Question regarding Pitch and 3 versus 4 blades

Greenchileman

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I'm a fairly new boat owner & need some help. We bought our 1st ever boat in August 2019 & it's a '04 model 2275RFS which is powered by a '13 model Suzuki 90HP. It's based on Lake Hartwell GA & came equipped w/a 3 blade 13.25X19 aluminum Prop (I have to say this prop is a bit ragged around the edges). The WOT RPM (w/a lightly loaded boat) is 5000 w/a top speed of 23. The Suzuki owners manual says this motor (DF90A) should be in the 5500 to 6300 range. We don't pull tubes or anything else for that matter & usually just tool around the lake with 4 - 6 adults onboard & take in Sunsets.

Bottom line is that while I'm not necessarily a speed demon we would like the motor to run in the proper range of WOT RPM. A local mechanic recently checked the TACH (it passed) & suggested we try a 17 pitch or maybe drop to a 15 but before ordering a new prop, or 2, I wanted to see what other owner-operators might think. Also, before I forget, I've read where 4 blade props help with low speed handling so I'm wondering if going with a 4 blade makes any sense.

Any and all help is appreciated, thank you!
 

DejaWiz

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I would recommend dropping down to a 15-17 pitch stainless 3 blade or 15 pitch 4 blade.

 

Greenchileman

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Thank you for sharing the link & recommendations. I’ll check out the Rubex site. Thanks again & have a great evening.
 

DejaWiz

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Thank you for sharing the link & recommendations. I’ll check out the Rubex site. Thanks again & have a great evening.

Glad to help. Good luck and I hope you are able to attain your performance goals!
 

the-little-B

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Im running a 20’ two 25” tube bennington with a 90hp yamaha. I have to disagree with the suggestions given to you. 15 and up is too much prop. My sweet spot is a 13.8x13 3 blade when im alone running light. 5900 rpm at 27-28 mph. And I’ll bet $100 that you wont have the power to turn a 15 pitch 4 blade. I tried a 13 pitch 4 blade and was low 5k rpms. I had to drop to an 11 pitch 4 blade to get in to the rpm range.
 

DejaWiz

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Im running a 20’ two 25” tube bennington with a 90hp yamaha. I have to disagree with the suggestions given to you. 15 and up is too much prop. My sweet spot is a 13.8x13 3 blade when im alone running light. 5900 rpm at 27-28 mph. And I’ll bet $100 that you wont have the power to turn a 15 pitch 4 blade. I tried a 13 pitch 4 blade and was low 5k rpms. I had to drop to an 11 pitch 4 blade to get in to the rpm range.

He's turning a 19 pitch now, and it would really depend on the physical characteristics of the prop, such as blade area, cupping, etc.
 
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Greenchileman

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Thanks for the additional input - I’m researching away & will report back when able. Thanks again for your time & enjoy what’s left of your night.
 

the-little-B

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The 19 is turning but it isnt turning well is it? I just went through the prop game with my 90hp over the last 2 summers so I have a little experience here.
 

DejaWiz

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The 19 is turning but it isnt turning well is it? I just went through the prop game with my 90hp over the last 2 summers so I have a little experience here.

No, it isn't. 5000 RPM for WOT is pretty dismal.
 

Vikingstaff

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As you are hearing above, some differing thoughts on it. Based on RPM’s and normal pitch vs. RPM changes, I would have initially advised a 15p because on paper it looks like it would get you to about 6000-6100 RPM. However, with “the-little-B” sharing their thoughts and experience after trying to dial in their 90 HP Yammy, that is powerful advise to follow. I would get on the same page on alum vs. SS in considering that advice.

IMHO, I would however suggest going/staying with aluminum. I think anytime someone’s motor is less than 115HP (And I debate it even with a 115HP), they should go aluminum. I would not even do a SS prop on a pontoon/tritoon unless I had a 150HP and up.

First, alum. is cheaper. Second, although the SS doesn’t flex with high HP motors and thus provides better performance, that is lost on smaller HP motors that wont flex the alum. prop. And although the alum WILL flex and cost you performance with high HP motors, It doesn’t with lower HP motors.

...so why spend more $$$ for a prop that will work your motor more to spin and yet wont give you appreciable performance increases? Also, if you hit stuff with an aluminum prop, you are more likely to just damage the prop. Hit stuff with a SS that doesn’t give way and is more solid, it transfers that strike Force to the lower unit of your motor. Potentially causing costly motor repair damage. Thus, with a 90 HP, I wouldn’t go SS. I would strongly suggest going aluminum with that motor. However, this decision also plays into prop pitch.

