Fixed vs. Free Wheeling Prop - Updated !

Maine Sail

Maine Sail

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Feb 6, 1998
11,697
Canadian Sailcraft 36T Casco Bay, ME
Preliminary results

Hi Guys,

Some of these posts are actually quite funny.:) A couple of you will be quite surprised when you see the video, though I'm sure you will still argue the methods and .001's, even with full color video staring right on your screen.

I tested the Dumbo Ears prop today and I can assure you the results were not close, and nowhere near a 10% difference. You'll need to wait until I can figure out how to import the video and get it up on the net. For now I'll just let you guys keep arguing & pontificating..;)

I need to warn you the video quality will really suck because I tried to capture the entire run, from locking the prop with the nail to running her up to full rpm, with no pauses. There will be no or very, very minimal edits of the runs so no one can say I edited stuff in or out. The results are what they are.

I made a few changes, one being I moved to a 50 pound analog scale so the results were easier to see.

I think many will be surprised by what I found, I know I was.. Happy arguing and it's actually fun watching the engineer types....;);):D

P.S. I'm warning you I REALLY, REALLY suck at the video camera..!! I hope to have the video up as soon as I can get to it. I've not even watched it yet..
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Engineering 101

Yea Warren, I think it is a pretty silly exercise given that we can make the following observations:

A stationary prop does not heat it's bearings or anything else for that matter
A rotating prop does push energy into its bearings and that energy has to come from somewhere. Geee, I wonder which has more drag?
The basic conservation of energy problem. A no brainer!

For the purist, the stopped prop does heat the water ever so slightly but the "parasitic heating" is going to be really similar in both cases so it factors out.

The Great Roosack predicts that the rotating prop will exhibit more drag.
 
Maine Sail

Maine Sail

.
Feb 6, 1998
11,697
Canadian Sailcraft 36T Casco Bay, ME
Bill Roosa said:
Yea Warren, I think it is a pretty silly exercise given that we can make the following observations:

The basic conservation of energy problem. A no brainer!


The Great Roosack predicts that the rotating prop will exhibit more drag.
Click to expand

Pretty confident statements from someone who has has two engineering studies going against him, including one by MIT, and an article in a UK magazine just this month that supports both MIT and the University of Strathclyde studies.;)

As I said this is getting funny..:)
 
sailingdog

sailingdog

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Oct 22, 2008
3,502
- Telstar 28 Buzzards Bay
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

Looking forward to the video... :) iMovie is your friend... :)
 
Bill Roosa

Bill Roosa

.
Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
Funny!!!, Funny!!!

I'm a us Army Special forces officer and knight of the 5 sided castle quintex!!!!!

By gum this is not "funny" stuff.

These are world changing events you are dealing with and I, for one, am shocked at your casual attitude toward it!!!!!!!!!!!!!!!


Those "dudes" at MIT are all ferries and need a massive shot of testosterone IMHO. They couldn't find a "drag" with both hands and a map!!!!







Oh yea, did I tell you about the airplane analogy?
The glide ratio on an airplane with a stopped prop is higher than the ratio of one with a rotating prop. So a stopped prop airplane can glide further than one that is spinning its internal engine components (conservation of energy) by passing wind over a moving prop!


Think of it this way, if I attached the prop to a generator which would you expect to to produce a greater drag? the one that is pumping 1000 watts into my batteries or the one that is pumping 0 watts?
 
Rick Webb

Rick Webb

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Jun 2, 2004
3,475
Hunter 23.5 Fort Walton Yacht Club, Florida
I can Attest to the Fact The Fact the Spinning Blade Creates More Drag

Enough so that a helicopter may land nearly as soft without a functioning engine as one that does. How this tranlates to the boat prop I dunno sounds like the same thing to me though.
 
Chuckbear

Chuckbear

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Jan 3, 2009
821
Marine Trader 34 Where Ever I am
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

That is all fine and good but a prop spinning in water and a propeller on a plane or helicopter are by no means an equal comparison.
 
Don S/V ILLusion

Don S/V ILLusion

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Sep 25, 2008
7,316
Alden 50 Sarasota, Florida
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

how about this?
For those with fixed props, watch your knot meter when going from fixed to free.
Replicate the result; check your tranny owners manual,
This isn't that complicated...
 
