[HN Gopher] Sharrow MX-1: Tipless propeller (2020)
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Sharrow MX-1: Tipless propeller (2020)
Author : flybrand
Score : 372 points
Date : 2022-12-12 01:47 UTC (21 hours ago)
(HTM) web link (www.mby.com)
(TXT) w3m dump (www.mby.com)
| csours wrote:
| It does look really cool, but there ain't no such thing as a free
| lunch. More surface area means more drag. More complex shape
| means higher price for the prop and poor reparability.
|
| That doesn't mean it's bad, or that it won't work. It very well
| may have use cases that are not served by simpler propellers, and
| where the price is not a obstacle. For instance, I wonder about
| very large ships where a little bit of efficiency may pay off the
| purchase price.
| [deleted]
| alex_duf wrote:
| I guess if there's more drag but the water is more efficiently
| propelled towards the back it might still be worth it?
| [deleted]
| flybrand wrote:
| I'm planning how to trial a smaller version on our EFoils in the
| spring. For battery power, that bump is huge.
| ri0t wrote:
| Which is exactly what i'm looking at, too. F** any noise
| improvements.
|
| With the smol angry-pixie-driven (very quiet!) harbour pusher,
| i'm just looking at ways to not use up too many angry pixies.
| This one looks promising and can be 3D printed. Original props
| for that one come in plastic only, anyway, which is really
| good! Might've accidentally killed my rudder this year,
| otherwise.
| brk wrote:
| So far in unbiased real world tests the efficiency gains have
| been fairly limited,and. It enough to offset the increased costs.
| Note that I mention unbiased tests. There are some manufacturer
| tests comparing a boat with essentially a wrong prop to the
| Sharrow, and showing impressive results.
| edrxty wrote:
| I wouldn't buy one for a pleasure craft, but even a small
| efficiency gain in ocean freight could turn the industry on its
| head.
| HenriTEL wrote:
| Maybe the tech just does not scale for large propellers (it
| breaks, becomes less efficient or is too complicated to
| maintain). The company has been there for a few years now so
| if there was a real game changer I'm sure they would have
| accelerated much more.
| brk wrote:
| Large container ships already use variable pitch props.
| moffkalast wrote:
| Didn't the US coast guard order a few to test on their larger
| ships? The efficiency gains must be credible for that to happen
| I imagine, though I can't find a good source for that order,
| and I'm not sure where I heard it.
|
| I'm just waiting for someone to make an RC scale injection
| moulded plastic version of it :P
| MichaelZuo wrote:
| "However, extensive sea trials carried out by US website
| boattest.com on the new Sharrow Propeller MX-1 seem to confirm
| all of the above and show efficiency gains of between 9-15% over
| comparable 3-blade propeller designs.
|
| The tests were carried out on a 20ft Bayliner VR5 sportsboat
| fitted with a standard Mercury 150hp outboard engine, comparing
| Sharrow's new tipless MX-1 against two market leading-
| competitors. Not only was it the fastest of the three (41.7 knots
| vs 40.8 knots and 39.0 knots) and the most efficient (4.6mpg @ 32
| knots vs 4.2mpg and 4.1mph), it also planed earlier and
| outperformed them both at every 500rpm increment from idle speed
| to wide open throttle."
|
| Seems like the title is incorrect? The article only claims 9-15%
| mileage improvements along with vibration reduction and handling
| improvements.
| idiotsecant wrote:
| No, it claims 9 to 15% _efficiency_ gains. A more efficient
| machine, with all else being equal, is more powerful at that
| same engine condition.
| MichaelZuo wrote:
| Efficieny gains of boat propulsion translates into mileage
| gains... unless boats work in some non-linear manner?
| idiotsecant wrote:
| Imagine you have a propeller with an efficiency of 50% at a
| particular differential pressure. What happens to that lost
| 50%? It turns into heat. Now imagine you have a fancy new
| propeller with an efficiency of 99% at that particular
| differential pressure. All that energy that you were using
| making heat before is not turning into thrust. Your overall
| engine-propeller system is now twice as powerful at that
| same differential pressure.
| MichaelZuo wrote:
| Okay, and?
| VLM wrote:
| Small sport boats usually operate way above hull speed in the
| the far non-linear region so an extra ten percent thrust will
| result in a far non-linear increase in speed. I'd believe an
| extra 15% of thrust would only make it 2% faster.
