Prop Pitch Recommendation

[jslaughter]

I run a 92 Nitro 190 DC with a 150 Evinrude on the back. When I first got the boat it came with a 24p prop. When I was low on gas and the only one in the boat it popped up and ran fine. But when I had a tournament load and 2 people, my coangler had to sit on the front to get it to plane.

I got a screaming deal on a 19p 4 blade so I took it. Been running it for a couple of years now but the RPM get up so fast. I hit 6k and am only doing about 41-43 mph. I know the RPM should be around 5500 so I need to switch to another prop.

 

Obviously its an older motor (15 spline) so I cant run over to my neighbor and borrow a prop to test. I was looking at a 4 blade 21p. But all the prop places dont allow returns or exchanges after use. So I am worried a 21 may still be a bit off after I test it and need to go to a 22p. 

 

Any suggestions?

[Hiteck22]

20 hours ago, jslaughter said:

I run a 92 Nitro 190 DC with a 150 Evinrude on the back. When I first got the boat it came with a 24p prop. When I was low on gas and the only one in the boat it popped up and ran fine. But when I had a tournament load and 2 people, my coangler had to sit on the front to get it to plane.

I got a screaming deal on a 19p 4 blade so I took it. Been running it for a couple of years now but the RPM get up so fast. I hit 6k and am only doing about 41-43 mph. I know the RPM should be around 5500 so I need to switch to another prop.

 

Obviously its an older motor (15 spline) so I cant run over to my neighbor and borrow a prop to test. I was looking at a 4 blade 21p. But all the prop places dont allow returns or exchanges after use. So I am worried a 21 may still be a bit off after I test it and need to go to a 22p. 

 

Any suggestions?

I have recently gone through Prop selection academy at the school of hard knocks and expensive props haha. And what I have learned is 1 inch of prop pitch change equate to roughly 150-200 RPM change. The 24P prop you had is really designed for high speed as compared to lower pitch props. Forgive me if you know this already but for the sake of being thorough, the higher the pitch, the further forward you boat travels forward at speed with each rotation of the prop. So reducing the pitch to a 19 for example you would travel less distance with each rotation, but the physics of that pitch mean your outboard can transfer power easier, meaning better acceleration and torque for getting on plane. The downside is that when you are at speed and on plane at wide open throttle (WOT) it will be turning faster than the 24P. Its like a 10 speed bike, you can't start on the lowest gear (equivalent to the 24p prop) because it is difficult to get started from a stop, but when you are going fast that's the gear you want to be in to travel the greatest distance with each rotation of the pedals so you don't have to pedal so fast to maintain speed. The opposite is true on the bike, if you start in the higher gear (equivalent to the 19P prop & easiest to pedal gear) you can get going from a stop easily, but when you are going fast you would be peddling like a tasmanian devil on meth. Assuming the prop diameter is the same, going from a 19P to a 21P should reduce your RPM's by roughly 300-400 RPM at WOT. You will loose some low end grunt and the time it takes to get on plane will worsen a bit but you wont be running your motor too hot at WOT. Chicks dig $$$ more than speed and you will have less $$$ if you have to re-power the old girl.

 

There are variables, engine mounting height, whether or not one of the props is cupped and another might not be, etc. but the 150-200 RPM per inch of pitch is the rough guideline. Another factor is the material. Stainless props spin faster than aluminum typically so just a swap in materials will have an effect on the RPMs at WOT as well.

 

Unfortunately you need to decide what is more important, the ability to get on plane and do so quickly, or maximum top end speed. A higher pitch prop will give you better top end speed at the expense of torque which will hinder your ability to plane or plane quickly. The inverse is true for a lower pitch prop.

 

So if the diameter is the same, and you should check that, going from the 19P to the 21P should get your RPMs closer to 5600-5700 if you were at 6000 previously. I like to play it safe and am a conservative guy who worries about blowing up the engine, the reason I just played prop whack-a-mole was having to re-power after blowing an engine. Don't worry, it didn't blow because of the prop and thus making this advice suspect haha. If it was me I would skip the 21P and go for the 22P. That theoretically would get you closer to 5400RPM than 5600 RPM at WOT and I would feel more comfortable with that. You should look in your user manual, they are pretty easy to find for free online, and confirm the recommended RPM at WOT.

 

For my boating needs, mostly fishing but no serious tourneys where drag racing to "the spot" is "critical", I value ability to get on plane more than top MPH so I tried to prop for that scenario. Being able to reliably plane out makes boating easier and safer in my opinion. So I think that a 22P would be the safest way to go. A 21P will accelerate a bit faster and help with planing a bit as compared to the 22P but will probably have your RPMs still a touch over the 5500 you are shooting for. That being said, you haven't blown it up at 6000 RPM yet so whats the diff between 5600 RPM and 5400 RPM????

 

Hope this helps!

 

 

 

 

 

[WRB]

Props come in a wide verity of designs and materials.

Aluminum and stainless steel are normal for fresh water bass boats.

3 and 4 blade props.

Pitch, rake and cup and blade design determines prop performance. You need to factor in slippage, prop turning in the water doesn't equal moving the boat 1 pitch forward.

