Lock that prop: the truth at last

[John Vigor]

I quote from two authoritative sources:

1. Don Casey, one of the best-known experts on boat care and upgrading boats; and

2. BoatU.S. magazine, June/July 2011 issue:

"It may seem counterintuitive, but the drag of a freewheeling prop is significantly more than that of one locked in position because the spinning blades develop lift -- exactly like an autogyro. For this reason, you might want to lock the prop rather than allow it to freewheel."

[Memo to self: I shall not gloat ... I shall not gloat ... I shall not gloat ... ]

John V.

[tartansailor]

I did not wish to raise any demons in criticizing a dedicated chap who built a prop drag experiment and dragged it behind his boat, bit unfortunately ignored turbulent flow hence erroneous conclusions.
Yet critics persisted in clinging to perceived notions and ignored tank tests and calculations that I submitted.
Rest easy John.

Dick

[Joe CD MS 300]

I followed that old thread with interest based more on enjoying the intensity with which the opposing sides felt compelled to obtain some sort of capitulation from the other side rather than in the ultimate truth way back when it was active. I can't remember which side was more persuasive in my mind at this point. My engine manual recommends putting the engine in reverse when sailing so that's what I do. However, as a netural observer I would not consider either Don Casey or Boat Us magazine as the ultimate authority on the subject. Just another of the many experienced persons on one side of the fence or other. Writing books on boat maintenance does not translate into a GED doctorate in fluid mechanics.

[CD-Sailor]

DELETED

[RIKanaka]

[Duncan]

... a GED doctorate in fluid mechanics.

What do you mean when you say "...a GED doctorate..."?

I thought a GED was for when you left school too early, and a doctorate was for when you left too late.

[Joe CD MS 300]

... Writing books on boat maintenance does not translate into a GED doctorate in fluid mechanics.

Be very careful what you wish for. One never knows who's listening.

Where do you see that I was wishing for something? And why would I care who is "listening", what ever that means. This is on the internet so it is available to anyone.

What do you mean when you say "...a GED doctorate..."?

I thought a GED was for when you left school too early, and a doctorate was for when you left too late.

It was a tongue in cheek reference to getting a degree through life experience. The point I was trying to make is that epertise in one area does not assure expertise in another.

[CD-Sailor]

DELETED

[Dick Barthel]

nm

[M. R. Bober]

I think I may change my name--temporarily--to "John Vigor", then I can post some correct information, and try to ease the ignominy associated with this otherwise fine poster.

When I read the opinion in Soundings, I expected another outbreak of "it's like a helicopter, but different", and I was not disappointed. Cold comfort in that.

Let me spin this as a pundit would. I am sticking with the MIT tank testing results, and mighty Casey has struck out, again.

Mitchell Bober
Sunny Lancaster, (Where facts are PROPerly considered.) VA

[John Vigor]

I think I may change my name--temporarily--to "John Vigor", then I can post some correct information, and try to ease the ignominy associated with this otherwise fine poster.

Mitchell Bober
Sunny Lancaster, (Where facts are PROPerly considered.) VA

Dear Mitch:

Do you know what ignominy means? Are you calling me "disgraceful, shameful, or contemptible in quality, behavior or act?" (Webster's dictionary.)

Just because you don't agree with something I said?

John V.

[Loren]

Is this a belief (which means science doesn't matter) or do we look at empirical evidence?

......Don Casey statement with no reference of supporting evidence or scientific investigation at M.I.T. - top science institution in the country. (there is other science to support freewheeling also)

......or just pick a story and stick with it.


Loren

[Loren]

http://www.anything-sailing.com/showthr ... sting-Data
6) The difference between fixed and freewheeling was LARGE so a pound or two here or there means very, very little. Average drag at WOT in freewheeling mode was about 20-25 pounds including the test jigs strut. Average drag in fixed mode including the strut was about 45-50 pounds. As you can see .001 differences in accuracy do not matter when trying to answer this question as related to this very, very popular sailboat prop.

MIT study:
http://www.catamaransite.com/files/propeller.pdf
"The conclusion from these calculations is that a substantial reduction in drag, and thus gains in boat speed, can be realized when a fixed pitch propeller is allowed to freewheel."

The study does an in depth comparison of thrust and drag of a variety of props.

Beliefs can be argued - but facts present a problem...

Loren

[M. R. Bober]

I think I may change my name--temporarily--to "John Vigor", then I can post some correct information, and try to ease the ignominy associated with this otherwise fine poster.

Mitchell Bober
Sunny Lancaster, (Where facts are PROPerly considered.) VA

Dear Mitch:

Do you know what ignominy means? Are you calling me "disgraceful, shameful, or contemptible in quality, behavior or act?" (Webster's dictionary.)

Just because you don't agree with something I said?

John V.

John,

Not to put too fine a point on it, but yes. I was attempting to salvage your reputation in a spinning prop world. I would never allow a blind man to walk into heavy traffic without assisting him.

Wouldn't you do the same for me?

Mitchell Bober
Sunny Lancaster, (Where we don't have much heavy traffic) VA

[Maine Sail]

http://www.anything-sailing.com/showthr ... sting-Data
6) The difference between fixed and freewheeling was LARGE so a pound or two here or there means very, very little. Average drag at WOT in freewheeling mode was about 20-25 pounds including the test jigs strut. Average drag in fixed mode including the strut was about 45-50 pounds. As you can see .001 differences in accuracy do not matter when trying to answer this question as related to this very, very popular sailboat prop.

MIT study:
http://www.catamaransite.com/files/propeller.pdf
"The conclusion from these calculations is that a substantial reduction in drag, and thus gains in boat speed, can be realized when a fixed pitch propeller is allowed to freewheel."

The study does an in depth comparison of thrust and drag of a variety of props.

Beliefs can be argued - but facts present a problem...

Loren

Also:

Yachting Monthly dragged boats through the water and reached the same conclusion free spinning = less drag, The University of Strathclyde Ocean Engineering department also studied this with sailboat pros and they too found the same as MIT that free spinning = less drag. Yachting Monthly, MIT, Dave Gerr NA/Westlawn, The University of Strathclyde and others have actually done the critical analysis and not just repeated an age old "wisdom"..



I have also put an open invitation to anyone who still doubts ACTUAL VIDEO PROOF, to come and witness it first hand and perhaps hold the video camera for me. As of yet no takers....

Of course me thinks John is just trying to stir the pot again...