Anyone tried an 18” prop

[spikew919]

Anyone tried an 18” prop on the boats that come with a 17”? Looks to be room.  If you get the same pitch then wouldn’t it lower your rpm’s? 

[Jhucke]

32 minutes ago, spikew919 said:

Anyone tried an 18” prop on the boats that come with a 17”? Looks to be room.  If you get the same pitch then wouldn’t it lower your rpm’s? 

It is not safe to assume that slapping a prop on with an extra inch in diameter is going to give you the desired performance advantage.  Larger diameter is going to lower required RPM, sure, but to spin the prop, the engine must be capable of delivering the appropriate amount of torque.  If not, you'd have to step down to a lower pitch.  And from there, who knows what would happen to your top end/ performance everywhere else, probably nothing good.  Prop shapes require a lot of R&D to get right.  Having said that, why not just call ACME or whoever else to ask?

[23LSVOwner]

It also can put the prop close enough to the hull to cause cavitation burns to the hull bottom.

[spikew919]

1 hour ago, Jhucke said:

It is not safe to assume that slapping a prop on with an extra inch in diameter is going to give you the desired performance advantage.  Larger diameter is going to lower required RPM, sure, but to spin the prop, the engine must be capable of delivering the appropriate amount of torque.  If not, you'd have to step down to a lower pitch.  And from there, who knows what would happen to your top end/ performance everywhere else, probably nothing good.  Prop shapes require a lot of R&D to get right.  Having said that, why not just call ACME or whoever else to ask?

I’m well aware of how it all works. And did call and apparently it hasn’t been tried. Was more or less curious if anyone had tried it.  I would think the supercharged raptor motor should spin it since the Lt4 on the new m240 does. 

 

1 hour ago, 23LSVOwner said:

It also can put the prop close enough to the hull to cause cavitation burns to the hull bottom.

I have 1 and 1/2” of clearance now with the 17” so I would still have 1” of clearance. That shouldn’t be an issue should it? 

[TallRedRider]

It has been tried on the G23 fairly extensively.  I know it is not a precise comparison, but I dare say it is comparing red apples to green apples.  Both have 2:1 Transmission and 450hp or supercharged GM blocks.  A few guys messed around with various pitches as well.  I don't recall all the details, but it basically left me happy with what I had.   A surprising result to many was that the surf RPM's could be lowered with the bigger prop, but despite the decreased RPM's fuel consumption went up, i.e. it was lugging the motor.  Lowering RPM's is not the full story.  I will see if I can find the thread, it went on for quite a while.  uggh, 15 minutes of searching and I cannot find it.  

@spikew919, what would you hope to achieve?  I currently can get to surf speeds with what I consider to be infinite number of people in the boat and full ballast.  Wakeboard speed is another subject.  

Edited June 9, 2020 by TallRedRider

[spikew919]

9 minutes ago, TallRedRider said:

It has been tried on the G23 fairly extensively.  I know it is not a precise comparison, but I dare say it is comparing red apples to green apples.  Both have 2:1 Transmission and 450hp or supercharged GM blocks.  A few guys messed around with various pitches as well.  I don't recall all the details, but it basically left me happy with what I had.   A surprising result to many was that the surf RPM's could be lowered with the bigger prop, but despite the decreased RPM's fuel consumption went up, i.e. it was lugging the motor.  Lowering RPM's is not the full story.  I will see if I can find the thread, it went on for quite a while.  

@spikew919, what would you hope to achieve?  I currently can get to surf speeds with what I consider to be infinite number of people in the boat and full ballast.  Wakeboard speed is another subject.  

I can currently get to surf speed with any amount of people as well. Was just wanting to lower rpms a bit while cruising. Am currently running the 3077 and am thinking about the 3313. Both are 15.5 pitch. Cup is a little different. And actually my boat has 1.75 to 1 instead of the 2:1 I know this due to having to replace the vdrive last year under warranty but a long float down the river without another boat In site and pure hell to get on the trailer with my wife and daughters. 😂😂 

Edited June 9, 2020 by spikew919

[23LSVOwner]

1 hour ago, spikew919 said:

I have 1 and 1/2” of clearance now with the 17” so I would still have 1” of clearance. That shouldn’t be an issue should it? 

You could give it a shot.

[CJAY]

My big question is the prop shaft built to take the extra stress.  I'd compare the shaft of the MC boats running 18s to boats running 17s.  I remember the Gs having issues when they first came out due to the 17inch props

[spikew919]

3 minutes ago, CJAY said:

My big question is the prop shaft built to take the extra stress.  I'd compare the shaft of the MC boats running 18s to boats running 17s.  I remember the Gs having issues when they first came out due to the 17inch props

Aren’t the shafts stainless? Shouldn’t a stainless Aqualoy shaft 1and1/4 for boat use be the same strength?  

[CJAY]

7 minutes ago, spikew919 said:

Aren’t the shafts stainless? Shouldn’t a stainless Aqualoy shaft 1and1/4 for boat use be the same strength?  

No idea, not an expert on it, but I do know the early G's were snapping shafts with the 17s and had to change the diameter.

