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1979 C&C 30 Mk I - 2QM15
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Discussion Starter #1
A racing trick that a lot of racer's without folding props use to reduce drag while sailing is to mark the prop shaft so that someone can jump down into the cockpit locker and set the prop to be vertical (in-line with the keel) to reduce drag. (This assumes that you have a 2-Blade prop).

What's something you can mark the metal shaft with that will be resistant to water, oil, etc..., but not something that will damage the metal?
 

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A permanent felt marker pen can last a while, or wrap a peice of light coloured tape and mark that.
 

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Nail Polish or Testor's Model Paint...

the kind that comes in the little glass bottles.

DrB
 

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center punch
 

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A racing trick that a lot of racer's without folding props use to reduce drag while sailing is to mark the prop shaft so that someone can jump down into the cockpit locker and set the prop to be vertical (in-line with the keel) to reduce drag. (This assumes that you have a 2-Blade prop).

What's something you can mark the metal shaft with that will be resistant to water, oil, etc..., but not something that will damage the metal?

You might want to let it spin if you're not on a full keeler..

Prop Drag Test Video (LINK)
 

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More Wear on Tranny

Maine Sail,

I have been told that letting the prop "spin" can put more wear on the tranny, shaft at the SB, and cutlass bearing so one should typically lock in Reverse when sailing to avoid shaft spin.

DrB
 

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1979 C&C 30 Mk I - 2QM15
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Discussion Starter #7
You might want to let it spin if you're not on a full keeler..

Prop Drag Test Video (LINK)
The only problem with that test is that it eliminates the keel and it's effect on the water turbulence in front of the prop. So it doesn't accurately simulate the conditions of drag for a sailboat.

Even without a full keel, a fin keel will still change the water flow in front of the prop. I've never seen a published test, but I know on a race boat, setting the prop has a measurable effect on boat speed. Not something a cruiser is going to notice, but in a race where tenths of a knot can determine the outcome, it makes a difference.
 

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The only problem with that test is that it eliminates the keel and it's effect on the water turbulence in front of the prop. So it doesn't accurately simulate the conditions of drag for a sailboat.

Even without a full keel, a fin keel will still change the water flow in front of the prop. I've never seen a published test, but I know on a race boat, setting the prop has a measurable effect on boat speed. Not something a cruiser is going to notice, but in a race where tenths of a knot can determine the outcome, it makes a difference.


<hr> If you want to keep believing a theory developed when sailboats were racing with full keels and 7 inch wide dead woods with the prop 5" from it, feel free to. You need to know these are not just my findings.

The MIT study done by Todd Taylor & Beth Lurie is also in line with my findings.

The University of Strathclyde Ocean Engineering Department Study finds similarly:
http://strathprints.strath.ac.uk/5670/1/strathprints005670.pdf

And in the May 2009 issues of Yachting Monthly they conducted yet another in depth test where an actual boat was dragged through the water with a strain gauge monitoring loads.

Yachting Monthly - Any Questions: The ultimate propeller test - gallery

Here were their findings:
Prop Drag Results (LINK)

I still suspect there will be doubters who apparently know more than the collective wisdom of MIT, The University of Strathclyde Ocean Engineering Department and the investigators at Yachting Monthly who put this test to "real world" conditions by actually dragging a real sailboat....
 

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Maine Sail,

Is there an actual link to the article from YM? or just the "generic" results an pics available online?

I'd be interested to see the actual results for the individual props them selves, vs just fixed lock vs unlocked prop, or folding or feathering. IE results for maxprop vs kiwi vs fixed etc.

Marty
 

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1979 C&C 30 Mk I - 2QM15
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Discussion Starter #10 (Edited)
No need to get defensive... I just pointed out the very obvious fact that the original test you cited drags a fixed prop through the water in no particular orientation vs. a free wheeling prop while completely leaving out the specific test condition that was in my original post of "vertically aligning" a "2-Bladed" prop with a leading keel and the overall effect on parasitic drag.

