Does NGR prop like pitch or RPM?

Airboat propeller discussion.
User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Wed Aug 17, 2016 3:24 pm

I have less than 20 hours on my prop, but to me it seems it should put out more thrust for a 3 blade prop. I have it pitched at the 3 mark and I'm getting 35 mph at 3600 rpms. I run mostly deep water. I wonder if I should put a little more pitch into it or to look at going from a 2.7 to a 2.38 gear box. I'm curious to see what you all think is best.
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
Tony480
Site Supporter - I
Site Supporter - I
Posts: 5275
Joined: Sun Sep 10, 2006 5:52 pm
Location: lake county

Re: Does NGR prop like pitch or RPM?

Postby Tony480 » Wed Aug 17, 2016 4:52 pm

What's your setup..speed has as much to do with setup,hull,motor,box and prop..not just prop

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Wed Aug 17, 2016 5:19 pm

Sorry Tony, I thought my signature showed my set up. It is a 13.6 Lazer hull with a SBC 383 stroker that puts out 425 horse. I currently have a 2.7 Ballistic gear drive and an 80 inch NGR 3 blade Prop. Does that help?
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

CarMotorBarge
Site Supporter - I
Site Supporter - I
Posts: 707
Joined: Thu Jul 14, 2011 8:32 pm
Location: Lake Harney Woods

Re: Does NGR prop like pitch or RPM?

Postby CarMotorBarge » Wed Aug 17, 2016 6:42 pm

What are the engine RPMs at WOT? What are the max RPMs you want to run the engine at?
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.68 Rotator soft drive swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer
Member of Seminole Airboat Club

User avatar
goldhunter_2
Site Supporter - III
Site Supporter - III
Posts: 8919
Joined: Mon May 23, 2005 7:17 pm
Location: Port Saint Lucie Fl

Re: Does NGR prop like pitch or RPM?

Postby goldhunter_2 » Wed Aug 17, 2016 7:38 pm

Des Moines Boater wrote:I have less than 20 hours on my prop, but to me it seems it should put out more thrust for a 3 blade prop. I have it pitched at the 3 mark and I'm getting 35 mph at 3600 rpms. I run mostly deep water. I wonder if I should put a little more pitch into it or to look at going from a 2.7 to a 2.38 gear box. I'm curious to see what you all think is best.


In my past experiences with ng series is they only seem to have one small sweet spot that they really produce in not a wide range like others so you have to really dial it in to where that sweet spot is for your motor not go on the pitch.
.


Support our future , get a kid involved in the outdoors!!

:rebel:



.


User avatar
Tony480
Site Supporter - I
Site Supporter - I
Posts: 5275
Joined: Sun Sep 10, 2006 5:52 pm
Location: lake county

Re: Does NGR prop like pitch or RPM?

Postby Tony480 » Wed Aug 17, 2016 10:30 pm

Honestly your mph doesn't seem far off..especially if it has poly. Also those laser hulls sre pretty narrow and aren't going to free up as well with a carmotor weight and power

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Thu Aug 18, 2016 12:45 pm

7 foot wide hull and no polly. I'm used to aircraft engines where the faster you turn the prop the more thrust you get. With the 2.7 at 3600 rpm I'm only turning the prop a little over 1300 rpm. The prop is rated to 2800. I just wonder if there is an advantage to go to a 2.38 ratio and turn the prop faster with less pitch at the same engine rpm or not. I have no problem getting on plane as soon as the engine hit 4000, I'm up and gone, slowing it back to 3500 or 3600 rpm to cruise. I know everyone likes the 2.68 ratio but a 2.38 looks tempting to me. Wish I could try one.
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
nebraskaairboater
Site Supporter - I
Site Supporter - I
Posts: 809
Joined: Thu May 06, 2004 12:42 pm
Location: Fremont, Nebraska
Contact:

Re: Does NGR prop like pitch or RPM?

Postby nebraskaairboater » Thu Aug 18, 2016 12:57 pm

whats your max rpm at wide open?
Dan Porter, Jr.
Fremont, NE
16 x 8 1971 Flat Bottom Fiberglass Hull / 500 Cadillac/ 2.12:1 Rotator / 80" 3-Blade Sensenich S

User avatar
Tony480
Site Supporter - I
Site Supporter - I
Posts: 5275
Joined: Sun Sep 10, 2006 5:52 pm
Location: lake county

Re: Does NGR prop like pitch or RPM?