|
| Really small boats with really huge engines can push quite a
| bit past hull speed at ultra low efficiency, and that's the
| only numerical stats they're providing in the article, which is
| interesting. I wonder if performance is just as high at low
| speeds, below hull speed, where most cargo ships operate and
| all the marketing greenwashing is occurring.
|
| Hull speed is not "supersonic" but its a similar enough to
| rhyme concept, where the boat has a tough time pushing up or
| thru its own bow wave, sort of, so the max speed of a boat is
| mostly related to its length. Oddly enough the hydrodynamic
| variables all cancel out or whatever such that mostly all that
| matters is wetted hull length for hull speed. You'd
| superficially guess something like hull depth would matter or
| width or shape kind of like the stall speed of an airplane wing
| depends on its shape, but no, ships hull speed almost entirely
| depends on the wetted hull length. Just a weird hydrodynamics
| thing.
|
| Maybe an air craft carrier with 10 times the power could go 5%
| faster, but it would take 100x the power to get an AC carrier
| up on plane like a ski boat.
| ltbarcly3 wrote:
| However engines are roughly linear in displacement vs power
| output. A 15% increase in thrust would mean you can reduce
| the displacement of the engine by 15% and maintain the same
| speed. This would be compounded by the weight savings,
| smaller fuel tank, etc.
|
| However, I think there is a far less than 15% increase in
| thrust, and due to the super-linear loss of efficiency at the
| top end to get a 15% increase in efficiency for the same
| output level might only require a 3% or so increase in thrust
| at that output level.
| AmVess wrote:
| Run it through grass or weeds and then it won't seem so
| innovative. Also, $4300 more than a standard prop means that a
| single trip over an unseen gravel bar will be the first and last
| time anyone uses one of these.
| ri0t wrote:
| Hah. Jokes on you! I'll gladly try using a 3D printed version
| of this on my 600W angry-pixie-harbour-pusher - which they only
| sell overpriced plastic props for, anyway ;D
|
| Btw.: Worst thing: ride backwards and you'll have to tighten
| the mounting screw or risk loss of prop. Best thing: Rudder
| survived hard prop contact with just a few scratches on the
| outer coat \o/
| Gordonjcp wrote:
| I look forward to seeing your HN post in a month's time about
| it.
|
| How Hard Can It Be...?
| serf wrote:
| 4300 is within the sales price range of exotic propellers,
| anyway.
|
| a feathering/folding prop for a 35 foot sail boat is about 3
| grand already, and it's certainly not a single piece of billet.
| The real exotic race-y stuff for that size boat is ~6 grand.
|
| Yes, it sucks to ruin a prop -- but it's almost certainly user
| error 90% of the time; either sucking in boat lines (which will
| lead to a stall and engine mount damage/ prop-shaft damage in a
| majority of cases, not prop damage.), or running aground.
| ri0t wrote:
| Uh, plastic props for my harbour-pusher come in at lousy 45
| bucks. Sometimes, i'm so happy to own a smol boat.
| jpgvm wrote:
| That price was for essentially CNC milled prototypes, I imagine
| if they cast them they would be a fraction of that price.
| ri0t wrote:
| They could offer very customized versions made in an Inconel
| 3d printer.. Wonder if that (economically & technologically -
| is inconel seawater safe??) really makes sense, though.
| serf wrote:
| casting that shape would require some kind of sacrificial
| mold like a sand-casting process. cheaper than billet, but
| not by much unless you're talking big industry scale.
|
| I wonder myself if it's small enough to use a laser-sintering
| print process to build.
| pifm_guy wrote:
| Sacrificial sand moulding is done all the time and is
| pretty cheap:
|
| https://youtu.be/lnHhP_kZ43k
| Gordonjcp wrote:
| Why would you cast it at all, when it's a perfect shape for
| forging the blades and then welding or brazing them
| (depending on the material) to a central hub?
| ISL wrote:
| If the two halves of a mold have some helicity, I suspect
| it is possible to cast such a shape. After all, the water
| also needs to flow through the prop, so too can the halves
| of a mold.
| Oxidation wrote:
| Even if the geometry doesn't quite work out, it's also
| possible you could cast a shape that _can_ be
| "unscrewed" from the mould and then machine a relatively
| thin layer from the outside of the cast part (relative to
| how much you have to machine from a billet). It'll need
| some level of machining anyway.
|
| Binder-jet printing of sand cores is pretty cool too.
| chrisdalke wrote:
| I think it's a pretty cool design but repairability does seem
| like a concern -- Normally you'd take a stainless prop to a
| shop and they'd just weld + grind any small damage but that
| seems more difficult with the geometry of this propeller.
