Setting Your Prop for Reduced Drag - SailNet Community
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post #1 of 31 Old 05-02-2009 Thread Starter
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Setting Your Prop for Reduced Drag

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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post #2 of 31 Old 05-02-2009
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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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post #3 of 31 Old 05-02-2009
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Nail Polish or Testor's Model Paint...

the kind that comes in the little glass bottles.

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post #4 of 31 Old 05-02-2009
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center punch

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post #5 of 31 Old 05-02-2009
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Quote:
Originally Posted by backcreeksailor View Post
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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post #6 of 31 Old 05-03-2009
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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.

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post #7 of 31 Old 05-03-2009 Thread Starter
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Quote:
Originally Posted by Maine Sail View Post
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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post #8 of 31 Old 05-03-2009
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Quote:
Originally Posted by backcreeksailor View Post
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/567...ints005670.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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Last edited by Maine Sail; 05-03-2009 at 07:20 PM.
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post #9 of 31 Old 05-03-2009
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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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post #10 of 31 Old 05-03-2009 Thread Starter
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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...

Last edited by backcreeksailor; 05-03-2009 at 07:08 PM.
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