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-   -   Propeller drag test under sail. (http://www.sailnet.com/forums/gear-maintenance/84809-propeller-drag-test-under-sail.html)

RatHatDiver 03-09-2012 09:33 PM

Propeller drag test under sail.
 
Good read.

http://www.catamaransite.com/propeller_drag_test.html

Bradhamlet 03-09-2012 10:06 PM

Re: Propeller drag test under sail.
 
I have heard all day long to lock up the prop. to get better speed but that is not what my gps says or have found out on my own sailing.
Brad

Maine Sail 03-09-2012 10:38 PM

Re: Propeller drag test under sail.
 
That is my test so if you guys have any questions I can answer them....

Minnewaska 03-10-2012 08:35 AM

Re: Propeller drag test under sail.
 
MS, you are a marine mechanical stud. I'm surprised the lady posters here haven't suggested you pose for a calendar.

Way cool test. No questions really, just way cool.

Did you ever do any feathering prop tests? Max-prop procedure is..... neutral, engine off, reverse for a few seconds, neutral. It's a whole different ball game than the purpose of this test. I'm just curious what happens in real life if the feathering prop is left in reverse.

RobGallagher 03-10-2012 10:13 AM

Re: Propeller drag test under sail.
 
Very interesting. Thanks for posting.

Maine Sail 03-10-2012 10:45 AM

Re: Propeller drag test under sail.
 
Quote:

Originally Posted by Minnewaska (Post 843213)
MS, you are a marine mechanical stud. I'm surprised the lady posters here haven't suggested you pose for a calendar.

Way cool test. No questions really, just way cool.

Did you ever do any feathering prop tests? Max-prop procedure is..... neutral, engine off, reverse for a few seconds, neutral. It's a whole different ball game than the purpose of this test. I'm just curious what happens in real life if the feathering prop is left in reverse.

The drag on hem is so minimal that it would be hard to measure differences. MIT has already done it far more accurately than I could and all the folders and feathering props they tested did very well and had minimal drag...

I do have a brand new Flex-O-Fold three blade in my shop that will be replacing a Max on a friends boat. It will be interesting to see if he can tell a difference. This is being done mostly because the Max can still catch pot buoys where a folder can't....

I am installing a two blade Flex-O-Fold on our boat this spring. We'll see how it does. If it vibrates the Campbell Sailor will go right back on & the FOF will be sold........ Our boat has as close to zero vibration right now as any boat I've ever been on so it will be an interesting comparison..

Minnewaska 03-10-2012 11:48 AM

Re: Propeller drag test under sail.
 
Quote:

Originally Posted by Maine Sail (Post 843269)
The drag on hem is so minimal that it would be hard to measure differences. MIT has already done it far more accurately than I could and all the folders and feathering props they tested did very well and had minimal drag......

Sorry, I was unclear. I meant, have you ever tested the impact of leaving a feathering prop in neutral as opposed to reverse on its ability to fold or turn the shaft against the motor. All are told to leave a feathering prop in neutral, although, I've always wondered how important that really is.

CalebD 03-10-2012 02:55 PM

Re: Propeller drag test under sail.
 
Very clever testing as usual and it seems quite conclusive for 3 blade fixed props.
I'm not sure this test answers the same question for my fixed 2 blade prop that is mounted in the dead wood in a cutaway in front of our rudder. With this configuration we can align the prop with the hull theoretically 'hiding' it from being a real drag.
Do you know of any studies that might have been done on fixed 2 blade props with this configuration?
Thanks in advance, as always.

Maine Sail 03-10-2012 03:43 PM

Re: Propeller drag test under sail.
 
Quote:

Originally Posted by CalebD (Post 843368)
Very clever testing as usual and it seems quite conclusive for 3 blade fixed props.
I'm not sure this test answers the same question for my fixed 2 blade prop that is mounted in the dead wood in a cutaway in front of our rudder. With this configuration we can align the prop with the hull theoretically 'hiding' it from being a real drag.
Do you know of any studies that might have been done on fixed 2 blade props with this configuration?
Thanks in advance, as always.

Pretty hard to test that, and I would guess with a two blade the differences would be less "dramatic", but one thing I have learned is that if the prop begins to spin:

1- It is not as hidden as you thought

2- Is taking the path of least resistance

When we had a Cape Dory 27 with two blade even after I aligned it vertical it would still begin to spin...

dabnis 03-10-2012 03:57 PM

Re: Propeller drag test under sail.
 
Quote:

Originally Posted by CalebD (Post 843368)
Very clever testing as usual and it seems quite conclusive for 3 blade fixed props.
I'm not sure this test answers the same question for my fixed 2 blade prop that is mounted in the dead wood in a cutaway in front of our rudder. With this configuration we can align the prop with the hull theoretically 'hiding' it from being a real drag.
Do you know of any studies that might have been done on fixed 2 blade props with this configuration?
Thanks in advance, as always.

Assuming you have fairly constant wind, course and so on, GPS speed seems pretty accurate?

Paul T


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