5 at 5700 rpm. Being that i wil go with two people most times with more gear and a heavier passenger then my girlfriend should I try an 8 pitch to get on plane quicker? Or maybe a 4 blade? Do you think it will make a difference?

Sounds like you got your prop pitch as good as its going to get.. now you need to play with weight distribution.
Where is the passenger sitting?
Where do you have the battery placed?

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[Toolbagtyler]

Battery is up front and passenger is in front most seat. Thought about moving passenger to middle seat. Im not getting excessive bow rise. I feel like I'm right on the edge of planing with 2 and onces I get there its great, you can tell the motor isn't working as hard

 

[GYPSY400]

Yeah sounds like the boat is plowing.. you'll need to play around with where the passenger sits , where the battery is, and your trim setting.. unfortunately a 9.9 doesn't have power to spare.

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[Toolbagtyler]

Yeah sounds like the boat is plowing.. you'll need to play around with where the passenger sits , where the battery is, and your trim setting.. unfortunately a 9.9 doesn't have power to spare.

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That's what I will do next outing. I messed with the manual tilt a bunch. I dont think the bow is plowing cause it sits up a little and when I really plow it sprays water everywhere. Maybe I need it lighter up front to pop the rest of the hull up easier. Hopefully it will be as easy as moving the passenger back. Otherwise I'll just have to live with it for now haha

 

[ktoelke54]

Or look into upgrading your 9.9 to a 15. Not to big of a deal with the OMC 2 strokes. Worth looking into.


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