Evinrude Prop Issues

[brett3600]

I'm new to the forum and appreciate any input given.

I bought a 23' Sunbird Neptune CC about 2 years ago. It has a 97' 200 hp Evinrude Ocean Pro with a 19 pitch (14.5 diameter) OMC Viper Prop. With a light load (quarter tank, one person, no gear), my WOT is 5300 and my speed is 46 mph. The OMC manual says that the max rpm range is 5000 - 6000, so I am within the range. However, the manual also says "the correct propeller for your boat, under normal load conditions, will allow the engine to run near the midpoint of the RPM operating range at full throttle." I'm not sure what "near" means. Anyway, after reading this, I started trying other props. I first tried a 17 pitch OMC SST (14 3/4 diameter), which gave me only 100 more RPM - 5400 (I thought this was strange). The top speed remained roughly the same - 45 mph. I also tried a 15 pitch aluminum prop - that put me at 5600, but my top speed dropped to an unacceptable 37 mph.

What should I do? The motor runs great and strong. The compression is good (ranges from 98 to 110 - in spec according to the manual). I like my speed and performance with the 19 and 17 props (not the 15). Should I be concerned that I am "lugging" the motor? I question this based on some of the things I have read on forums and the above quote from the manual. [As an aside, I do think the manual is poorly written. How can they give a max range of 5000-6000 and then say that it should be "near" the midpoint. Why not just say 5500 and leave it at that]

Thanks in advance!

 

[junior1113]

Re: Evinrude Prop Issues

i have a 93 200 ocean pro on a 21' deep v. running a 4blade 17 pitch @6000= 48 mph. you want to run that motor as close to 6000 as possible. i would work on setup first where is cavitation plate in relation to bottom of hull. with a straight line off the hull cavitation plate should be 1-2 inches higher. honestly think 17 is where u need to be

 

[Texasmark]

Re: Evinrude Prop Issues

If you look at the power curve on engines, taking OMC for example, they say xxxx-yyyy. If you look at the curve, max power is half way between. So on either side you loose a little.

Most of the old salts and my humble self feel that 2 cycle engines do not like to be lugged; course I don't know of any engine that likes to be lugged unless it is a lugger......1000 rpm stroke 1.5 to 2x bore type of thing.
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No two props are the same. The best you can do is to take a brand name and type and if you tweak the pitch an inch or two you have apples and apples. Anything else is apples and oranges.
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You cannot compare an alum prop to a SS period. Main reason is blade thickness. If you don't think that matters, take a baseball bat and swing it through the water then take a machete with the blade at the correct angle to slice the water, and swing it through the water. Alum blades have to be thick to resist the torque because they aren't as strong as SS. Also, SS props are usually high performance so there are other goodies involved.

For what you said, and that is all that I know, run some Sea Foam in the fuel and don't worry about it. The Sea Foam will keep your cylinders clean so that any fouling that MIGHT occur from where you are running your engine will get washed out. Directions are on the can and any quality auto parts store stocks it.

Mark

 

[brett3600]

Re: Evinrude Prop Issues

Thanks guys. I'll check my cavitation plate level tomorrow.