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

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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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When

I don't get the thing about fixed props being better around lobster pots, I believe that a folding prop would let the lines (and pot) slide by where a fixed prop might catch it?
When you hit one under power, or floating line, they can for more fragile than a fixed prop. Been there....$$$$$$$$. As much as I'd prefer to sail 100% of the time in Maine that is not always possible with zero wind days and 3 knots of tidal current against you you do use the iron genny..

If I was racing my own boat I would probably own a Max Prop but I race OPB's. IIt would take me a week of hauling stuff off to get my boat to race weight...:D I now use a Campbell Sailor, and while certainly slower, the few seconds per mile lost vs. a folder/featherer just means a more enjoyable sail...
 

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Oh, and btw... you're right on the J boat Martech's, (my bad). But I know several J boat skippers that still set the prop shaft orientation even though it's a folding prop.
But they do this so the bottom blade does not flop down and cause drag not necessarily to align it behind the keel.. If you align it vertically the blades do not flop open at low speeds..
 
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