| Gordonjcp wrote:
| I don't see why it would be, unless you bent the blades
| really badly.
| alex_duf wrote:
| I'd love to know a real world figure on improved efficiency on
| cargo ships.
|
| If a "simple" innovation like that can move the needle juste by a
| few percent points on how much fuel we put into the transport
| industry, that's a very sizeable gain from a climate perspective.
| sigmoid10 wrote:
| Not really. The whole shipping industry accounts for 90% of the
| world's transportation of goods, but only 3% of greenhouse gas
| emissions. The problem with big ships is that they burn crude
| oil and create insane amounts of NOx and Sulphur pollution.
| Propellers won't solve that issue, only international
| regulations can. The industry also grows by several percent
| each year, so the best thing a small improvement like this
| could do is counter a few years of growth at best.
| cookieswumchorr wrote:
| well, the emission of all these pollutants should go down
| proportionally if you can save some fuel
| alex_duf wrote:
| Thanks for pointing out it's only 3%. It's much less than I
| had pictured! (I also went to look it up after your comment).
|
| Let's imagine 3% of improved efficiency (they announce
| between 9 and 15%, but let's be conservative) on the 3% of
| the world's emission, that's still almost 0.1% of the world's
| emission saved by only changing the propellers on cargo
| ships. It's still a massive improvement: 31 million tons of
| CO2 saved. At this scale, anything that moves the needle a
| little bit should be taken. But that's by plucking a number
| out of thin air, so I'd love to hear about it in the real
| world and at scale.
|
| Regarding the rest of your message, I agree that the type of
| fuel that is burned is a big problem, but if changing a
| propeller means burning x% less of it, it's a no brainer to
| me!
| awestroke wrote:
| It would actually have the opposite effect. More efficiency
| means lower cost, which leads to higher utilisation
| happyopossum wrote:
| With large shipping, there isn't a lot of underutilization
| - and what there is is not there due to fuel cost.
| Gasp0de wrote:
| So 0.3% of the worlds greenhouse gas emmissions by JUST
| replacing a few propellers doesn't seem significant to you?
| Can you name another measure that would reduce emmissions in
| a similar scale with a comparably low effort?
| DoingIsLearning wrote:
| Commercial and residencial buildings setting their heating
| to 19 celsius or their cooling to 23.0 Celsius.
|
| Haven't checked the maths but energy use in buildings is a
| far bigger chunk of emissions than shipping.
| bearmode wrote:
| Do people really set their home thermostats to over 19
| degrees? We set ours to 18 and often find that we're
| getting too warm
| DoingIsLearning wrote:
| A lot of commercial buildings are set above 21 celsius.
| ggm wrote:
| I don't see how it can be markedly more effective than a ducted
| propeller
| willnonya wrote:
| Even a ducted propeller has additional drag at the tips which
| this design could eliminate.
| kristiandupont wrote:
| I wonder if this design would be applicable in turbines as well?
| simne wrote:
| Most probably, no.
|
| - Turbine wheels noise is usually shielded by enclosure, and
| exists other powerful sources of noise, for example, intake.
| Yes, much noise of heli create intake air.
| ubj wrote:
| It's interesting how similar this design is to a UAV propeller
| design that was created by MIT Lincoln Laboratory [1]. Not
| claiming that anything nefarious happened--it's just interesting
| how people often unknowingly converge on the same design.
|
| (For the record, it looks like the MIT LL patent was filed in
| 2017 [2]--not sure how that compares with the patents in the
| article.)
|
| [1]: https://news.mit.edu/2022/lincoln-laboratory-inventions-
| win-...
|
| [2]: https://patents.google.com/patent/US20190135410A1/en
| Cthulhu_ wrote:
| I wonder if the company in the article decided to focus on
| marine propellers because they could secure a patent
| specifically for marine use.
| flybrand wrote:
| Quiet could be a big driver. I advised a drone co w a contract
| to inspect off shore turbines and they did testing to show how
| quiet their product was so as not to disturb marine mammals.
|
| Also, we've been eFoiling a lot and it is so calm compared to
| being on the water in an ICE propelled craft!
| andrewflnr wrote:
| I'm still curious if it reduces noise on drones, though. Can 3d
| prints stand up well enough to be used as propellers, so someone
| could test it?
| anentropic wrote:
| I wondered if this design is heavier for same lift? Might be
| part of the reason for moving development to boat propellers
| simne wrote:
| People in Ukraine print small props. But conventional design.
