Correct prop

[edebusk]

I'm trying to change my prop and I want to make sure I get the right size. I want to Increase pitch but not much, cany anyone help? The pictures are what's on it.

 

[Skybolt]

Looks like your prop is this one:

https://www.boats.net/propellers/search?product_sku=6EBA-SOLAS-9511-148-17&ui=propeller&CAGPSPN=pla&gad_source=1&gclid=Cj0KCQjwlZixBhCoARIsAIC745BBTXT9RbHfP6pDbd7L4XepUFgf6rybaAVo2DfWCQstu1JMyJm0PM8aAqOeEALw_wcB

Or a 14.8D x 17"pitch RH. So the question is do you currently get MAX RPM's at wide open throttle? If not going larger in pitch is going to bog the engine further. That said 15"x19" is a common prop size.

 

[edebusk]

Looks like your prop is this one:

https://www.boats.net/propellers/search?product_sku=6EBA-SOLAS-9511-148-17&ui=propeller&CAGPSPN=pla&gad_source=1&gclid=Cj0KCQjwlZixBhCoARIsAIC745BBTXT9RbHfP6pDbd7L4XepUFgf6rybaAVo2DfWCQstu1JMyJm0PM8aAqOeEALw_wcB

Or a 14.8D x 17"pitch RH. So the question is do you currently get MAX RPM's at wide open throttle? If not going larger in pitch is going to bog the engine further. That said 15"x19" is a common prop size.

I honestly can't remember off the top of my head what my rpms are at WOT with my current prop i think MAYBE!! 3500 steady about 32-33mph across calm waters but i really don't know precisely because it didn't sound like the rpms were matching the sounds. I was reading that going up one size wouldn't lower my rpms to much maybe couple hundred. Just wanted to get some more insight due to lack of boating experience.

 

[Skybolt]

To run the engine correctly and get the most amount of life from it, you shouldn't go above it's red line RPM value. Red line is referred to the values that are red on the tachometer or it's max RPM value. I believe an 87 is rated for 4200-4600 RPM.

To tune the prop to the correct value you judge it by the RPM range obtained at WOT. Speed is irrelevant but other things do contribute to obtaining max RPM, like trim. Both out drive and boat trim. If you have trim tabs installed then they are part of the equation as well. But on a boat your size the outdrive trim is used to achieve proper boat inclination and the tabs to level lateral balance.

To run the boat properly and achieve max RPM, start out getting the boat on plane with the drive down, then once leveled off increase the trim and the rpm's rise. In the right calm water conditions, you can raise the trim until slight cavitation is heard then dropping down a bit until it grabs and the prop is utilized 100%. At that point you should be at max RPM.

The above is one way of telling what max rpm is. After that is observed, then you can determine what pitch prop you can move too. The diameter is also a factor, but the outdrive determines that for the most part. Roughly every 2" in pitch is 100-200 in RPM. It's not an exact science and the results will change with the amount of weight in the boat. So try this with the boat loaded up with fuel, gear and at least two people.

 

[edebusk]

To run the engine correctly and get the most amount of life from it, you shouldn't go above it's red line RPM value. Red line is referred to the values that are red on the tachometer or it's max RPM value. I believe an 87 is rated for 4200-4600 RPM.

To tune the prop to the correct value you judge it by the RPM range obtained at WOT. Speed is irrelevant but other things do contribute to obtaining max RPM, like trim. Both out drive and boat trim. If you have trim tabs installed then they are part of the equation as well. But on a boat your size the outdrive trim is used to achieve proper boat inclination and the tabs to level lateral balance.

To run the boat properly and achieve max RPM, start out getting the boat on plane with the drive down, then once leveled off increase the trim and the rpm's rise. In the right calm water conditions, you can raise the trim until slight cavitation is heard then dropping down a bit until it grabs and the prop is utilized 100%. At that point you should be at max RPM.

The above is one way of telling what max rpm is. After that is observed, then you can determine what pitch prop you can move too. The diameter is also a factor, but the outdrive determines that for the most part. Roughly every 2" in pitch is 100-200 in RPM. It's not an exact science and the results will change with the amount of weight in the boat. So try this with the boat loaded up with fuel, gear and at least two people.

