Prop Question

[tech62571]

I have a 2006 1800 MX
3.0 with Alpha one Gen 2

Im trying to find out what the original prop is. (make and pitch ect)

It has a quicksilver prop now and I cant read the numbers (looks like 1818e21)

[jrsick]

most likely it was a 19P, 14.5 inch prop. This a good general use prop for your boat. If you're doing a lot of water sports that require good hole shot, then a 17P will give you excellent performance and time to plane. You just have to keep an eye on RPM as it's easy to overspeed.
Have you done WOT test with current prop yet?

[tech62571]

im not sure how to to do that

[mmwjr]

Originally Posted by tech62571

im not sure how to to do that

Find a nice open place on the water, get it up on plane then push the throttle all the way open. Record max RPM and Speed, this will be you WOT. For a more accurate reading turn the boat around and do it again in the opposite direction and then take the average of the two reading. This will account for current and wind influences.

[tech62571]

will do.. thank you

[tech62571]

finally got to do a WOT test.

at full throttle I'm at

5000 RPM and 40 MPH

[tech62571]

also do you think a stainless is better then Aluminum?

[jrsick]

That RPM and MPH works out to approx. 42 MPH with an 18 pitch prop, so that probably what you have since you see the number 18 stamped on your prop. I also see the 21, but don't think you have a 21 pitch prop because that would give you about 50 MPH. This is assuming your drive is a 1.98.
So your current prop size is probably going to be good for water sports and hole shots. If you're not really interested in water sports and just like cruising around, you should try and 21 pitch prop. It will bring your WOT closer to specs and give you higher top end.
I personally like aluminum because the blades flex, and, there is less shock transmitted to the outdrive if you hit something hard with your prop.

[tech62571]

not sure if it matters for the test but the prop is pretty nicked up.
is there a way to measure it to find the pitch?

[Phillbo]

Take it to a prop shop and they can refinish it for cheap. 5000 RPM sounds a bit high to me.. But not by too much. I'd think 4400-4800 would be the desired range.

[mmwjr]

I agree with the guys.

WOT should be 4400-4800. Aluminum prop flexes under load and will break if you hit something to reduce the forces being transmitted into the drives gears. A SS prop is heavy so it will load the engine more but with the proper pitch will give better low end performance.

[tech62571]

thanks everyone
hopefully they can tell me what it is as well. like to have a spare

[shrew]

Mercruiser engines are rated for a max RPM of 4400-4800. You are underpropped. If you have a 3 blade prop, you could go to a 4 blade, or stay with a 3 blade and go up 1" inch in pitch. Either should drop you down to 4800. You might do both, or stay with a 3 blade and go up 2" in pitch and drop to around 4600-4700.

You don't want to outside of the 4400 -4800 range.