Any suggestions on prop size

[onthelaketwo]

My current prop is alumnimum marked 14x11

The boat is a 25 foot manitou oasis with 2 toons
The motor is a 90hp evinruide etec

The boat now goes about 22 mph at 4900 RPM @WOT. with 500lb of passangers and full gas tank.

The motor should be able to go up to 5500 RPM.

What would be the suggested prop? I was going to get a new one, and use the current as a backup.

Thanks in advance.

[HandymanHerb]

Here's where a prop shop comes in handy, you get about 200 rpm for every pitch you go down, so your around and 8 pitch, but if you got a shop that will let you take a few to try.

Then you can buy the one you want and they can repitch your old one to match

[big daddy]

same problem with the banana cabana, 24 foot running a 90h.p. etech I go close to 22mph at 4700 w.o.t. I really dont like turning up that high if its w.o.t. but as you stated we are supposed to be in the 5500 area. my prop is a 15x13 so dont buy that size is what i'm trying to say

[hotairgypsy]

i am in the process of installing a tach so i have a clue what my rpms are too so i can figure out the rigth prop size. is there a prop calculator around which could help us out with figuring out what is optimum. i have a 14x13 in my case and i assume i am changing the first number and not the second

[rockymax]

Try powertechpropellers.com. They have a prop worksheet that you can submit for help. They have some very helpful people. Even though your prop may be the significant or only reason for the lower RPM's at WOT, sometimes the improper engine height is a major contributing factor.

[mikeherb]

Here is another good site for props:

http://www.dansdiscountprops.com

[dockholiday]

Seem to me you should be able to turn the 11p prop with 90 hp. Got any idea on the weight of your boat?
doc

[brumbyvet.1044]

I know you have a rude but you might try the mercurymarine.com site. They have a great prop selection tool. It would give you the diameter and pitch and then you could convert that to a evinrude prop. Good luck.

[onthelaketwo]

Boat weighs about 1850lbs plus 320lbs for motor. plus 27 gallons of gas, plus 500lb load during testing.

[dockholiday]

Boat weighs about 1850lbs plus 320lbs for motor. plus 27 gallons of gas, plus 500lb load during testing.

Actually think the wot should be around 5800. Does the above weight take into account the sea legs? Seems like your boat is near in weight to mine just figuring boat and motor. Is that rpm trimmed out as much as you can without blowout? Guess you could drop down a notch in pitch but seems like something else is going on. Have you checked it without the load of gas and cargo to see how it affects the rpm?
doc

[rockymax]

I agree with Doc. You need to make certain that your trim is optimum. Also, is your engine at the correct height. After establishing this, if you have the ability to try a lower pitch prop, this will tell you if the prop pitch is the problem. When you determine the prop pitch you need, buy a Viper prop. This will give you the best rpm and top end speed for you Etec.

[onthelaketwo]

I did not get a chance to work on it yet. Lots of people have told me the 14x11 should be fine.

Maybe my RPM gauge is not reading properly. Any method to check easily?


I am going to reprogram the motor in spring to burn XD100 oil, I guess they can check computer to see top RPM recorded, as it records a histogram of RPM speed.

I guess it is a project for spring.

[Bamby]

Seems a 14x11 should be fine on your boat a lot of folks I know with 90s actually run 14x13s on theirs. If your toons are filthy from a whole summers worth of crud that will both slow you down and effect top rpm performance. Recently I cleaned mine though not that cruddy I picked up almost 300 rpm's and some speed.

[peapenl]

I have the same motor on a 22ft crest and turn 5200rpms with a 14x11