| For small electric engines good enough.
| snshn wrote:
| Yes, ABS is supposedly strong enough for that.
| WrtCdEvrydy wrote:
| I wonder if we'll see a 3d printable version soon.
|
| I'm thinking of putting it on the Mini 2 and seeing what
| happens.
| dhc02 wrote:
| Indeed. https://www.thingiverse.com/search?q=Sharrow&page=1
| &type=thi...
| ISL wrote:
| Probably not without violating a patent.
| moffkalast wrote:
| If you went around looking for patent and copyright
| violations on thingiverse you'd probably need to remove
| most of what they've got.
| simne wrote:
| Yes, You are absolutely right. Anybody could try any
| shape for scientific experiments, but sell copies and
| distribution of 3d models prohibited.
| hsuduebc2 wrote:
| I'm kinda sure that if he is not going to sell it they
| really don't care.
| ri0t wrote:
| Edit, to clarify: i refer here to 3D printed boat props, not
| for copters.
|
| I'm considering this as well. I have an electrical outboard
| engine on my 24". 600W is way less stressing on the material
| than even small combustion engines.
|
| I'll maybe try a 3D printed one next year. According to
| thingiverse, folks already successfully use printed props and
| the sharrow-design is there, as well, just need to adapt the
| mount and make sure the printer is up to it (i.e. convert from
| PLA to ABS, may have to get a new nozzle)
| jpgvm wrote:
| It would be really interesting to see what his attempts with
| aircraft amounted to. Propeller tip induced turbulence is a non-
| trivial portion of what makes general aviation (GA) very loud. If
| we could make the aircraft less loud without significantly
| reducing their performance perhaps GA would be more amenable
| (along with other changes like moving eventually to electric
| power plants). As it stands right now the general public isn't
| much of a fan of GA and there is always strong push-back to
| creation of GA airfields which I think is a shame. The joy of
| flying shouldn't be limited to commercial pilots and yet
| increasingly here in Australia that is the way it is.
|
| Things are very different in the US because their GA culture is
| older, more powerful and protected by the FAA and pilots
| associations.
| jillesvangurp wrote:
| I'm guessing the stresses on the propellers at high rpms
| typical for planes might be an issue. The issue with plane
| noise is the tip of the propeller breaking the speed of sound.
| This is what generates a lot of the noise. Having a lot of mass
| there might be an issue. The prop might rip itself apart. Rpms
| in water are a lot lower so, it's less of an issue there.
| punnerud wrote:
| If you change the angle of the blade, you can have lower rpm.
| This increased push is a drawback on a normal propeller
| because more air it pushed outward (loss). This design could
| solve both of the problems.
|
| So airplane propellers can have more push and lower rpm.
|
| Some years since I last designed propellers and did run CFD-
| analysis on them. Could be fun to try it again. This was my
| last attempt:
| https://no.m.wikipedia.org/wiki/Sivilingenior#Utdanning
| [deleted]
| ericpauley wrote:
| Another factor is that lots of small GA airplanes are direct
| drive, and so need to run at high RPM at takeoff to produce
| full climb power. Geared powerplants like Rotax can reduce the
| overall tip speed here, and constant speed props can help to
| some extent. Turbine props need to be geared and tend to run
| lower tip speeds, so small GA is actually having an outsized
| negative impact here.
| paulmd wrote:
| Overall I don't think the FAA or insurers are keen on
| increasing the number of high-performance GA aircraft out
| there. The step licensing between ultralight - light sport -
| GA - complex aircraft really is designed around "the less
| power, the less likely you are to get yourself into trouble".
|
| The overall wisdom of this is a little questionable and crass
| of course, since there are also accidents that perhaps could
| have been recovered with more power.
| bombcar wrote:
| GA to complex (and high-performance, they're technically
| separate) is actually a pretty small leap; you just need a
| flight instructor to sign off that you've done the needful;
| there's no actual FAA exam. It's hard to find a high
| performance that isn't complex and vice versa, of course.
|
| Moving to a twin is a separate exam.
|
| A big part of all those is the price of running the bigger
| plane/larger engine.
|
| You could have a plane with constant-speed prop and fixed
| landing gear and it wouldn't be complex (unless it was a
| seaplane).
| azalemeth wrote:
| At least in (my experience of) Europe, the main objection
| to more powerful engines is the proportionate increase in
| running costs. The trend lighter, more fuel efficient GA
| has been entirely driven by cost-per-hour, and longer term
| maintenance costs.