The second study you cited (even with the collective brainpower of MIT), also doesn't vertically align a 2-blade fixed prop with the keel. It just tests them in no particularly cited orientation in fixed vs. free wheeling mode.

And the last study you cited only graphed out the drag of 3-blade props that could in no way be aligned with the turbulence pattern of a straight vertical keel.

It's all good info, but it's just not relevant to what I stated in my original post, which was the common routine of racers with fixed 2-blade props to set them so that they're aligned with the keel. If you've got a study that cites that particular condition and shows a negligible, or negative affect on drag, I'd be more than happy to read it. Because I didn't devise or propose the theory, I just know that many racers follow it...
 

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I would SWAG that "MOST" racers today will skip the fixed prop and buy a feather/folding prop vs using a fixed prop in ANY position be it aligned or not with the keel.

The only racers I know that use fixed props are more "Cruiser" oriented than race oriented. Even if I had a true cruiser, I would personally have a non fixed prop. But that is me. I realize MS does like the fixed props, something to do with crab/lobster pots, but I'd still take a feathering/folding if racing on a regular basis. Because the PHRF rating hit, is not as bad as the how much slower you go. Usually more like 12-15 secs a mile with only a 6 sec credit, at least here in the NW US.

Marty
 

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Maine Sail,

Is there an actual link to the article from YM? or just the "generic" results an pics available online?

I'd be interested to see the actual results for the individual props them selves, vs just fixed lock vs unlocked prop, or folding or feathering. IE results for maxprop vs kiwi vs fixed etc.

Marty
Unfortunately you'd need to buy it from them..:confused:
 

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While sailing my Bristol 24 this weekend in light wind; I checked my 2 blade prop alignment and found the mark to be 90 degrees from verticle. I watched my knotmeter as I turned the blade to straight up and down. The speed increased 2/10s as soon as the blade was verticle. I moved it back to sideways, and the speed dropped 2/10s. I have a 2 blade, 12" diameter x 14P bronze prop. The prop is completely enclosed in a cutout behind the full keel.
 

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1979 C&C 30 Mk I - 2QM15
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Discussion Starter #15
I would SWAG that "MOST" racers today will skip the fixed prop and buy a feather/folding prop vs using a fixed prop in ANY position be it aligned or not with the keel.

Marty
I guess that really depends on whether or not dropping $2500-$3000 on a folding prop is a trivial thing for your wallet... But I know plenty of racers that use 2-Blade fixed props. I don't know for sure, but it might have something to do with One Design rules that don't allow you to change anything from the original design on the boat. J-Boats for example (I think) all come with fixed props.
 

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1979 C&C 30 Mk I - 2QM15
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Discussion Starter #16
While sailing my Bristol 24 this weekend in light wind; I checked my 2 blade prop alignment and found the mark to be 90 degrees from verticle. I watched my knotmeter as I turned the blade to straight up and down. The speed increased 2/10s as soon as the blade was verticle. I moved it back to sideways, and the speed dropped 2/10s. I have a 2 blade, 12" diameter x 14P bronze prop. The prop is completely enclosed in a cutout behind the full keel.
This would be in line with what most of the J-105 racers believe the difference is in boat speed with an aligned set prop vs. one that's left to free wheel. (A couple tenths).
 

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...I didn't devise or propose the theory, I just know that many racers follow it...
Most racers, in fact, will have a folding propellor - whose orientation they check/fix (folded blades vertical) while racing to prevent a blade from "falling" open in real slow going.

I think the evidence is quite convincing that a free wheeling prop is less drag than a fixed; however some tranny's won't like it, and I don't like the noise so continue to lock the prop while sailing.
 

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This would be in line with what most of the J-105 racers believe the difference is in boat speed with an aligned set prop vs. one that's left to free wheel. (A couple tenths).
How many J 105 racers are using a fixed prop? As far as I rememebr these boats were delivered from the factory with a folding 15" Martec..? Most that I know use the Martec.

