Putting numbers to the feathering v Folding prop debate

Discussion in 'Boat Design' started by Annode, Jun 25, 2020.

  1. Annode
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    Annode Senior Member

  2. jehardiman
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    jehardiman Senior Member

    What numbers.....absolute drag or absolute lifetime cost. A propeller is not selected in a vacuum.
     
  3. Annode
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    Annode Senior Member

    well either would be interesting, but its the drag that the debate is all about. As with so many of these things, the numbers reveal the relevance of the debate. If the locked prop is only 5% more drag than a feathered prop, then it resources might be better spent elsewhere. If that number is 20% then it needs to be addressed.

    With the collective experience of the all the NAs on this forum totaling hundreds of years combined, these numbers should be readily available. This issue has been discussed for decades. Does it really take a boat owner in a dingy with a handheld gps and a kitchen scale to put numbers to this?
     
  4. Annode
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    Annode Senior Member

    <I'm sorry, this quote was stolen and slightly damaged>
    A quote cant be stolen... but it can be re-quoted with editing )
    Looks like someone did that for you...
     
  5. jehardiman
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    jehardiman Senior Member

    If I am poor, are you so witless you cannot come up with a better quote?
    Gods Man! what are you attempting to risk someone's lives with your ideas!
    The MOST IMPORTANT THING ABOUT A NAVAL ARCHITECT IS HIS BELIEVE IN HIS CORRECTNESS!!!!
    YOU ARE GOING TO KILL SOMEONE BECAUSE I TOOK AWAY A QUOTE YOU LIKED?
    CAN YOU NOT JUSTIFY YOUR POSITION!
    HAVE YOU NO METHOD OR MATH THAT CAN HELP YOU!
    YOU ARE A POOR PATHETIC IMITATION OF A HUMAN WHO TRIES TO BE CONCERNED ABOUT HIS FELLOW MAN!
    I wrote the instructions that sent men to their death,....but saved the ship...Please don't compare your pathetic self to me in any way!
     
    Last edited: Jun 28, 2020
  6. Annode
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    Annode Senior Member

    aaah hostility... personal attack... baseless accusations.. inappropriate indignation... outrage...

    yawn... grow up sir. its a quote.

    AS I suspected, your response to this thread asking what numbers I was requesting was nothing more than a veiled jibe to provoke an argument. I not you posting NOTHING of interest or value and certainly NO NUMBERS!

    I find it endlessly interesting that the NA gods blobiate for days, yet say nothing with numbers...
     
  7. jehardiman
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    jehardiman Senior Member

    Why waste it on you?
    Sorry, I have the info you want, but I'm done with this.
     
  8. Annode
    Joined: Aug 2019
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    Annode Senior Member

    oh no... no no no no... im sorry, im so so sorry, I humbly take it all back
    I promise Ill never criticize an NA again - in fact at the mere mention of those two words, I will fall into a kneeling pray position and offer up my repentance
    I agree to forget all my years of experience as an engineer and devote myself to the study of traditional ship design
    I will read every part of every ISO standard including ISO/TC 188 40561:5:1877 47.0028.45.0001(a)(b)(11) Sec. 104.002 4th Leg., ch. 20, Sec. 1, eff. April 20, 1897 subdivision (b) of Section 765
    I promise to weigh and memorize the weight of every object I see from now until my miserable existence ends, including my underpants, and calculate their center of gravity and moment of inertia while in daily , silent, repentant contemplation
    and I will never again imply that you or anyone else in this forum suffers from a grandiose sense of themselves, inflated ego, or delusions of technical mastery capable of parting waters and calming storms for their craft to pass safely, while mere mortals craft, deservedly sink to the depths to be swallowed by Johnas whale itself.
    please
    please
    please give me your numbers... Oh the humanity
     
  9. Ad Hoc
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    Ad Hoc Naval Architect

    Great :)
    See you in about 10 years time then... :D
     
    jehardiman likes this.
  10. Mr Efficiency
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    Mr Efficiency Senior Member

    I'm afraid Annode's anger management classes will occupy too much of his time to be bothering with much else.
     
  11. Squidly-Diddly
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    Squidly-Diddly Senior Member

    I read somewhere (sales brochure for the system in question IIRC) that a mild load (such as low-power generator for topping off the batts) on a freewheeling prop will actually reduce drag, because of how props are designed to push water, not designed to freewheel, and when freewheeling at near zero load causes micro-turbulence since its not the optimal "glide ratio". Not sure how that makes sense since the prop's foil will be "upside down" when shaft is dragging.

    I gotta agree with Annode. There should be at least a "typical" spreadsheet for diff sized typical and common props at a few speeds and their drags in the different modes. Then a boater would at least have SOMETHING to base decisions on. Does anyone even know which way the curves curve?

    I've also looked for basic efficiency of outboard/sterndrive VS inboard w/fixed prop for same horsepower and boat weight but not found anything. Boat manufacturers always publish nice RPMs vs MPG vs MPH spreadsheets for a particular boat.

    I'm surprised there are still lots of guys with large planning boats they buy new or make a change and are beset with mysterious trim issues. Water is always the same density, gravity, etc, so should be easy enough to plug into simulator.
     
    Last edited: Jun 28, 2020

  12. jehardiman
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    jehardiman Senior Member

    I second this.
    Annode, I am sorry, I should not have yelled at you.
    Those who make their living on the sea work in one of the most dangerous, per capita, endeavors on earth. The correctness and integrity of the Naval Architect not only directly effects the mariners lives, but the lives of the Coast Guards and SAR teams who go to aid them. It is not a game you can win with petty theft, or disconnected questions on a forum.
    Realistically, Ad Hoc is correct, there is no question you can ask on this forum that you cannot determine for yourself with 5 to 10 years of diligent study and work. Furthermore, you will gain insight into the limitations to the answer.
    I wish you well in your further studies.
     
    bajansailor likes this.
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