[TallRedRider]

G's have been snapping shafts all the way from inception to 2019.  It seems they finally got it figured out.  1 1/4 instead of 1 1/8  did not fix the problem.  They kept complaining it was their shaft manufacturer repeatedly, but multiple changes did not fix the problem, until 2019.  It seems shafts are no longer breaking.  And these were breaking before the 2:1 tranny and 17 inch props.  Some theorize it is the NSS that causes some unequal stress on the shaft through the rotation, others blamed the keyway.  

Here's 44 pages worth if you have the time:  https://www.planetnautique.com/vb5/forum/nautique-topics/general-nautique-discussion/27879-g23-prop-fell-off

 

[spikew919]

It’s so shiny. Lol. More to come 😁https://www.amazon.com/photos/shared/Lj2MBUq1ScyzdjfeaDhAdw.lnP_6ATphhCSB-TuD0Zkg7

[TenTwentyOne]

On 6/9/2020 at 4:42 PM, CJAY said:

My big question is the prop shaft built to take the extra stress.  I'd compare the shaft of the MC boats running 18s to boats running 17s.  I remember the Gs having issues when they first came out due to the 17inch props

Same 1 1/8” shaft on MCs, no matter if boat has 15.25”, 16”, 17.25”, or 18” diameter prop.

[TallRedRider]

34 minutes ago, TenTwentyOne said:

Same 1 1/8” shaft on MCs, no matter if boat has 15.25”, 16”, 17.25”, or 18” diameter prop.

This is one observation that has led some to believe that the key slot has something to do with props breaking on nautiques.  Splined shaft MC boats do not seem to have any busted shafts, compared to literally hundreds of G23's.  

[Texan32]

Hard edges will kill a shaft in a heart beat.  This has been proven over and over in the offroad community for decades.  There are plenty of mfgrs that use smaller diameter shafts that out perform cheaper larger diameter shafts for the simple fact that 1) they use higher quality allow as a base material, 2) they cold roll or hob the splines, and 3) they do not have any hard transitions (e.g. the shafts taper down before enlarging to make the splined portion).  Machining any edge on a shaft creates stress points on the shaft and is usually where they break.

is just an example of how stress works though a shaft. 

[Texan32]

14 hours ago, TallRedRider said:

This is one observation that has led some to believe that the key slot has something to do with props breaking on nautiques.  Splined shaft MC boats do not seem to have any busted shafts, compared to literally hundreds of G23's.  

Has anyone ever mic'ed our our prop shaft holes on both sides?  Is there a taper?  If so, that helps share the load onto the shaft.  If not, that means the key is the only thing that actually translates the power to the prop. 

BUT....lets not forget that they keys used on our props are designed to be a weak link.  Again, like the offroading world, you can outfit a driveshaft to have a 14010 u-joint that is strong enough to lift a 747 off the ground.  But, using a smaller 1330 or 1350 u joint means (maybe) the u joint fails before an axle shaft snaps.  And on the trail, replacing a u-joint is a 15 minute fix.  Snapping a shaft ends your day.  Its an engineered weak link. 

Now, if the G is breaking shafts before sheering a key (meant to be a weak link point).....that just means the shaft is a garbage design, uses weak alloy composition or gets an improper heat treatment.

[TenTwentyOne]

21 hours ago, Texan32 said:

Has anyone ever mic'ed our our prop shaft holes on both sides?  Is there a taper?  If so, that helps share the load onto the shaft.  If not, that means the key is the only thing that actually translates the power to the prop. 

BUT....lets not forget that they keys used on our props are designed to be a weak link.  Again, like the offroading world, you can outfit a driveshaft to have a 14010 u-joint that is strong enough to lift a 747 off the ground.  But, using a smaller 1330 or 1350 u joint means (maybe) the u joint fails before an axle shaft snaps.  And on the trail, replacing a u-joint is a 15 minute fix.  Snapping a shaft ends your day.  Its an engineered weak link. 

Now, if the G is breaking shafts before sheering a key (meant to be a weak link point).....that just means the shaft is a garbage design, uses weak alloy composition or gets an improper heat treatment.

They are tapered in a Bu, and most of the load is carried by the taper friction. A lot of shops will even use a lapping compound so that they seat as perfectly as possible.

Having a key as the weak point is definitely used in a lot of applications. This isn’t one of them. The keys are AQ-17, and they will chew out the inside of the prop hub way before they will shear that key. The weak point is the prop itself.

same on the splined shaft setup in a MC, the prop is the weak point.

 

@TallRedRider - Ya, that seems to be right where those shafts snapped. Cold rolled splines are definitely a stronger setup. That said, I believe there was definitely more to it, and I’d say it was likely the shaft alloy. Essentially, it seems the keyway made a weak point in an already weak shaft.

 

[spikew919]

Got a chance to try the 3313 prop today. And was pleasantly surprised, it out performed the 3077, 17” prop in every way. Rpms lowered by 400 give or take, had 9 people on boat and all ballast full and full of fuel and easily got up to surf speeds all the way to 13mph stretching the wave on out. Got up to speed faster than the 17” prop ever did. The motor isn’t working as hard so sound is down a good bit also. And didn’t bother checking but pretty sure fuel consumption went down also.   

[Rmichaelj]

Sounds like a winner as long as the shaft holds. What year/model boat do you have?

[asnowman]

On 6/14/2020 at 11:16 PM, Rmichaelj said:

Sounds like a winner as long as the shaft holds. What year/model boat do you have?

Pretty sure spike is still rocking the 2017 m235