Prop Question

[rekogniz1]

I have a 91 Evinrude 150 and was running a 14 1/4 x 19 pitch SS 3 blade. I was getting 47 mph at 5000 rpm. I purchased a 14 1/4 x 17 SS 4 Blade and now only get 5000 rpm and 43 mph if lucky. I am going for higher RPM around 5500 and better speed. What went wrong here as I went down to a 17 and no RPM difference, just less speed.

 

[emdsapmgr]

Re: Prop Question

Likely due to the differences between the props. The old ss prop is basically a thinner version of an aluminum prop. They did not have much cup on them. The 4 blade is probably a hi-rake prop with lots of cup, making it more like an 18. You may be able to improve your prop performance by raising the engine up one notch on the transom. Cupped props will still maintain bite with part of the prop tip actually piercing the surface of the water. Less lowr unit in the water=less drag. Keep an eye on your engine temps and water pressures when you start to raise the engine above normal running heights.

 

[rekogniz1]

Re: Prop Question

Since I still have the option of returning the 4 Blade to get a different one would there be another selection I should try prior to moving the engine up a notch? If it helps the 3 blade is a Turbo brand prop and the new 4 Blade is a Solas (sizes listed above). Kind of frustrating that I spent 350.00 and just lost MPH and no gain in RPM.

 

[steelespike]

Re: Prop Question

The uncertainty of going from ss to al has been discussed here many times.
Besides the design differences when going to a 4 blade al the extra drag from the additional blade tends to reduce your top end rpm.So you reduced your pitch and rpm (stayed same)However;there should have been a noticeable improvment in hole shot and the ability to stay on plane at less power,as well as better response at no wake speed around the dock.The 4 blade may allow much more height so it might gain some rpm back but not likely to make 47.
You could have the ss repitched down or a little cup removed.I've seen some excellent result removing some cup.You just need to be sure the shop knows what they are doing.Raising the stock 19 ss to a point just before venting becomes a problem might gain some rpm and speed.2" could result in a couple of mph under ideal conditions.

 

[dazk14]

Re: Prop Question

If you were looking for more speed and rpm why did you switch to a 4 blade?

Which model Solas did you buy?

What is the WOT RPM range for your engine?

Not surprised the Turbo is faster - they've been in the business for a long time.

 

[rekogniz1]

Re: Prop Question

I think there is some confusion based on some of the replies:

Neither of my props are AL.....They are both SS.

1. With the Turbo 3 Blade 14 1/4 x 19 pitch, I was getting 5000 RPM and 47 MPH
2. With the Solas 4 Blade (HR Titan 4) 14 1/4 x 17 pitch, I was getting 5000 RPM and 43-44 MPH.

I went to the 4 Blade based on recomendation from forum and prop store. They said to get Higher RPM to go down on the pitch.

My Manual states 5800 max RPM WOT.

I am trying to get close to the 5800 RPM wich from my understanding should get me better performance as well as a little bit better speed if proped correctly.

 

[rekogniz1]

Re: Prop Question

I moved the motor up two holes which was about an inch in actual lift and will give it a shot. Should I keep the 4 Blade 17 pitch or should I go back to the 19 pitch 3 Blade since I moved the motor up. To emdsapmgr's point above, another local guy asked if I can trim all the way up with not much difference in RPM and the answer was yes. He also suggested that I should be able to trim all the up untill the prop cavitates and rpm goes up and then bump the trim down a bit which means I needed to lift the motor up as I cannot do that with my current setup.