My Redneck preliminary sound testing

[Waterthunder]

My Redneck preliminary sound testing. I have been pushing my higher gear box ratio theories for years now. Every person who has gone to my 2.68 combo has loved it the 2.38 works great too. They are shocked at what a low RPM they cruise the river at less than when they ran a 2 to 1 ratio box However I have been swinging the prop’s at a lower RPM than the prop manufactures are recommending but running a lot more pitch. Present combo is a 2.68 ratio with a 78inch Power Shift turning 5,800 RPM max this gives a prop speed of 2,164 RPM far below the recommended RPM. Here is a break down of the velocities!

Prop Diameter, inches Prop RPM Rotational Velocity, radians/sec Tip Speed, inches/sec Tip Speed, miles/hr New Diameter New Rpm@Constant Tip Speed Reduction Ratio Motor Rpm
78 2200 230.4 8984.7 510.5 78 2200.0 2.68 5896
Funny thing is this set burns up the hill and waxes other boats swinging much more RPM. This is not a theory I have proved it so many times I don’t care to anymore. Anyway here is another plus one of my gear box theory. A customer of mine has a 550HP motor set up this way with mufflers and when he rides all you hear is the gearbox howling, see the gearbox make more noise than a muffled motor or a prop turning at cruising RPM. The noise issue can be resolved but nobody seams to want to do it. Well now I now why but it’s not an issue, it once again reverts back to everyone’s fear of running a high ratio box. Anyway I'm Borrowing a DB meter and will start doing my own sound testing. Then hopefully at the next FWC test I will just show up and see if they will let me participate!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!

 

[jim]

People probably do care, especially in the areas proposing new regualtion. It's simple, if you can't hear the boats there should be no complaints. I think it is probably the $$ involved more that the fear of the high ratio gear.

If you need help with the sound testing, let me know and I'll come over there and help you.

We should make a video of a boat with the quiet prop and mufflers, and post it.

If we could get a prop manufacturer to design a prop to turn even slower, and use an higher gear it might get quieter. It looks like the Maximus is designed for 2200.

5800/3.26=1780 (about)

Jim

 

[stan]

a fellow airboater runs two five blade warp drive propellers stacked behind a 350 with 2.38 rotater turning 4800 on the engine , quite the quiet beast fast and strong on the hill . looks like alot of prop with alot of reduction may be the way to go.

 

[Waterthunder]

Been preaching it for years. However you will hit a point when gearbox efficiencies will over come the torque multiplication value. I did some testing with a 3.26 ratio. I was swinging a huge four blade power shift with ton’s and ton’s of pitch but it didn’t perform as well as a 2.68 with a three blade. The higher gear ratio you run the less efficient the gear box becomes. I do like the slower prop because it produces less sound and when you can swing the pitch you cruising speed is very low and so is your fuel consumption.

 

[stan]

a few years back i played around with a radio shack db meter (not very accurate but better than nothing ) in the run at juniper , checking boats as they came and went the loadest of boats were the aircraft and direct drives with wooden props most reduction boats at that time were a lot lower but none were less than 95 db at a 100' when wfo on the sand. all 2:1 ,2.38 hadn't caught on yet.wish i had a good db meter to loan you thunder i truley believe you can do it.

 

[Waterthunder]

This board is awesome thanks too everyone who has offered help. I now have three test props and a DB meter at my disposal for testing along with some help being offered. I will be doing a DB test and a true thrust comparison between three prop’s along with acceleration numbers and MPH taken at ten foot increments. It looks like the testing will occur around a month from now. As always I will be glade to share all information I find.

 

[marshmaster pat]

Thunder - makes sense with turning more pitch at lower speeds. That three blade wooden prop that exploded got that 14 airgator on step with 2 people and a 0-540 motor turning just at 1500. With one person it would cruise on step (not fast but planed out at 1400 easy). Never really noticed the noise factor that much.

But I have my power shift pitched more that most. I cruise at lower RPMs and that probably means lower noise. However, it also prevents someone from running the engine up to redline. The one drawback I have with more pitch is that coming out of the hole I am slow, and taking off in grass, she has to wind up to get the boat moving, but once she moves, I am at lower RPMs.

It really sounds like you are on to something. Making me wish I had money to play with and look at getting another motor.

Run those tests and let us know.

 

[Anonymous]

This is not a theory I have proved it so many times I don’t care to anymore.....

"Waterthunder's Law"

 

[under pressure]

Hey Thunder, How much are the prop companies paying you to do thier testing for them?????????