|
| I used to do a lot of gliding and the most powerful
| aircraft routinely flown was a Piper Pawnee (175 kW / 235
| hp engine, in contrast to say c. 120 kW / 160 hp for a
| Cessna 172), used as a glider aerotow - and even then most
| of the time we had [electric] winch launches. The pawnee
| once memorably broke a cylinder head while on tow out and
| had a sufficient power reserve to both get the glider to a
| safe altitude and fly the rest of the circuit without
| issue. At the rest of the field, all of the GA aircraft
| were highly fuel optimised and mostly run by "normal
| people" worried about the cost per hour more than anything
| else. Even the aerobatic aircraft - CAP 10s - had less
| powerful engines than that Pawnee. I didn't see a super- or
| turbocharger, and the only people flying twins at nearby
| airfields were entirely doing it for the point of
| [commercial] pilot training.
| p_l wrote:
| I remember dealing with aerotow, and there was definitely
| a feeling that Yak-12 that we had (with 260hp) was much
| better towing than 100-odd hp Morane Rallye.
| jacquesm wrote:
| Slower props are usually larger diameter though aren't they?
| That to a large extent would offset the tipspeed gains by
| using a lower RPM. Or do they run slower props at a steeper
| root angle (more 'bite')?
| ericpauley wrote:
| Great question! Turboprops spin way slower so even though
| they're larger the resulting tip speed is slower.
|
| E.g., turbo prop (source https://www.quora.com/How-fast-is-
| the-tip-of-a-turboprop-bla...)
|
| I double checked this math and got 474mph.
|
| Meanwhile a Piper Arrow (4-seater piston, pretty comparable
| numbers to most Lycoming/Continental singles) takes off at
| 2700 rpm and has a 74" propeller, for a tip speed of
| 594mph. You can use a 3-blade propeller to reduce the
| diameter and cut noise somewhat (among other benefits).
|
| Both of these are just the tip speed relative to the plane,
| I suppose you'd need to factor the airspeed too and use
| Pythagorean theorem but I'm no aerospace engineer.
|
| As you noted, this is possible because the constant-speed
| prop on the turboprop allows it to take larger bites of
| air.
|
| The Arrow needs that rpm to produce full takeoff power.
| However after takeoff it can be adjusted to a lower speed
| with minimal loss in power (e.g., 2500 rpm greatly reduces
| noise while losing 7-8% power). To reduce RPM like that in
| a fixed pitch you'd also need to reduce manifold pressure,
| causing more power loss.
| edrxty wrote:
| The Arrow also has a constant speed prop, the difference
| is the Arrow is direct drive from a massive 360 cubic
| inch engine whereas the turboprop has a gear box. It
| needs this displacement to produce power while at such a
| low speed for the prop. At almost 6 liters, yet producing
| only 200hp, it's wildly fuel inefficient, and it's fairly
| trivial to produce this much power with a modern ~2L
| engine. This is almost entirely due to a single bad
| engine design that had resonance issues from several
| decades ago so the industry (stupidly) considers anything
| but direct drive to be taboo. This is changing slowly
| with some newer light sport engines that have gearboxes,
| however.
|
| If it had even a modest reduction drive, you could run
| the engine at a reasonable power setting while
| maintaining a more efficient tip speed but the prop and
| engine engineers had to meet in the middle resulting in a
| highly compromised solution.
| ericpauley wrote:
| The IO-360 is actually a fairly efficient engine when run
| properly. Similar to Ford's ecoboost line per
| https://en.m.wikipedia.org/wiki/Brake-
| specific_fuel_consumpt... (The -720 is basically
| equivalent design to a -360 just doubled). Airplanes use
| a lot of fuel because air resistance varies with v^2, not
| because of poor engine design.
|
| Sure there have been improvements in modern engines, but
| these primarily target efficiency across power outputs
| whereas (as sibling noted) planes tend to have stable
| power requirements.
|
| Not sure what your point is about constant speed or
| gearing because I already said that.
| jabl wrote:
| > At almost 6 liters, yet producing only 200hp, it's
| wildly fuel inefficient
|
| Is it? I've always thought that while GA engines are in
| many ways stuck in the 1940'ies, they are actually quite
| efficient. Wikipedia seems to back that up at
| https://en.wikipedia.org/wiki/Brake-
| specific_fuel_consumptio... , with a couple of Lycoming
| engines producing BSFC numbers in the same ballpark as a
| modern car engine or Rotax.