Postby Tony480 » Thu Aug 18, 2016 2:11 pm

I turn an 82" -3 blade ngr with a 2.68 and 580 horse...my cruise is about 2600 and at 3500 I'm running around 40-44 mph in deep water

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Thu Aug 18, 2016 3:22 pm

My max rpm is 5200. I'll add a little more pitch and see if that gives me the cruise Tony has. My engine is 450 HP or maybe a little less. It hasn't been dyno checked.
2600 cruise is what speed? The prop is only turning 970 rpms. At 3500 it still only turning 1305 rpms. You must have a lot of pitch in that prop for those numbers. Maybe the answer is to add more pitch. At least at the 2.68 ratio slow speed the prop is quiet.
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
Tony480
Site Supporter - I
Site Supporter - I
Posts: 5275
Joined: Sun Sep 10, 2006 5:52 pm
Location: lake county

Re: Does NGR prop like pitch or RPM?

Postby Tony480 » Thu Aug 18, 2016 4:53 pm

I got 17.5° measured at the tip and turn it 6100...my usual cruise is 30-32mph

User avatar
Waterthunder
Site Supporter - VIII
Site Supporter - VIII
Posts: 8160
Joined: Fri Jan 21, 2005 3:16 pm
Location: Melbourne
Contact:

Re: Does NGR prop like pitch or RPM?

Postby Waterthunder » Fri Aug 19, 2016 1:09 pm

The NGR likes tip speed the tip is the same principal as a Whitcomb Winglet however at lower tip speeds its a drag and is not as efficient. But when tip speeds go up and the air being cast off of the standard tip blade goes up the winglet performs better than a standard tip. If you lay the thrust dyno graphs over each other the R blade produces more thrust until about the last 1500RPM's so from idle till about 4,800 the R is better but from 4,800 rpms and up the NGR is better. This is with a base 2.68 ratio and a 82'' 4 blade prop. ONE THING THE NGR KILLS THE R BLADE AT IS SOUND IT IS SUBSTANTIALLY QUIETER THAN THE R.
THE PROOF IS IN THE PROP!

"If you copy someone you will only achieve what has already been done."

http://waterthunder.com/
321-508-5316

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Fri Aug 19, 2016 2:01 pm

Thanks Dave for the reply. I like how quiet the prop is. I was just thinking I might be able to get the same performance out of it if I changed to a 2.37 instead of the 2.7 and take some pitch out. I'm already at the 3 mark. I was thinking the 2.37 gearbox would spin the prop faster and improve overall performance. I know you like the 2.68 box but I'm still not sure it is the right box for me. What are your thoughts?

Tony, I'll try setting my prop the same number of degrees as yours and go from there.
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
Waterthunder
Site Supporter - VIII
Site Supporter - VIII
Posts: 8160
Joined: Fri Jan 21, 2005 3:16 pm
Location: Melbourne
Contact:

Re: Does NGR prop like pitch or RPM?

Postby Waterthunder » Fri Aug 19, 2016 6:12 pm

With the motor you have I wouldn't go down in ratio. Since you have a bigger heavier boat the prop and torque roll is not as important as it is to us Florida guy's. So keep the torque multiplication but increase tip speed in other words make that prop a 84 or 86 inch and that would be a great combo for YOUR APPLICATION!!!!
THE PROOF IS IN THE PROP!

"If you copy someone you will only achieve what has already been done."

http://waterthunder.com/
321-508-5316

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Fri Aug 19, 2016 6:34 pm

I could go to 82 inch and then I'm out of room for the pancake cage. I can make a new cage but why not just increase the prop speed by lowering the ratio? More prop speed means more thrust. I still feel like I'm missing something. Why do people use the 2.38 instead of 2.68?
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
OneBFC
Southern Airboat Member
Posts: 390
Joined: Tue Sep 11, 2012 1:04 am

Re: Does NGR prop like pitch or RPM?

Postby OneBFC » Fri Aug 19, 2016 7:14 pm

Why do people use the 2.38 instead of 2.68?


If your engine max HP is below 5400 or so, a 2.3 or so makes sense.