T

tommays

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Oct 2, 2006
1,517
Jboat J24 commack
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

Well

My J24 started the 4hp outboard (it was fully warmed up) when i forget to put it in neutral last summer :)

And even leaving the motor a bit in the water causes massive drag
 
Bill Roosa

Bill Roosa

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Jun 6, 2006
6,990
currently boatless wishing Harrington Harbor North, MD
But we can make it complicated

In fact we want to make it complicated. Since it is easy then anybody can do it. We are trying to raise ourselves (in the eyes of neophyle sailors). how can we maintain our position of superiority above these folks if we don't complicate matters beyond what is necessary? I mean after all sailing is not that complicated as Don has (so dangerously) indicated.

If we are to maintain our position on this BB as the supreme elite then we need to stop indicating that things are "simple" and "you can do it". It is just this kind of stuff that undermines the ruling elite and results in "common folk" being empowered with (gasp) capabilities to solve their own problems.

This kind of thing can not be allowed to continue. We are risking our phony baloney positions on the BB guys!!!!





stopped props have less drag!!!
 
Don S/V ILLusion

Don S/V ILLusion

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Sep 25, 2008
7,316
Alden 50 Sarasota, Florida
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

Bill I'm not sure who "we" is in the first part of your comment but I do know one thing (and suspect you'd agree) - that if I can sail, maintain a boat, keep the batteries alive, keep the topsides sparkling and manage to keep the crew and guests safe, anybody can do it.
I agree with your sarcasm.
 
SeaTR

SeaTR

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Jan 24, 2009
408
Hunter 22 Groton
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

geeezzzz......you boys are havin' way too much fun with this one... Chuckbear's on to something... compare apples to apples, or do the empirical test as Don suggests...
Y'all have a good night firing your salvos.
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

I have always allowed my prop to free wheel. I figure that fixed is half way between free wheeling and idling in reverse.
 
Tom S

Tom S

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Feb 4, 2004
172
Catalina 36mkII Stamford, CT
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

Prediction - Dumbo ears prop has less drag while freewheeling.

There, that pretty much covers the bases.

Now we are all in suspense -please post your results before we explode
 
kloudie1

kloudie1

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Nov 6, 2006
10,019
Hunter 34 Mandeville Louisiana
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

Awwwww MAN.. I have to go off line for a while to look after Mom.. No internet connection .. The suspense is makin’ me crazy! I won't see the results for a while.. I do have some crow ready to eat if that is necessary!
Looking forward to seeing the video, Maine
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,697
Canadian Sailcraft 36T Casco Bay, ME
Video

Video is done but need to save it as a movie file then upload it to You Tube. Should have it up sometime today..
 
Tom S

Tom S

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Feb 4, 2004
172
Catalina 36mkII Stamford, CT
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

Don, I have tried that over and over (watch your knot meter when going from fixed to free) and I have yet to see anything conclusive at all.

I never really see a difference. I think on many of the bigger cruising boats (more than moderately sized) the amount of drag of the prop really makes little difference in the scheme of things. I think the reasons are many, could be slightly stronger or lighter winds for the moment, possibly wave or current action, etc. I think most of us would see a MUCH bigger response in speed with better set sails than worrying about the prop spinning or not. I would dare say the drag on many peoples hull with slime or other growth would be more than the drag on a prop.

In a pure racing boat or a nice slick bottom daysailor in a nice calm consistent breeze day, then I think one might be able to see the difference in speed (freewheeling or locked)
 
Ross

Ross

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Jun 15, 2004
14,693
Islander/Wayfairer 30 sail number 25 Perryville,Md.
Re: Fixed vs. Free Wheeling Prop - Coming Soon !

I switched from a two blade prop to a three blade prop there is a great difference in thrust but I don't notice a difference in carry distance when I shift to neutral.
 
Rick Webb

Rick Webb

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Jun 2, 2004
3,475
Hunter 23.5 Fort Walton Yacht Club, Florida
My Prediction is it is Not a Single Answer

I suspect it is a function of the blade chord ( I guess that would be the term) the RPM and speed. Increase the chord or the RPM you have a larger area that drags through the water you are moving through.
 
Maine Sail

Maine Sail

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Feb 6, 1998
11,697
Canadian Sailcraft 36T Casco Bay, ME
The video is up..

The video is up and the original post has been updated with a link to it..
 
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