1400 RPM loss from 13 to 15 pitch!!!

[Miked3]

Boat- 2014 Lund Fury 1625 XL
Motor- 2014 Mercury 60hp 4 stroke elpt
Props- SPITFIRE PONTOON (13.8 X 13") MERCURY RH PROPELLER, 48-8M8026570 - 4 blade - 25mph @5500rpm
Hustler 3 blade 14 x 13- 25mph @6200rpm
Hustler 3 blade 13.75 x 15- 29mph@4800rpm

All these numbers were recorded using Vessel View. I used Vessel View with the 4 blade to calibrate my odometer and it then matched up for all of the testing.

I was expecting 5800rpm with the 15 pitch not a 1400rpm loss. What gives?

 

[Bondo]

Ayuh,...... Welcome Aboard,..... You hit the horsepower max, with the smaller prop, 'n it won't pull the bigger prop is my guess,......

 

[Miked3]

Ayuh,...... Welcome Aboard,..... You hit the horsepower max, with the smaller prop, 'n it won't pull the bigger prop is my guess,......

That much RPM loss seems excessive when average is supposed to be 200-250. Im getting 4 more mph with the 15 over the 13 and time to plane was fine. Im concerned about not cruising in the recommended 5500-6000 rpm range. Will 4800 rpm max be bad for the motor?

 

[Bondo]

Ayuh,.... Ya ran outa horsepower, you need the smaller prop,.....

Luggin' the motor like that, burns holes in pistons,.....

 

[Scott Danforth]

running that close, if you just cupped your 13P, you would have dropped from 6200 to 5800

as bondo stated, you ran out of HP at a point much sooner than the 15p prop curve

 

[QBhoy]

Boat- 2014 Lund Fury 1625 XL
Motor- 2014 Mercury 60hp 4 stroke elpt
Props- SPITFIRE PONTOON (13.8 X 13") MERCURY RH PROPELLER, 48-8M8026570 - 4 blade - 25mph @5500rpm
Hustler 3 blade 14 x 13- 25mph @6200rpm
Hustler 3 blade 13.75 x 15- 29mph@4800rpm

All these numbers were recorded using Vessel View. I used Vessel View with the 4 blade to calibrate my odometer and it then matched up for all of the testing.

I was expecting 5800rpm with the 15 pitch not a 1400rpm loss. What gives?

Hi there. Don’t take this the wrong way…but are we saying that these numbers were all taken from the vessel view (it’s rpm and gps speed)….or are we saying that these numbers were taken using analogue gauges that seemed to match the VesselView previously? Just trying to be sure around things, to try and think about what’s going on. Just when you said about calibrating an odometer there.

 

[QBhoy]

I’d also say that it may well be explained by the engine not being into its rpm range with the 15”. All the power is in the stated rpm range, which I’d guess starts at at least 5000ish rpm. More rpms comes more power. More rpms comes more lift from the prop too
So many variables and dynamics to think about with props. Perhaps more especially when talking about a boat like a pontoon perhaps.
In addition, if you’re using the vessel view function that states max speed and rpm achieved (when you press on the speed box)…I happen to know that it can give you a snap shot moment in time for rpm. Best to look at the rpm in real time to see what it’s doing at your max speed. If I do three consecutive max speed runs on mine (with a prop that won’t hit limiter)…I know for a fact the recorded data will say the same speed…but the rpm captured can vary a fair bit each time. Not hugely, but can be 100-200 rpm sometimes. But if you look at the real time data..it’s fairly steady

 

[Miked3]

Hi there. Don’t take this the wrong way…but are we saying that these numbers were all taken from the vessel view (it’s rpm and gps speed)….or are we saying that these numbers were taken using analogue gauges that seemed to match the VesselView previously? Just trying to be sure around things, to try and think about what’s going on. Just when you said about calibrating an odometer there.

All numbers are live from vessel view. I said odometer but meant I calibrated the RPM analog gauge to match vessel view using the 13 pitch 4 blade prop and the analog gauge has matched the vessel view live rpm ever since.

 

[Miked3]

I’d also say that it may well be explained by the engine not being into its rpm range with the 15”. All the power is in the stated rpm range, which I’d guess starts at at least 5000ish rpm. More rpms comes more power. More rpms comes more lift from the prop too
So many variables and dynamics to think about with props. Perhaps more especially when talking about a boat like a pontoon perhaps.
In addition, if you’re using the vessel view function that states max speed and rpm achieved (when you press on the speed box)…I happen to know that it can give you a snap shot moment in time for rpm. Best to look at the rpm in real time to see what it’s doing at your max speed. If I do three consecutive max speed runs on mine (with a prop that won’t hit limiter)…I know for a fact the recorded data will say the same speed…but the rpm captured can vary a fair bit each time. Not hugely, but can be 100-200 rpm sometimes. But if you look at the real time data..it’s fairly steady

Not looking at the snapshot but the live values for RPM and Speed as I make a run.

More rpm/power should equal more speed but it doesn't if you look at my numbers. Im getting more speed from the lower rom but higher pitch prop. No issues getting on plane. The boat is at full weight too so it is how it will normally be running.

So are we all thinking a 14 pitch is going to split the difference and give me 700rpm back?

The calculated slip on the 15 pitch is 1.

 

[dingbat]

More rpm/power should equal more speed but it doesn't if you look at my numbers.

Not necessarily. It’s called a torque “curve” for a reason. Once you pass peak HP (rpm) it’s drops off rapidly.

So are we all thinking a 14 pitch is going to split the difference and give me 700rpm back?

Doubt it.
You had a dramatic change because you changed prop designs. If you stay with the same prop design, your back in the 200 rpm per inch range.

