Reply
 
Thread Tools Search this Thread Display Modes
 
Old 09-20-2017, 10:56 AM   #1
Guru
 
fryedaze's Avatar
 
City: Solomons Island Md
Country: USA
Vessel Name: Fryedaze
Vessel Model: MC 42 (Overseas Co) Monk 42
Join Date: Sep 2011
Posts: 1,284
New Props

My old prop blades were very thin and could be flexed with your thumbs. I purchased new DQX four blade props from Michigan Wheel to replace my three blade props. I went from 25X27 three Dyna to 26X24 four blade DQX. The new props shook the boat on sea trials. They came with a computer run out sheet that indicated they were with in the tolerance MW sets. Had to re-haul boat and send them out to be tuned. I have attached the computer scans. The original MW scan and the Millers Island before and after scan.
Sharing to help the next guy out
Attached Files
File Type: pdf 2017 Miller Island prop scans.pdf (1.00 MB, 65 views)
__________________
Advertisement

__________________
Dave Frye
Fryedaze, MC 42 (Monk 42') 1989 Overseas Co
http://mvfryedaze.blogspot.com/
fryedaze is offline   Reply With Quote
Old 09-20-2017, 11:03 AM   #2
Guru
 
Ski in NC's Avatar
 
City: Wilmington, NC
Country: USA
Vessel Name: Louisa
Vessel Model: Custom Built 38
Join Date: Jan 2014
Posts: 5,311
My prop guy wants to scan and tune all new props that come through his shop. He claims that after casting and machining, the material "creeps". I'm not sure about that, but I follow his advice.

Did that get rid of your shake? How do you like them?

I like the DQX. Half tempted to replace my old skool three blade with DQX as I have a fair amount of prop noise at higher speed.
__________________

Ski in NC is offline   Reply With Quote
Old 09-20-2017, 07:12 PM   #3
Guru
 
fryedaze's Avatar
 
City: Solomons Island Md
Country: USA
Vessel Name: Fryedaze
Vessel Model: MC 42 (Overseas Co) Monk 42
Join Date: Sep 2011
Posts: 1,284
Quote:
Originally Posted by Ski in NC View Post
My prop guy wants to scan and tune all new props that come through his shop. He claims that after casting and machining, the material "creeps". I'm not sure about that, but I follow his advice.

Did that get rid of your shake? How do you like them?

I like the DQX. Half tempted to replace my old skool three blade with DQX as I have a fair amount of prop noise at higher speed.
The 4 blade is smoother than the 3 blade. For the last 7 years I have always felt a little vibration in the wheel above 1400 rpm. Now I feel nothing the whole way to WOT.
fryedaze is offline   Reply With Quote
Old 09-20-2017, 07:40 PM   #4
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 16,005
The 4 blade is about the same level of vibration as the 3 blade. However a typical 3 blade replacement for a 4 blade would have greater diameter. That would bring the tips of the blades closer to the hull and could cause considerable vibration.

If there's plenty of clearence there should be very little vibration difference between the 3 and 4 blade props. Probably un-noticable on most boats or by most people. Which one you use should be predicated on other variables like power applied, prop clearence, gear ratios ect. I changed props on Willy awhile ago and had plenty of clearence so I could easily have bought a new 4 blade. After looking into it I bought a 3 blade. The big advantage the 4 blade over the 3 is the ability to absorb and effectively apply power. This is however just my opinion.
__________________
Eric

North Western Washington State USA
Nomad Willy is online now   Reply With Quote
Old 09-20-2017, 08:11 PM   #5
Guru
 
fryedaze's Avatar
 
City: Solomons Island Md
Country: USA
Vessel Name: Fryedaze
Vessel Model: MC 42 (Overseas Co) Monk 42
Join Date: Sep 2011
Posts: 1,284
Quote:
Originally Posted by Nomad Willy View Post
The 4 blade is about the same level of vibration as the 3 blade. However a typical 3 blade replacement for a 4 blade would have greater diameter. That would bring the tips of the blades closer to the hull and could cause considerable vibration.

