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  #11  
Old 09-17-2013
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Re: Prop turns

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Originally Posted by Capt Len View Post
Pricy (2700 $) and don't like driftwood much.Advantage is that they fail completely before the shaft bends.The parts are not interchangeable and after you cut off the end of the shaft to fit the maxi your solid wheel may not have a place for nut and cotter.But you don't have to drag that bucket or lock the shaft. For me it's a write off come tax time and we all know it's about the increased speed.Even on a gaffer.
True, and that's just the 2 blader, correct?.. still and all the reduction in drag is very noticeable under sail, we have a 3 blade so smoothness is even better than our former fixed 2 blade, and reverse is a dream.. so I'd call it a net positive overall.
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Old 09-17-2013
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Re: Prop turns

That price is a 3 blade 21 inch for my 100 hp suzzy, Seattle.I'm getting pretty good at installation and pitch change. pros outweigh cons. Must ease slow thru neutral to in gear.
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Old 09-18-2013
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Re: Prop turns

I loved the a Martec folding prop on a previous boat. They're relatively inexpensive. The boat sails faster and faster is more fun. The difference was more noticeable when cruising; we got where we wanted to go faster.
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Old 09-19-2013
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Re: Prop turns

Does anybody know what the result of the video test was? I don't have access to the magazine and the video only gave the results of the free wheeling propeller.
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Old 09-19-2013
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Re: Prop turns

There's always the first ever in-water sailboat specific prop drag test ever done. I built the test jig and conducted the testing back in the spring of 2009 to get my own answers to a multi-decade question "Does a fixed typical sailboat prop, in water, have more drag when locked or when allowed to freewheel?" .

I conducted this in-water testing well before the Yachting Monthly stuff was likely even thought about. It would not surprise me if they "borrowed" the concept from me.... I could care less because they have a wider audience. I do find it rather cheesy that they would tease you on this and make you buy the article. I published my test for free...

I also have a long standing OPEN INVITATION to any of the old wives tale believers / net-doubters / helicopter theorists etc. to come to Maine, pay for my time and physically got through this testing with me, on video. The only catch is that you A) pay for my time. B) Be willing to publically eat crow on YouTube......

As of yet not a single taker..... To be honest I had NO IDEA which way this testing would land and this is why I spent the time to build the testing jig, because first and foremost I was curious.

Also MIT and the University of Strathclyde Ocean Engineering Department studied this with sailboat props and found exactly what YM and I did.

Prop Drag Test Movie - YouTube



This hinge was designed to allow the leg to move throughout the travel arm needed, less than 1/2".. It was also greased for minimal friction.


The drag assembly was designed so the UHMW friction bearings could be tightened to match the resistance of our sailboats prop shaft shaft. A single nail through the shaft is the only difference between locked and un-locked.


A Harken bearing block was used to reduce/eliminate any line friction.


The test jig:


This was a very simple A/B test with the only difference between locked and free spinning a very small nail. Locked had way more drag...
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Last edited by Maine Sail; 09-19-2013 at 08:34 AM.
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Old 09-19-2013
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Re: Prop turns

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Originally Posted by Maine Sail View Post
Actually it is the locked prop that slows you down..

What position to place your gear in is dictated by the gear manufacturer.

Hurth/ZF = Reverse or Neutral

Kanzaki/Yanmar = Neutral or a shaft brake must be fitted for locking

Yeah, I suppose that I should have mentioned that I have a folder, so locking it helps keep it folded.
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Re: Prop turns

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Originally Posted by Rhys05 View Post
Yeah, I suppose that I should have mentioned that I have a folder, so locking it helps keep it folded.

Exactly, locking a folder creates enough "drag" to close the blades while freewheeling may not...
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Re: Prop turns

Main Sail, that's pretty convincing and I believe you are correct that a free wheeling three bladed marine propeller creates less drag than if it were fixed.

What's driving me nuts is that I know from my own testing that the exact opposite is true of a two bladed aircraft propeller. I've been told that a free wheeling aircraft propeller will have drag equal to the disc area that the prop turns through.

I wonder if it has to do with the disc area of the turning prop vs. the area of the blades?

A fixed aircraft prop covers only a small fraction of the disc area where a three or four blade marine prop probably has more blade area than the disc area.

I wonder if your results would be the same with a two blade marine prop?

Of course I believe it would be better to stop a two blade prop behind the skeg or keel where it sits in already disturbed water.
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Re: Prop turns

Two entirely different mediums and two entirely different speeds. I have actually tested a 16 X 12 two blade and the results were still very much in favor of freewheeling.

Also we can't forget all those two blade folding props that continue to freewheel in neutral, until the split second you add drag by locking the shaft in reverse, at this point they instantaneously slam shut....... Not enough "drag" in neutral for them to close, and they very often continue to freewheel, but when locked in reverse plenty of drag to close them..

I suspect there is a speed and pitch where this would change over but for the average sailboat prop I don't think we see it..
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Re: Prop turns

Back in the late sixties Brian Walker towed a bracketed long shafted gizmo with a prop on the end.It was spring loaded so drag could be ascertained. It included a brake and an alternator. The information was used in his design of a massive dog clutch and pulley power take off on the shaft of his Passing Cloud ,68 ft schooner sailing to NZ and back.I wasn't party to the experiments but Brian was one interesting dude.
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