Propeller Questions

[alan17]

I have a 2006 alpha one outdrive GR 1:62. 5.0 Merc, 220hp, WOT 4400 @ 46mph, I currently have a 4 blade SS 48-825900 19P . It has a bushing which slides over the shaft to hold the prop in place. A friend gave me a 3 blade SS AB Quicksilver 48-13704 A41 23P. It fits the existing shaft perfectly, however it is about 1/4" short at the end of the shaft. (The spline extends past the inside of the prop hub). 1. will this prop work on this outdrive? 2. Is there an adapter that I can purchase to overcome the long spline issue? 3. will the wot rpm be too much with this prop?

[Jango]

Can't help you with the bushing, but, the prop change should Decrease RPM,s , not Increase. While the 4 blades to 3 will increase RPM,s slightly, the 4in. Pitch change will more than offset the increase. My guess would be a 200 - 400 net decrease.
Also you will probably loose a significant amount of Hole Shot with the 23P

[pistnbroke]

A four blade prop is usually 4 pitchces less than the equivalent 3 blade so the 19/4 and 23/3 will be equivalent, usually changing the pitch by 2 inches changes the revs by 400 rpm

[Jango]

If your Engine is turning 4400 rpm with a 19 pitch, assuming the same HP, it will be turning 3650 rpm with a 23 pitch or 750 less (with the same no of blades) . In reallity, HP will be less at lower RPM,s, further reducing final RPM,s. I don't believe going from 4 to 3 blades, by itself would result in a 800 RPM increase. My 90 HP Evinrude saw less than a 400 RPM decrease going from a 3 blade to a very aggressive (Renegade) 4 blade.

Also, my Evinrude has a bronze bushing (13 spline) in front of the prop. You might check if one is available for your application which, I am sure is larger than my outboard shaft.

Again, I believe you will not be happy going to the 23 Pitch. Increasing the pitch does NOT necessarily increase speed as long as your motor is developing max HP at your current rpm. HP INCREASES SPEED.

[pistnbroke]

jango read the last two lines of my post ....the 19 p and 23 pitch are the same loading for the motor as an equivalent 4 blade is 4inches pitch less. The four blade has a bigger blade area hence the 4 blade has a higher load than a 3 blade and less slip .
The real question is what does he want to do with the rpm ..take it up or down ...a change of 2 in changes rpm by 400.

IF you want to go up by 400 rpm then fit a 17 pitch 4 blade or 21 pitch 3 blade
IF you want to go down 400 rpm then a 21pitch 4 blade or 25 pitch 3 blade

You can get the spacer washer with 15 splines from any mercury dealer ..I have two in stock

[alan17]

thanks for the info. one of the reasons i am asking is the new prop needs some work.. probably 150.00, didn't know if i needed to spend that for something that wouldn't work with my setup. Mostly the boat will be used for pulling kids up on wakeboards and skiis. when it is my turn I just like to cruise, faster the better...
thanks again
Alan

[Jango]

Not knowing how much your boat weighs with Driver only and half tank of fuel, one would have to estimate weight based on current performance. Using 3000#, a 23P, 3 Blade could get you to near 50 MPH, but with increased slippage. The 23P. will give you alot less Hole Shot even without skiers.
The 19P. 4 Blade is the better prop for your application - especially since you will be pulling skiers etc. As long as you are not overreving, your pitch is correct.