2007 115 Evinrude ETec low rpm @ WOT

[mralda]

Hello, I have a 2008 Zodiac Pro Open 650 (21'4") with a 2007 Evinrude e-tec 115 with 140 hours. My guesstimate is that boat and motor weigh about 1700 pounds and our usual load is 2 adults, 2 teenagers and 40 gallons of fuel (I'd say about 825 pounds). The boat came with an aluminum, 3 bladed prop (14.5 x 21) and it barely got to 4500 rpm at wot. According to the engine manual, recommended rpm range is 5500 to 6000. I just installed a ProPulse composite, 4 bladed prop (14 x 15). I am getting 5400 rpm at wot, acceleration is amazing but speed dropped down dramatically, especially @ cruise (24 mph at 3000 vs. 19 mph at 3500). Should I go down to 14 x 14 to get the extra rpm at wot? What damage is done to the engine when running a prop that doesn't get you into the recommended range at wot? We basically never run the boat at wot and our preferred cruise rpm is 3000 (less engine noise). Thanks for your replies.

 

[steelespike]

Re: 2007 115 Evinrude ETec low rpm @ WOT

You can run at any rpm that suits you but the motor needs to be able to
run in its rpm ramge at wot.Its easier on the motor to be able to freely rev.
Generally a 4 blade will reduce max speed somewhat. When you change material you create more variables as well.If you have no venting(cavitation) issues you probably can raise the motor.
You should check your setup.Antivent(cavitation)plate (just above prop)even with the bottom of the boat is considered a starting point.Raise the motor a hole at a time to a point just before venting becomes a problem.
A 15" pitch Turning point Hustler prop should outperform both your other props.ss performance at aluminum prices.And allow raising motor higher.

 

[Bifflefan]

Re: 2007 115 Evinrude ETec low rpm @ WOT

The boat came with an aluminum, 3 bladed prop (14.5 x 21) and it barely got to 4500 rpm at wot. According to the engine manual, recommended rpm range is 5500 to 6000. I just installed a ProPulse composite, 4 bladed prop (14 x 15). I am getting 5400 rpm at wot, acceleration is amazing but speed dropped down dramatically,

Id say it would, 6p is a dramatic change!! Id say trying a (X)x19p or (X)x17p at the lowest. I'd like to trade you for the 14x15p but its the wrong kind for my motor.
In a prefect world by making that change you lost 6" of travel for every rev of the motor. Thats 16,200 feet every minute you are running at 5400 RPM's. If i did the math right.

 

[Runaway_Alumacraft]

Re: 2007 115 Evinrude ETec low rpm @ WOT

The 115 ETEC should be propped to run ideally in the 5500 - 5600 rpm range with your normal load. The attached site has all the specs you may be looking for http://www.etecownersgroup.com/ ,

 

[mralda]

Re: 2007 115 Evinrude ETec low rpm @ WOT

Thanks to all for your replies. I thought 6p would be a lot... but I'm still not able to run recommended rpm @ wot, think I'm going to need an extra inch. Funny thing is that the boat would plane very fast on the 21p... since it is a very light boat! Only trouble I ever saw was trying to pull me out on a slalom! I am probably going to try raising the engine a little this weekend, I'll keep you posted.

 

[hwsiii]

Re: 2007 115 Evinrude ETec low rpm @ WOT

Mralda, when you changed from a 21" pitch to a 15" pitch you should have gained right at 1,800 RPM minus lets say 300 RPM for the 4th blade. Which means you should have been able to turn 6,000 RPM with the 15" pitch, I think you probably adjusted the pitch wrong on the propulse, or they have the wrong blade angle formula, when you set it since you are only getting 5,400 RPM.

Prop Change

I show the Etec 115 engine recommended WOT RPM to be between 5,500 to 6,000 RPM with a gear ratio of 2:1. If this is wrong then everything I say after this is wrong. Please verify this.

When I run the numbers for prop slip using your 19 MPH at 3,500 RPM with a 15" prop I show that you have a prop slip of 24%.

Prop Slip

If you would run the boat at WOT RPM with the 15" and the 21" pitch props and give me the RPM and MPH I can see better what is happening and can probably help you resolve your problem.
I do believe though that your motor is not as high as you can get it and that will affect your top speed, RPM and prop slip. If you could take pictures level with the anti ventilation plate from the side and the back we can probably see if it is the right height though.
Biffle, he had the 21" pitch turning at 4.500 RPM and the 15" turning 5,400 RPM. 4,500 RPM x 21"/ 12" to a foot = 7,875 feet / 2 Gear ratio = 3,937.5 feet per minute or 44 MPH. With the 15", 5,400 RPM x 15"/12" to a foot = 6,750 feet / 2 gear ratio = 3,375 feet per minute or 38 MPH. 3,937.5' - 3,375' = 562.5' per minute difference or 6 MPH if there is no prop slip, which there always is, just a question of how much.


H