Not being familiar with the 150 hp Evinrude outboard hp rating at prop shaft or powerhead makes it difficult recommend a specific prop. Merc has a online prop selector that maybe of some help.

A phone call to a local prop shop may help you. Phil's Prop shop in Redding CA isn't too far and they ship everywhere and knowledgable.

If you are over reving your 19P prop it's obvious wrong for your boat and engine.

Tom 

[jslaughter]

On 3/30/2020 at 2:48 PM, Hiteck22 said:

I have recently gone through Prop selection academy at the school of hard knocks and expensive props haha. And what I have learned is 1 inch of prop pitch change equate to roughly 150-200 RPM change. The 24P prop you had is really designed for high speed as compared to lower pitch props. Forgive me if you know this already but for the sake of being thorough, the higher the pitch, the further forward you boat travels forward at speed with each rotation of the prop. So reducing the pitch to a 19 for example you would travel less distance with each rotation, but the physics of that pitch mean your outboard can transfer power easier, meaning better acceleration and torque for getting on plane. The downside is that when you are at speed and on plane at wide open throttle (WOT) it will be turning faster than the 24P. Its like a 10 speed bike, you can't start on the lowest gear (equivalent to the 24p prop) because it is difficult to get started from a stop, but when you are going fast that's the gear you want to be in to travel the greatest distance with each rotation of the pedals so you don't have to pedal so fast to maintain speed. The opposite is true on the bike, if you start in the higher gear (equivalent to the 19P prop & easiest to pedal gear) you can get going from a stop easily, but when you are going fast you would be peddling like a tasmanian devil on meth. Assuming the prop diameter is the same, going from a 19P to a 21P should reduce your RPM's by roughly 300-400 RPM at WOT. You will loose some low end grunt and the time it takes to get on plane will worsen a bit but you wont be running your motor too hot at WOT. Chicks dig $$$ more than speed and you will have less $$$ if you have to re-power the old girl.

 

There are variables, engine mounting height, whether or not one of the props is cupped and another might not be, etc. but the 150-200 RPM per inch of pitch is the rough guideline. Another factor is the material. Stainless props spin faster than aluminum typically so just a swap in materials will have an effect on the RPMs at WOT as well.

 

Unfortunately you need to decide what is more important, the ability to get on plane and do so quickly, or maximum top end speed. A higher pitch prop will give you better top end speed at the expense of torque which will hinder your ability to plane or plane quickly. The inverse is true for a lower pitch prop.

 

So if the diameter is the same, and you should check that, going from the 19P to the 21P should get your RPMs closer to 5600-5700 if you were at 6000 previously. I like to play it safe and am a conservative guy who worries about blowing up the engine, the reason I just played prop whack-a-mole was having to re-power after blowing an engine. Don't worry, it didn't blow because of the prop and thus making this advice suspect haha. If it was me I would skip the 21P and go for the 22P. That theoretically would get you closer to 5400RPM than 5600 RPM at WOT and I would feel more comfortable with that. You should look in your user manual, they are pretty easy to find for free online, and confirm the recommended RPM at WOT.

 

For my boating needs, mostly fishing but no serious tourneys where drag racing to "the spot" is "critical", I value ability to get on plane more than top MPH so I tried to prop for that scenario. Being able to reliably plane out makes boating easier and safer in my opinion. So I think that a 22P would be the safest way to go. A 21P will accelerate a bit faster and help with planing a bit as compared to the 22P but will probably have your RPMs still a touch over the 5500 you are shooting for. That being said, you haven't blown it up at 6000 RPM yet so whats the diff between 5600 RPM and 5400 RPM????

 

Hope this helps!

 

 

 

 

 

 

All I can say is d**n! This is a lot of really good info and the reason I posted on here. Unfortunately it sounds like you learned in the hardest way possibly lol I did think a 22p was the way to go but was worried about the fully loaded planing issues too. Nothing is worse then being boat number 3 and cant get on plane. Been there, done that.

[WRB]

4 blade prop should resolve any hole shot issues but you loose a few mph on the top end at wot.

Contact a good prop shop.

Tom

[jslaughter]

9 minutes ago, WRB said:

4 blade prop should resolve any hole shot issues but you loose a few mph on the top end at wot.

Contact a good prop shop.

Tom

I actually tried giving your recommendation a call but Im assuming they are shut down just like every other place in Cali. I did take your advice and called a local shop that was still open and they referred me to a prop shop. Ill let you know what they say! 

 

Thanks!

[bogfrog]

Ive used this calculator before with good results. It may help. You know you need to be below 24 and above 19, so if this calculator recommends a prop within those sizes it should be fairly accurate.

https://www.vicprop.com/planing_size.php

[WRB]

1 hour ago, jslaughter said:

I actually tried giving your recommendation a call but Im assuming they are shut down just like every other place in Cali. I did take your advice and called a local shop that was still open and they referred me to a prop shop. Ill let you know what they say! 

 

Thanks!

Iboat is located in Utah and listed as a Evinrude prop dealer, not familiar with them.

Tom

[Siebert Outdoors]

This is who I used to have my Raker blue printed and tweaked.  He also sells props.  He may be able to tweak your 24 to help.

http://www.marksprops.com/

 

Typically you need to make a decision on top end or hole shot.