Thank for an educated response truly. I will run it first with the current prop and determine these number more accurately and go from there. I wasnt to concerned about going much faster if at all but I ready that you have a little more control with a higher pitch(correct me if I'm wrong). I had only planned on going up to a 19 pitch due to not fully understanding, but like I said, I'm still new to boating so I plan on asking and learning as much as I can.

 

[Skybolt]

Thank for an educated response truly. I will run it first with the current prop and determine these number more accurately and go from there. I wasnt to concerned about going much faster if at all but I ready that you have a little more control with a higher pitch(correct me if I'm wrong). I had only planned on going up to a 19 pitch due to not fully understanding, but like I said, I'm still new to boating so I plan on asking and learning as much as I can.

Better control would be a lower pitch prop to a point. Higher pitch puts more load on the engine and makes it less responsive to RPM changes.

 

[Scott215]

I use a 17 pitch prop. Holeshot is great and still have a great top end

 

[Stingrayaxe]

In addition to Skybolt’s very excellent explanation of determining the baseline for the current prop, I would also use a GPS app to to gather top end speed. Top speed might not be your end goal but having another data point to compare can be helpful when making a prop change.

 

[edebusk]

I use a 17 pitch prop. Holeshot is great and still have a great top end

Would there be much difference between a 19 pitch 3 blade and a 17 pitch 4 blade?

 

[Skybolt]

Would there be much difference between a 19 pitch 3 blade and a 17 pitch 4 blade?

Four bladed props are slower but punchier out of the hole.

 

[Stingrayaxe]

Also allows you to stay on plane at a lower speed. Reduces low speed wander a little bit. I prefer 4 blades as I don’t care about top speed as much as the other benefits over 3 blades.

 

[edebusk]

Also allows you to stay on plane at a lower speed. Reduces low speed wander a little bit. I prefer 4 blades as I don’t care about top speed as much as the other benefits over 3 blades.

And im thinking the same I don't care as much for speed. But I figured going to 4 blades with the same 17in pitch would be alright and wouldn't bog the motor down any

 

[Stingrayaxe]

Just follow Skybolts direction to get your baseline. Assuming your current prop puts your WOT at the high end of your motors recommended RPM range you can then make an educated guess on what prop to try. Generally lower pitch by 2 degrees when moving to a four blade. This should keep your RPMs in range. If not you might need to try another prop. You will lose a few MPH on the high end but you should see improvements in hole shot and low speed handling. Report back on your findings.

 

[edebusk]

I will get these figures understood and recorded and report back asap.

Thank you for the responses.

 

[Skybolt]

I will get these figures understood and recorded and report back asap.

Thank you for the responses.

What @Stingrayaxe is saying is if you move to a 4 blade the pitch of the 4 blade should be 2" less then the 3 blade and that should make things equal and still get WOT RPM. So if your current prop gets you max RPM at WOT then a 4 lade prop should be the same diameter and 2" less pitch, or even 1" and you might gain a little bit of performance back.

 

[techmitch]

Just follow Skybolts direction to get your baseline. Assuming your current prop puts your WOT at the high end of your motors recommended RPM range you can then make an educated guess on what prop to try. Generally lower pitch by 2 degrees when moving to a four blade. This should keep your RPMs in range. If not you might need to try another prop. You will lose a few MPH on the high end but you should see improvements in hole shot and low speed handling. Report back on your findings.

I will get these figures understood and recorded and report back asap.

Thank you for the responses.

This is a very important step so you can make an engine performance evaluation before moving forward.

 

[techmitch]

What @Stingrayaxe is saying is if you move to a 4 blade the pitch of the 4 blade should be 2" less then the 3 blade and that should make things equal and still get WOT RPM. So if your current prop gets you max RPM at WOT then a 4 lade prop should be the same diameter and 2" less pitch, or even 1" and you might gain a little bit of performance back.

You are faster.