My above opinion on going alum. also begs a couple questions with the above posts: (1) what do you have now, alum or SS? That helps gauge what to drop down to. (2) Is little-B’s advise based on alum or SS? How’s that compare to what you have now? It is easy to be talking two different things here without those key details.

No matter what, best of luck to you. You’ll get it figured out. You certainly came to a great spot for real world advise like the advise you are getting above.
 

DejaWiz

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As you are hearing above, some differing thoughts on it. Based on RPM’s and normal pitch vs. RPM changes, I would have initially advised a 15p because on paper it looks like it would get you to about 6000-6100 RPM. However, with “the-little-B” sharing their thoughts and experience after trying to dial in their 90 HP Yammy, that is powerful advise to follow. I would get on the same page on alum vs. SS in considering that advice.

IMHO, I would however suggest going/staying with aluminum. I think anytime someone’s motor is less than 115HP (And I debate it even with a 115HP), they should go aluminum. I would not even do a SS prop on a pontoon/tritoon unless I had a 150HP and up.

First, alum. is cheaper. Second, although the SS doesn’t flex with high HP motors and thus provides better performance, that is lost on smaller HP motors that wont flex the alum. prop. And although the alum WILL flex and cost you performance with high HP motors, It doesn’t with lower HP motors.

...so why spend more $$$ for a prop that will work your motor more to spin and yet wont give you appreciable performance increases? Also, if you hit stuff with an aluminum prop, you are more likely to just damage the prop. Hit stuff with a SS that doesn’t give way and is more solid, it transfers that strike Force to the lower unit of your motor. Potentially causing costly motor repair damage. Thus, with a 90 HP, I wouldn’t go SS. I would strongly suggest going aluminum with that motor. However, this decision also plays into prop pitch.

My above opinion on going alum. also begs a couple questions with the above posts: (1) what do you have now, alum or SS? That helps gauge what to drop down to. (2) Is little-B’s advise based on alum or SS? How’s that compare to what you have now? It is easy to be talking two different things here without those key details.

No matter what, best of luck to you. You’ll get it figured out. You certainly came to a great spot for real world advise like the advise you are getting above.

That certainly is sage advice.
I would like to point out that Rubex Solas SS props are quite affordable...they can be had for under $300, which is a stout bargain.
And, dimensionally, very similar to their aluminum brethren.

That being said, your point about SS usually not being needed for lower-HP applications rings with merit, and there is no denying the value since these aluminum variants from Rubex can be aquired for less than $100.
 
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AuthorizedUser

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Im running a 20’ two 25” tube bennington with a 90hp yamaha. I have to disagree with the suggestions given to you. 15 and up is too much prop. My sweet spot is a 13.8x13 3 blade when im alone running light. 5900 rpm at 27-28 mph. And I’ll bet $100 that you wont have the power to turn a 15 pitch 4 blade. I tried a 13 pitch 4 blade and was low 5k rpms. I had to drop to an 11 pitch 4 blade to get in to the rpm range.
Finally! Someone who owns a boat that is very similar to the one I just ordered today! I am buying sight-unseen... never stood in my model, nor ridden in my model (although I've scampered about similar boats in the showroom and I have been on pontoons before). My 20SLG 2-tube comes with a Yamaha 90HP VMAX SHO motor. It's just me and my wife (and little doggie). I have no idea what prop comes with the motor (I don't think Bennington ships with a prop; I think my dealer will install one?) nor do I know how fast she'll go with the two of us at WOT. 27-28 is amazing and I would love to get similar results as you. Tell me, please, what prop do I tell me dealer I want so I can max the highest speed? Is it the 13.8x13 aluminum 3-blade? THANK YOU!
 

Greenchileman

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Thanks for the feedback. New development. A neighbor has offered up a practically new 3 blade aluminum Solas “Amita” (13 7/8 X 17) that will work on our motor so we’re going to run it & see what happens. I‘d love to have it be the one that does the trick however it does appear we’ll probably need to go with a lower #. That said, we’ll give this 17 a try and see what happens.

I’ll report back with #’s when able. Til then, thanks again everyone & enjoy what’s left of your Saturday!
 