Some thoughts on this. I am not being defensive but I would like to see you win some races.

#1 On my old Cape Dory 27 if I locked the prop behind the keel or locked it not in line at 90 degrees I could decipher NO discernible difference what so ever and tried many times. If I unlocked the prop from in line with the keel it started to spin naturally!

This tells me that even being about 5" behind a rather fat Carl Alberg designed dead wood that the turbulence still did not prevent the prop from wanting to spin on it's own. The prop was taking the path of least resistance naturally. Locking it is causing drag but in this situation it is probably not noticible between fixed and freewheeling much because these boats are already slow and cumbersome when compared to fin keelers.

We know from the the three scientific studies that a locked prop in the standard Michigan Wheel shape causes more drag when locked than if allowed to free wheel. The only exception to this would be a prop like the Campbell Sailor which has virtually no difference between locked and freewheeling due to it's foil shape at least in my tests.

So if a two balde Michigan prop, even hidden behind a large, wide dead wood wants to spin, that tells me the turbulence factor would be next to nil on a fin keeler with the prop four to six feet behind the very hydrodynamically designed fin keel with a very smooth tail end taper.

#2 On my old C-36 I had a two blade fixed Michigan wheel. The boat was faster with the prop freewheeling vs. locked in any position. I experimented with this for a full afternoon with some racing buddies who doubted this. In the end they agreed the boat was faster freewheeling sometimes by as much as almost a half knot in lighter winds when we were not already near hull speed.

All of the boats I currently race on have feathering of folding props.

#3 With that test jig I made the jig accounted for roughly 12 pounds of drag at WOT with no prop attached. The jig bearings were adjusted for friction to closely match that of my CS-36 and the prop began to freewheel at .8-1.2 knots just as it does on my CS.

If you subtract 12 pounds of jig drag from 25 pounds of total drag in freewheeing mode you have a net prop drag of about 13 pounds when freewheeling.

If you subtract 12 pounds of jig drag from 50 pounds of total drag in locked mode you have a net prop drag of 38 pounds when locked.

In this case with a three blade Michigan Wheel the locked prop caused 2.92 times MORE drag than the same exact prop when allowed to free wheel. 38 pounds of drag can also be looked at as 292% more drag than 13 pounds. In this case with a similar friction to my own boat I am causing nearly 3 times more drag when I lock the prop. I still lock the prop when cruising unless of course someone wants a gentlmens run at which point I would unlock it for a quick little impromptu race..

Even if a two blade was only 2 time more drag locked I would still find it next to impossible to believe that any "turbulence" from fin keel, multiple feet away from it, would mitigate a doubling of drag between fixed and locked. With a three blade it was 2.92 times more.

There is a very easy test for this on your own boat. Before you launch mark the shaft with two pieces of tape one at 90 degrees and one vertical. When under sail and with the shaft locked mount a clamp on lever to the prop shaft inside the engine compartment and put a fish scale on it then put the boat in neutral and read the side load. Now repeat this with the prop at 90 degrees and note the readings. The boat should be sailing at the same exact speed to be a fair assessment. I still say to let it freewheel if you have a fin keel. Every ounce of credible scientific data suggests that a freewheeling Michigan Wheel style prop causes more drag locked.

If it wanted to spin naturally on my old Cape Dory 5" from a wide and fat keel.....
 

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My Bristol might not be a fair test, as the prop doesn't want to spin, unlocked, unless I'm doing hull speed. Even then, I can stop the shaft easily with my fingers. My keel is even wider than a Cape Dory. But, I have seen a speed decrease of .1-.2mph when the blade was locked sideways, several times. I've never noticed any difference when the prop was spinning, but I never let it spin for long.
 

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I'd point out that if a keel is big enough and close enough to protect the prop from generating drag, it is also probably big enough and close enough to prevent the prop from working properly... since the water flow to the prop would be too obstructed for it to generate thrust properly, and probably would cause the prop to cavitate a lot.
 
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