If there's plenty of clearence there should be very little vibration difference between the 3 and 4 blade props. Probably un-noticable on most boats or by most people. Which one you use should be predicated on other variables like power applied, prop clearence, gear ratios ect. I changed props on Willy awhile ago and had plenty of clearence so I could easily have bought a new 4 blade. After looking into it I bought a 3 blade. The big advantage the 4 blade over the 3 is the ability to absorb and effectively apply power. This is however just my opinion.
My understanding is that with the change to 4 blade from three you keep the diameter and drop the pitch 1 to 2 inches. I dropped my pitch 2 inches and the performance is identical throughout all rpm.
fryedaze is offline   Reply With Quote
Old 09-20-2017, 08:45 PM   #6
Guru
 
Nomad Willy's Avatar
 
City: Concrete Washington State
Country: USA
Vessel Name: Willy
Vessel Model: Willard Nomad 30'
Join Date: Oct 2007
Posts: 16,005
fryedaze,
That sounds about right.
Gotta balance hp, blade area, #of blades, pitch and rpm.
All the above needs to match your hull and weight.
__________________
Eric

North Western Washington State USA
Nomad Willy is online now   Reply With Quote
Old 09-24-2017, 07:06 AM   #7
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 19,650
"the performance is identical throughout all rpm."

Is the fuel burn much higher?
FF is offline   Reply With Quote
Old 09-24-2017, 07:21 AM   #8
Guru
 
fryedaze's Avatar
 
City: Solomons Island Md
Country: USA
Vessel Name: Fryedaze
Vessel Model: MC 42 (Overseas Co) Monk 42
Join Date: Sep 2011
Posts: 1,284
Quote:
Originally Posted by FF View Post
"the performance is identical throughout all rpm."

Is the fuel burn much higher?
Man I hope not. It will take me a few fill ups to figure out consumption. I do not have fuel flow gauges.
__________________
Dave Frye
Fryedaze, MC 42 (Monk 42') 1989 Overseas Co
http://mvfryedaze.blogspot.com/
fryedaze is offline   Reply With Quote
Old 09-24-2017, 08:28 AM   #9
Art
Guru
 
Art's Avatar
 
City: SF Bay Area
Country: USA
Vessel Model: Tollycraft 34' Tri Cabin
Join Date: Feb 2011
Posts: 9,541
I was taught:

Less blades makes prop more efficient regarding "screw-through" water.

Also taught, in trade off:

The more blades of a well tuned prop then the less chance for vibration

In addition:

If there were a way to correctly balance a one bladed prop that would be the most efficient.

So:

Three blade props offer best of both worlds regarding screw-through efficiency and reduced chance for vibration.

And:

I've always wondered, seeing as [evidently] less blades = most efficiency... why IB, direct drive pleasure cruisers don't employ two bladed props. I'm sure with today's technology two blade props can be tuned to the finest of tolerances.

Therefore:

Currently, I'm sticking with my twin three bladers. Good push and no vibration.
Art is online now   Reply With Quote
Old 09-24-2017, 01:11 PM   #10
FF
Guru
 
FF's Avatar
 
Join Date: Oct 2007
Posts: 19,650
Way back small aircraft could get a single blade prop.

For boats the hassle is enough blade area may require a larger diameter.

AS the tip clearance is a percentage of the blades diameter a deeper draft might be required.

In smaller sizes 3 blades do fine ,and once the diameter goes over 24-28 inches the price goes WAY up.

32x32 3 blade from Ahoy in LA , expensive but sweet!
__________________

FF is offline   Reply With Quote
Reply

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off





All times are GMT -5. The time now is 10:10 PM.


Powered by vBulletin® Version 3.8.8 Beta 4
Copyright ©2000 - 2019, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2006 - 2012
×