Potomacbassin’

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4 blade makes sense if you want hole shot for popping water skiers, pulling tubers or moving a lot of weight, but as Dejawiz stated there are many variables to prop design (cup, rake, etc) beyond simple blade count, diameter and pitch. In some cases a 4-blade can actually have better overall performance than 3-blade, so there aren’t any absolutes out there (my buddies Ranger 522D ran a couple mph faster with a Rev4 than the dealer provided 3 blade). That being said, based on what I’ve read in performance bulletins, prop selectors and other forums you’re likely in that 13-15” pitch range for a 3-blade all around performance prop. Ken at Propgods can help/sell you the correct prop and Bennington will also look at their database and give you a good starting point.

As far as the SS vs aluminum debate, there is merit to what everyone has said - I happen to run (trolling speed) in shallow water quite a bit so my SS prop is going to barely get scuffed while an aluminum would look like a Nylabone after a dog chewed on it. The durability and performance for me offsets the big premium.

I would start with the 15 and go from there. Keep in mind that you have a Zuke which I believe has a higher gear ratio than Yam and Merc so you may be able to handle that pitch, but only way to know is test it. Other factors such as fouling on the toons, motor mounting height, poor motor maintenance etc can also factor in on your test data and may give a false reading.

Let us know the results! Good luck!
 

Greenchileman

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Hello from Georgia and thank you for the feedback. I've got 2 props that folks in our area have "donated" to us for testing. A 13.5 X 15 & a 13 8.75 X 17 (both are made by Solas & 3 blade). The models are as follows...15 pitch is a Rubex 3 & the 17 is called an Amita 3.

We are going to take the 13.25 X 19 off late next week then run both & record what happens at WOT.

As it currently stands, WOT with the 13.25 X 19 (only me onboard, smooth water, no wind and 20 gallons of fuel) is 5000RPM and 22-23MPH. This boat (2250RFS)is 22' long, has 25" toons and lifting strakes. I'll report back with results ASAP. Til then, thanks again for everyone's feedback & enjoy your Friday/weekend!
 

Potomacbassin’

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If I could recommend one other thing, don’t just record RPM at WOT but also speed at different RPMs and fuel efficiency (if you have the ability). You may find that many props give you close to the same top end (and target RPM) but the low and mid-range are dramatically different than the others. For example I had a Reliance 14x17 that topped out the same as a SWSII 15x19 (46 mph) but the Reliance was an absolute dog up to 4000 RPM due to insufficient diameter. The main impact was that my cruise fuel efficiency would suffer and cost me more $$ in the long run. At 25 mph it was 3.5mpg versus 2.5mpg.

Recording additional data points will give you a complete picture of the prop which in the end will help you make the best choice.

Just a suggestion!
 

Greenchileman

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Thanks for the additional info. We don’t have a fuel flow gauge but I have an idea for calculating the fuel burn at mid versus top end on both props. I’ll report back when able. Thanks again and have an excellent weekend!
 

Greenchileman

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Good late afternoon all. Sorry this report back took so long but we finally mounted the 3 blade 15 pitch Rubex 3 late last Thursday afternoon with very light Lake traffic and zero wind. I was onboard solo with my 25 gallon fuel tank at 3/4 full. WOT brought TACH to 5600 with a Top Speed of 26MPH. As for the 17 pitch prop, knowing that mounting it will almost certainly drop the WOT RPM back down to somewhere between 5600 and 5000 (that the old chewed up 19 produced) I'm thinking why even bother. I'm happy with the #'s the 15 has delivered. Factor into that the 15 was brand new in the box & all I paid for it was a bottle of decent 12 year old Scotch. That's it, just wanted to report back with the #'s. Thanks again to everyone for their feedback and have an excellent evening!
 

Potomacbassin’

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Thanks for the follow up, always great to see how these prop trials end up! You could also pick up a few RPM by raising the motor one hole, assuming you aren’t blowing out with some trim.

Given that you are at the bottom of the Zuke range with 1 person, once you carry a load of bodies and gear you’ll probably drop outside that range. Keep an open mind about dropping pitch if that happens to make that motor happy! Maybe stock up on some more scotch and try a few more props?:)
 

Greenchileman

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That’s a great idea & now that you’ve mentioned it, the mechanic who completed the last annual service talked about moving the motor up a notch too so maybe we‘ll bring that into play as well. I’ll report back when able. Thanks again & have an excellent day!
 
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