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Old 06-03-2010, 07:41   #16
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Originally Posted by skipmac View Post
I read an article some years back that published their results on sailing with prop locked vs freewheeling. Their conclusion was the freewheeling prop generated higher drag. Freewheeling apparently builds a ball of water spinning with the prop that is pulled along with the prop creating more drag than the non spinning blades of the prop alone.

With an airplane propeller I believe feathering involves turning the edges of the prop towards the wind and the prop does not spin at all. Of course presenting the edge of the blade to the air stream will result in the lowest drag. Feathering boat props would do the same.

For me, wear or other issues aside, I like to stop the shaft from freewheeling because most of my boats have been aft cabin with the prop under my bunk and the spinning shaft is noisy.
WOW. That was brilliant! Wonder where I read that before...
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Old 06-03-2010, 08:00   #17
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WOW. That was brilliant! Wonder where I read that before...
Darn. Guilty of not paying attention, again.

But in my defense, I do agree that I did state the facts more brilliantly.
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Old 06-03-2010, 08:04   #18
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[QUOTE=skipmac;415029
But in my defense, I do agree that I did state the facts more brilliantly. [/QUOTE]

I agree! Great minds...
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Old 06-03-2010, 08:10   #19
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Originally Posted by Hampus View Post

Actually, the prop creates more drag if it's spinning freely, so the boat will move faster if the prop is locked.

/Hampus
What do you base your opinion on?

I base mine on:

- Segeln's article and testing of fixed/feathering locked/freewheeling props,
- Yachting Monthly's article on feathering vs. fixed props. (I believe 2009),

I do not claim to be right, but I believe they found the locked prop to create twice the drag of the rotating one, e.g:

http://www.propelspecialisten.dk/dow..._test_2008.pdf

I know there has been research that yielded contrary results and also some sound arguments towards something like - ".. with some prop speds it is less, with others, it is more drag ...". E.g, I like this passage, and especially the sketch drawing:

http://www.docstoc.com/docs/25357412...PROPELLER-DRAG

Anyway, it is so easy to test in real life, on a real boat. So, when does YOUR boat sail faster - when the shaft is locked or when free-wheeling?

???
b.
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Old 06-03-2010, 08:46   #20
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Back when I had a fixed prop I did extensive testing to see whether I sailed faster with the prop locked or freewheeling, including a 20nm run where I alternated back and forth every mile, timing the deltas. I came to two conclusions: first, I couldn't measure the difference in actual sailing conditions on my boat; second, I bought a folding prop.
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Old 06-03-2010, 20:56   #21
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Gooo MaxProp. Sure glad the P. O. sprang for it........
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Old 06-03-2010, 21:58   #22
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You can also watch this video..

Quote:
Originally Posted by barnakiel View Post
What do you base your opinion on?

I base mine on:

- Segeln's article and testing of fixed/feathering locked/freewheeling props,
- Yachting Monthly's article on feathering vs. fixed props. (I believe 2009),

I do not claim to be right, but I believe they found the locked prop to create twice the drag of the rotating one, e.g:

http://www.propelspecialisten.dk/dow..._test_2008.pdf

I know there has been research that yielded contrary results and also some sound arguments towards something like - ".. with some prop speds it is less, with others, it is more drag ...". E.g, I like this passage, and especially the sketch drawing:

WHAT ABOUT PROPELLER DRAG

Anyway, it is so easy to test in real life, on a real boat. So, when does YOUR boat sail faster - when the shaft is locked or when free-wheeling?

???
b.
I made this test jig and video to satisfy my own curiosity. With a fairly standard Michigan Wheel 3 blade 16X12 the drag when locked was a LOT more than when allowed to freewheel..

MIT, an the University of Strathclyde also have published white papers and also concluded that a locked standard sailboat prop creates more drag.

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Old 07-03-2010, 01:05   #23
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[QUOTE=Christian Van H;414000]Wait...you had damage from a Borg Warner transmission freewheeling? Wierd, the manual states that its fine...please elaborate.

Christian, I had a Paragon box which is very similar to the old Borg Warners. The box got very hot after a couple of days free wheeling and we started smelling something very hot. The bearings had just been replaced a few months earlier, but now we seemed to have some play in it again. We had to motor for over a day to get over the top of Madagascar and into Mayotte. Once there we begin checking out the transmission again noticed the fluid was off colour and we had a slow leak in the seal. The box wasn't dead but it was hurting a bit from the extra wear and the box never got as hot as it did that day even when the engine has run solid for 48 hours. That is when I was told to use a pipe wrench and did until I could afford my MaxProp.

Cheers

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Old 07-03-2010, 02:54   #24
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Quote:
Originally Posted by barnakiel View Post
What do you base your opinion on?

I base mine on:

- Segeln's article and testing of fixed/feathering locked/freewheeling props,
- Yachting Monthly's article on feathering vs. fixed props. (I believe 2009),

I do not claim to be right, but I believe they found the locked prop to create twice the drag of the rotating one, e.g:

http://www.propelspecialisten.dk/dow..._test_2008.pdf

I know there has been research that yielded contrary results and also some sound arguments towards something like - ".. with some prop speds it is less, with others, it is more drag ...". E.g, I like this passage, and especially the sketch drawing:

WHAT ABOUT PROPELLER DRAG

Anyway, it is so easy to test in real life, on a real boat. So, when does YOUR boat sail faster - when the shaft is locked or when free-wheeling?

???
b.
I would like to say common knowledge and laws of physics but I'd be wrong I googled and found lots of contradictory information. Someone even claimed that the propeller drag while freewheeling or not was dependant on the shape of the hull. Eventually I looked to the bookshelf and brought out "Principles of Yacht Design" by Lars Larsson and Rolf E Eliasson.

It appears that you and Maine Sail are correct. Some information from the book:
"The propeller resistance while sailing may be estimated using the frontal area of the propeller and some suitable drag coefficient." - No news there

"If the propeller is completely free to rotate its resistance is reduced to only about one fourth of that of a locked propeller" - Now, the prop isn't completely free to rotate since there is friction in bearings and stuff. But I think it's safe to say that the drag of the freewheeling prop is less than that of a locked prop and somewhere between 1/4 and 1/1 of the drag of the locked prop, depending on the amount of friction.

The book also sais that the resistance of a folding prop is less than 5% of the fixed and locked one.

An example in the book with calculations for the yacht YD-40 states that, doing 6.8 knots upwind, the drag from the locked fixed prop will be 460N, which would slow the boat by 0.8 knots. A completely freewheeling prop with no friction (i.e. an ideal tranny) would slow the boat by 0.2 knots and the folding prop by 0.04 knots.

I learned something today too

/Hampus
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Old 07-03-2010, 03:48   #25
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I've thought of locking mine in some rivers. The St johns on certain tides would have the prop spinning at anchor.
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Old 07-03-2010, 06:26   #26
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I made this test jig and video to satisfy my own curiosity. With a fairly standard Michigan Wheel 3 blade 16X12 the drag when locked was a LOT more than when allowed to freewheel..
As usual Maine Sail, you have done a great job there! Couple of questions. It was hard to read the GPS at times, can you remember the difference in top speed between locked and unlocked? BTW, I had a blast just riding around with you in your dingy in a Maine harbor...I feel like I should buy you a beer now! Where will you take us next?

BTW, I seem to have been wrong. Fixed drags more than free to spin. Thank you Hampus for starting this thread. This sounds like a good bar bet from now on...
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