If you make more HP above that then a 2.68 or so starts making sens.

Most naturally aspirated engine like to spin around 5800 to 6200 to make their power. Large displacement engines are no exception exception there are some large displacement options like BBC and Cadillac that are built to run lower RPM and those are used direct drive or with lower ratio 1.5 to 2.12 reductions.

It is basically matching your engine HP and torque curve to a propelle and it's torque and rpm needs for a desired thrust.

If you look at some of my recent posts I link to an example of what a prop torque curve vs engine curve looks like based on my own real world tests.

This ALWAYS spurs a long discussion about torque vs Hp vs prop and engine types. At the root however, x prop will require y torque at z RPM when mounted in a boat. Every boat will generate different numbers based on cage and hull design.

A restrictive airflow to the prop due to gage design will result in needing more pitch to generate the same thrust as a prop outside of a cage or in a cage with less restriction.

"Setup" as is often said, is the most important thing.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400hp Ecotec, 12x7.6 DBDO, 4B Falchon, 2.3 OX,70+mph,10mpg,water = purely optional
Life begins at 2 BAR, Just a good ole boy

CarMotorBarge
Site Supporter - I
Site Supporter - I
Posts: 707
Joined: Thu Jul 14, 2011 8:32 pm
Location: Lake Harney Woods

Re: Does NGR prop like pitch or RPM?

Postby CarMotorBarge » Fri Aug 19, 2016 10:20 pm

Des Moines Boater wrote:I could go to 82 inch and then I'm out of room for the pancake cage. I can make a new cage but why not just increase the prop speed by lowering the ratio? More prop speed means more thrust. I still feel like I'm missing something. Why do people use the 2.38 instead of 2.68?


It is easier to get a hub one size larger than it is to change the gear ratio. Might be able to borrow the hub for free and see if it does better. 8) Because you are pitched at 3 already, the longer hub will give you more static thrust. However, you will probably loose top end speed because more blade area will cause increased drag. It is all about trade offs. :violent1:
14x7.5 Al David hull with 14 inch transom
419 CI Horsepower Barn LS3 with 2.68 Rotator soft drive swinging 4 blade 83.5" R
GTO Rigging and B&S Tilt Trailer
Member of Seminole Airboat Club

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Sat Aug 20, 2016 9:20 am

Right now I cruise at 35 to 36 mph at 3600 rpm. At 4000 I'm at 40 mph. At 4000 rpm's the prop is spinning 1481 rpm's. With a 2.37 gearbox I could spin the prop 1481 rpms with the engine only running 3511 rpm's.
It looks to me that a 2.37 gearbox would keep the same cruise and lower my engine rpms by 500.
Am I missing something?
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

SWAMPHUNTER45
Site Supporter - III
Site Supporter - III
Posts: 1950
Joined: Thu Nov 21, 2013 11:38 am
Location: Naturecoast, Florida

Re: Does NGR prop like pitch or RPM?

Postby SWAMPHUNTER45 » Sat Aug 20, 2016 9:38 am

If I understand Dave's comment his experience would suggest you leave the current ratio but get a bigger hub or longer blades to gain tip speed as a factor. His advice seems solid.

User avatar
OneBFC
Southern Airboat Member
Posts: 390
Joined: Tue Sep 11, 2012 1:04 am

Re: Does NGR prop like pitch or RPM?

Postby OneBFC » Sat Aug 20, 2016 10:18 am

Pretty simple, does your engine produce enough torque at the lower RPM to spin the prop the same RPM?

The prop requires a set amount of torque to turn the RPM it is turning that gives you your stated cruise speed.

If your engine does produce enough torque at the lower RPM, then you will have less "snap" no matter what because there will be less excess torque than you had before. So, you would experience a slower rate of engine RPM gain. If you go from a 2.68 to a 2.38 you will give up available prop shaft torqe. So, don't forget to take that into account as well. 100 ft-lb x 2.68 = 268 ftlb. 2.38 results in 238 ftlbs, 30 less. You could very well end up with not enough torque available and you will then have to remove pitch.

