Half a croissant, on a plate, with a sign in front of it saying '50c'
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Sweating Propellors

Traction control for boats
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Porous propellors that exude a wetting solution to better attach the prop to the water, reducing cavitation, particularly when first getting up to speed. Probably useful for slow turning props, like a submarine. May also quiet things down.

The wetting solution could just be water, but adding a little eco-friendly soap solution would likely make it more effective.

This idea isn't original, I borrowed it from Dolphins who do excrete a wetting solution from their skin to reduce drag.
bristolz, Nov 13 2001


       A few years back I saw a prototype aircraft wing that had air nozzles on the leading edge through which air was blown. The aim was to reduce stall speed by keeping the flow of air smooth across the wing.   

       I can't see a reason why this technology can't be applied to a propeller - as long as you can make a rotational coupling.
st3f, Nov 13 2001

       But won't reducing the drag of the propeller also make it less efficient at pushing water? That is, won't the prop slip/slice through the water and apply less directional force?   

       This might make more sense if we applied it to the hull of the sub or boat instead of the propeller
phoenix, Nov 13 2001

       Aaauuugh! Please forgive me Phoenix, I accidently deleted your last anno. I'm sorry.
I wasn't envisioning it as a flat plate but as a normal looking propellor that had a permeable region, perhaps on the advancing edge of the blades, that liquid could be forced through.

I was imagining that the wetting solution would need to be pumped out at a pretty decent rate for it to be effective. With the fluid pressure high enough (and since it would be hydraulic the pressure could be very high) the material porosity would effectively disappear.
bristolz, Nov 13 2001

       I don't know how well a 'porous' one would work, but it shouldn't be too hard to put in channels that picked up water, maybe from farther forward on the prop shaft, and ran it through little slots or something. Would probably work even better with a bit of surfactant. Waterproof bread for you...
StarChaser, Nov 15 2001

       You know, it's funny . . . . I really thought this idea would get more response than it has. It had been bubbling in my head since early summer, when I was vacationing in the presence of many marine craft and watching, and listening, to their behavior as they accelerated. I guess that length of time under consideration is not proportional to greatness of idea. Ah well, it was a shot.
bristolz, Dec 01 2001

       Most of my ideas are like that. I think it's all a matter of timing (especially with the old interface). It was pretty easy to get swept off the 'recent 3' page, and few people check the 'new' ideas link.
phoenix, Dec 01 2001

       I don't bother with the 'recent 3' page...I do like the idea, bristolz...I think the problem might be that pretty much everybody has posted what they know...
StarChaser, Dec 01 2001

       I could be wrong but isn't that why golfballs have their little knobby bits?
po, Dec 01 2001

       Passing more easily because a disrupted boundary layer increases turbulence directly next to the ball surface, which in turn disrupts, and reduces, the low pressure wake behind the ball. The reduction in the wake is where the reduction in drag comes from.
bristolz, Dec 01 2001

       yes I said all that but it got deleted somehow.
po, Dec 01 2001

       Ooops, sorry. I must have deleted it somehow. Good thing I remembered what it was you had written.
bristolz, Dec 01 2001

       UnaBubba: "they're".   


       Putting the dimples on a sub prop might make it work more efficiently, but probably at the expense of noise, which submariners hate.   

       I wonder if a prop made entirely out of soap would work well <until it dissolved away, of course.>
StarChaser, Dec 01 2001

       too kind bristolz, what a lady, but it was what UB said as well, did you delete that?
po, Dec 01 2001

       Starchaser, is that a rugby prop?
po, Dec 01 2001

       Ya got me there, po.
Hah! I love the bar soap propellor idea.
bristolz, Dec 01 2001

       "Aye, tis Nuclear Spring. Tis green on the outside, and when you cut it open, glows green on the inside!"   

       Po, what's a rugby prop?
StarChaser, Dec 02 2001

       don't know - ask UnaBubba
po, Dec 02 2001

       Ah, an Ook. "Strong like bull, smart like tractor."
StarChaser, Dec 02 2001

       Well, you can actually make a soap propellor for small toy boats. A little bit of soap will repel water enough to push the boat through the water. Try it some time.   

       A dimpeled propellor would actually cause more cavitation, which would cause more noise... and more damage to the prop, leading to more dimpling, this time unintentional. I suppose with very fine dimpling such as the sharks, this might be different.   

       As for reducing noise, the Navy has done far more than just research. In fact, I'd hazard a guess that they've more or less baked this idea. Not entirely sure how much of it I can explain, or actually discuss, but on my clunky old surface ship, they had a hollow propellor shaft that pumped air out near the propellor. The expanding bubbles of air cut down on cavitation, and therefore on noise, and also increased the life of the propellor.   

       I don't think they came off of the propellor itself though, as that appeared to be of solid brass.
ye_river_xiv, Aug 21 2006

       i imagine those props would be made of bronze, not brass... (as brass is a zinc alloy, and zinc tends to dissappear in salt- water.)
jallum, Sep 16 2006

       I would think that you'd want a water-repelling effect on the leading surface of the propeller, and a wetting effect on the trailing surface.   

       I would also hope that either of these effects could be achieved using permanent coatings, chemically bonded to the propeller surfaces.
goldbb, Apr 14 2010

       Wow, a [bristolz] idea from the turn of the century (tears).   


       " Strong like bull, smart like tractor "
normzone, Apr 15 2010

       Unfortunately, I am years too late, but I fear this idea won't achieve its goal. Even if the water sticks to the hydrophilic propeller, what stops it from cavitating a millimeter from the interface?
notexactly, Jan 21 2018

       Hydrogen bonding ?
8th of 7, Jan 21 2018

       Cobalt annealing?
hippo, Jan 22 2018

       //Sweating Propellors// Ah, so not a term for extreme pilot panic, than?
MaxwellBuchanan, Jan 22 2018


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