The calculated slip on the 15 pitch is 1.

At what rpm?
Recommend running your slip calculation at the rpm you typically run. You might be surprised at the number

 

[jimmbo]

An odometer on a Boat. Must be a new gauge...

 

[jimmbo]

Are those Dia and Pitch numbers on the Prop, or just from the Box?
There is possibility that the Prop is mislabeled, as well

 

[QBhoy]

Not looking at the snapshot but the live values for RPM and Speed as I make a run.

More rpm/power should equal more speed but it doesn't if you look at my numbers. Im getting more speed from the lower rom but higher pitch prop. No issues getting on plane. The boat is at full weight too so it is how it will normally be running.

So are we all thinking a 14 pitch is going to split the difference and give me 700rpm back?

The calculated slip on the 15 pitch is 1.

The slip numbers give away that one or more of the data collected isn’t accurate. If you don’t mind me suggesting so. Suggests that the actual rpms were in reality a good bit higher, to bring the slip into the realms of normality. You’ll no doubt know yourself, that 1% slip is almost impossible for 99.9% of boats. Rarely, if at all, achieved for most. Especially not possible for a boat like your own, I’d be sure. Put the data into the prop slip calculation again, but put in a assumption of 10-15% slip and leave the rpm input blank…see what it suggests. That would be telling.

 

[QBhoy]

All numbers are live from vessel view. I said odometer but meant I calibrated the RPM analog gauge to match vessel view using the 13 pitch 4 blade prop and the analog gauge has matched the vessel view live rpm ever since.

The analogue gauges never do, I’ve found. But be an unusual thing to be able to calibrate the gauge perhaps. Fair play.

 

[Bondo]

So are we all thinking a 14 pitch is going to split the difference and give me 700rpm back?

Ayuh,.... Or as Scott suggests, have some more cup beat into yer 13" prop,.....

 

[QBhoy]

I’m of the opinion that the slip number of 1% is very telling. Really need to do another run and be certain of the numbers. Especially since the 13” prop is showing an uncertain rpm figure too. Apologies for doubting the numbers, but they just don’t make sense at all. That engine has a rpm range of 5500-6000 as far as I know. Given that…you’re at best on the limiter at 6200…at worst, I honestly don’t think that the limiter would allow you to reach 6200 rpm. My mercury has a range of 5000-6000 and it will not be allowed to reach 6200. Limiter is about 6100-6150 at most.
That aside, if it was even to reach 6200…it’s certainly limiting…so the actual rpm it could reach, if not for that, with the 13”…is unknown really

 

[Miked3]

Not necessarily. It’s called a torque “curve” for a reason. Once you pass peak HP (rpm) it’s drops off rapidly.

Doubt it.
You had a dramatic change because you changed prop designs. If you stay with the same prop design, your back in the 200 rpm per inch range.


At what rpm?
Recommend running your slip calculation at the rpm you typically run. You might be surprised at the number

No the big change is from the SAME Hustler prop! Please look at all my posted numbers again.

Slip calculation is from the 4800rpm at 29mph with the 15 pitch prop using the Mercury slip calculator.

Does no one find it strange I gained 4mph but dropped to 4800RPM?

 

[QBhoy]

No the big change is from the SAME Hustler prop! Please look at all my posted numbers again.

Slip calculation is from the 4800rpm at 29mph with the 15 pitch prop using the Mercury slip calculator.

Does no one find it strange I gained 4mph but dropped to 4800RPM?

I think it’s definitely strange, but have a read at my earlier post. The numbers just aren’t correct or even possible. Haven’t checked the slip and details for myself…but your own suggestion of 1% slip…just isn’t at all a possibility. Definitely worth another run out to check the numbers again. Read what I said about the rpm limiter and playing with numbers on the calculator again. Best of luck.

 

[Miked3]

The slip numbers give away that one or more of the data collected isn’t accurate. If you don’t mind me suggesting so. Suggests that the actual rpms were in reality a good bit higher, to bring the slip into the realms of normality. You’ll no doubt know yourself, that 1% slip is almost impossible for 99.9% of boats. Rarely, if at all, achieved for most. Especially not possible for a boat like your own, I’d be sure. Put the data into the prop slip calculation again, but put in a assumption of 10-15% slip and leave the rpm input blank…see what it suggests. That would be telling.

All size numbers were verified on the prop as that was my first thought too!

My original numbers with boat having no extra test weight with the 13 pitch 4 blade was 5700rpm @ 30mph. Slip came out to zero I believe. Once I added weight that it will normally operate with that prop delivered 5500rpm @25mph.

I no longer have the 3 blade hustler 13 prop. I did the trade they have to get the 15.

The 13 pitch was 14" diameter. The 15 pitch is 13.75" diameter.

 

[QBhoy]

All size numbers were verified on the prop as that was my first thought too!

My original numbers with boat having no extra test weight with the 13 pitch 4 blade was 5700rpm @ 30mph. Slip came out to zero I believe. Once I added weight that it will normally operate with that prop delivered 5500rpm @25mph.

I no longer have the 3 blade hustler 13 prop. I did the trade they have to get the 15.

The 13 pitch was 14" diameter. The 15 pitch is 13.75" diameter.

Ok. So you definitely need to go out and have another run. Zero prop slip is an impossible result. Not having a go by any means. Just trying to help. But yeah, certainly need another few tests. It’s just not possible to get that slip figure.
Keen to help out if I can. Do you know what gear ratio you have on your engine ? Think the model changed around that year or just after perhaps. One was 2 to one or close and the other might have been 1.8 something to one maybe. There may have been a Bigfoot or CT model with a lower ratio again too.