I know it is a pain to search for posts, but I just recently posted about this and provided really easy to see data for how and why things work (for one engine, propeller and boat at least).
-Russ
-----------------------------------
The only thing stopping you is FEAR
400hp Ecotec, 12x7.6 DBDO, 4B Falchon, 2.3 OX,70+mph,10mpg,water = purely optional
Life begins at 2 BAR, Just a good ole boy

User avatar
Deano
Site Supporter - V
Site Supporter - V
Posts: 4039
Joined: Thu Jan 06, 2005 11:16 am
Location: Inverness, FL

Re: Does NGR prop like pitch or RPM?

Postby Deano » Sat Aug 20, 2016 10:28 am

What you are missing is that changing the ratio, you are giving up needed torque to turn the prop.

If you hypothetically have 450 ft/lbs at the crank, with your current gear you have 1215 ft/lbs to turn the prop. If you change the gear to a 2.37, you will only have 1066 ft/lbs at the prop. Now, while 144 ft/lbs may not look like much, realize that is giving away over 12% of your available torque. If you have more torque than 450 ft/lbs, the amount of the net decrease would be even more dramatic.

If you keep your current gear, you have the same amount of torque available to the prop.
Using a larger hub will increase the tip speed to better utilize the strong part of the prop's power band.

What they all (Dave, OneBFC, CarMotorBarge, & Swamphunter) are trying to tell you is that changing your gear ratio is the wrong means of increasing your tip speed.
"The suppression of uncomfortable ideas may be common in religion and politics,
but it is not the path to knowledge; it has no place in the endeavor of science."
- Carl Sagan

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Sat Aug 20, 2016 1:30 pm

I understand the torque multiplier but at some point propeller speed has to come in somewhere. Why does anyone use the 2.38 instead of the 2.68? Also, if the 2.68 is best all around, why not a 3.0?

My boat came with a 2.0 gearbox and a 78x48 wood prop. Set the boat on the ground and it would go anywhere you pointed it. I didn't like the loud wood prop and the gearbox sounded like a rock crusher. I sold my 13 foot Laser hull with a 220 gpu and used the money to get a new Ballistic Box and the 3 blade NGR prop. I do like how quiet the box and prop are.
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
OneBFC
Southern Airboat Member
Posts: 390
Joined: Tue Sep 11, 2012 1:04 am

Re: Does NGR prop like pitch or RPM?

Postby OneBFC » Sat Aug 20, 2016 4:01 pm

Brother we are telling you why other people use different ratios, you just aren't understanding from what we have typed about it. I don't know how else to explain it other than look at some of my recent posts, one of them had a link to spread sheets with graphs that will paint the picture graphically for you.

It can't be said any other way than what we have said here unfortunately. It's a darn shame that props are so complex. If we had reliable data from the manufacturers we could make better decisions.

Good luck to you. I think you have gotten really solid advice in this thread and have multiple options available to you yet.
-Russ
-----------------------------------
The only thing stopping you is FEAR
400hp Ecotec, 12x7.6 DBDO, 4B Falchon, 2.3 OX,70+mph,10mpg,water = purely optional
Life begins at 2 BAR, Just a good ole boy

User avatar
Des Moines Boater
Site Supporter - V
Site Supporter - V
Posts: 1401
Joined: Mon Sep 05, 2005 2:24 pm

Re: Does NGR prop like pitch or RPM?

Postby Des Moines Boater » Sat Aug 20, 2016 4:11 pm

No problem Onebfc. I'll stick with the 2.7 and just add a little more pitch. How come you have a 2.3 on yours? Under what conditions is a 2.38 a good choice? Just curious.
13' 6 Lazer, 383 SBC 425 hp, 2.7 Ballistic, 3 blade 80 NGR

User avatar
kwanjangnihm
Site Supporter - IV
Site Supporter - IV
Posts: 1131
Joined: Sat Mar 30, 2013 8:23 pm
Location: Bartow FL

Re: Does NGR prop like pitch or RPM?

Postby kwanjangnihm » Sat Aug 20, 2016 4:59 pm

Different hubs can make the NGR 80"-84".

CM guys always need a few more inches to perform better!! :toothy7: :stirpot:
" I don't care who you are back in the world, you give away our position one more time, I'll bleed ya, real quiet. Leave ya here. Got that? "


Return to “Prop Talk”

Who is online

Users browsing this forum: boatair and 2 guests