| ericpauley wrote:
| Exactly this. Lycoming engineers weren't stupid, and
| airplane engines are well-designed within the (admittedly
| potentially contrived) direct drive constraint.
| FL410 wrote:
| Yeah, the thing people always miss is that these engines
| are flat-rated at whatever hp. I.e., they'll do it for
| most of their operating lives, vs. the occasional WOT in
| a car.
| tyingq wrote:
| Right...it's 200 BHP @ 2700 RPM, which is way below the
| RPM range you would measure peak horsepower in a car.
|
| Edit: A dyno graph from an late 1990's Corvette C5 engine
| (5.7L) shows about 170HP @ 2700 RPM. That's at the
| wheels, so probably close-ish to 195HP at the crank:
| https://cimg5.ibsrv.net/gimg/www.corvetteforum.com-
| vbulletin...
| Iwan-Zotow wrote:
| Hello, Tu-95
| p_l wrote:
| Part of the issue is that a lot of propellers in GA are, well,
| simple.
|
| We do have better designs available, but very fast you end up
| with either very complex manufacture (and thus price) for
| special aeroelastic propeller, somewhat less expensive
| automatically adjustable props, better engines (hello
| recertification! the big cost killer and what made G100UL so
| important). I do not know if scimitar prop blades require
| adjustable mechanism, but wouldn't surprise me. And then
| there's how to fit scimitar blade on some airplanes.
|
| So unfortunately non-trivial even when everyone involved is all
| for change, because change costs a lot.
| airtonix wrote:
| DrBazza wrote:
| The Thunderscreech had a supersonic propeller.
|
| https://en.m.wikipedia.org/wiki/Republic_XF-84H_Thunderscree...
|
| Unsurprisingly it was noisy.
| cameldrv wrote:
| In Europe where noise is a bigger issue you often see four
| blade props on small single engine planes. That, combined with
| mufflers make a huge difference in overall noise. It costs on
| the order of 3% of performance.
| est wrote:
| > In Europe where noise is a bigger issue
|
| I think the noise is also an important issue for CPU cooling
| fans or electric fans for homes.
|
| Would love to see such propeller made into everyday small
| fans.
| blagie wrote:
| I don't think this design would help with a CPU cooling
| fan. There's a reason they went from planes to water, and I
| think that same reason would apply even more so for a CPU
| fan.
|
| If you're going to spend the space, simply use a bigger fan
| at lower RPMs.
|
| Electric fans for homes are a more interesting question. I
| was going to suggest that a Vorando or Dyson already has a
| lot of elements of this, and gives more bang for the buck,
| but I think the two could be combined. A Vornado-style fan
| really reduces vortex shedding, but probably has some
| turbulence internally. A modified prop design could reduce
| that a lot.
| ruuda wrote:
| I'd love to see this tested at the Fan Showdown [1], it's a
| youtuber who 3d-prints user-submitted fan designs. Or given
| that the article is from 2020, maybe it was tested already.
|
| [1]: https://youtube.com/@MajorHardware
| Galaxeblaffer wrote:
| amazing YouTube rabbithole.
| dotancohen wrote:
| This tech requires a significantly wider propeller assembly
| - quite the opposite direction that consumer tech is going
| in for all but the most powerful machines. I suppose that
| gamers might accept a significantly larger case for quieter
| cooling, but for general purpose computing I think that
| larger, fanless heatsinks and smaller, more efficient CPUs
| are the answer.
| dghughes wrote:
| I'm not in a European country I'm curious do you know if
| small aircraft are allowed to use leaded avgas 100LL?
| alistairSH wrote:
| 100LL is still allowed, but like the US, there are on-going
| discussions about bans.
| punnerud wrote:
| This propeller push the water/air inward again, so I guess it
| would most logical to place it in the back of an airplane?
|
| Or move it to the back of the wing.
| kemitchell wrote:
| Reduced cavitation? Submarines?
| lyind wrote:
| This! It's one of the most important properties of submarine
| propulsion (life or death).
| ri0t wrote:
| Sailor in me doesn't give a shite, i just want more battery
| life out of the smol-angry-pixie-harbour-pusher.
| simne wrote:
| Unfortunately, not fair comparison "Although we have every
| confidence in boattest.com's findings, they were only performed
| on one boat, and unlike Motor Boat & Yachting's sea trials, its
| tests are paid for by the manufacturer".
|
| Need big scientific research, with many other participants.
|
| For example, it is wide known, that 6-blade prop give near same
| power as 3-blade but at half rpm, so tip speed is also half.
|
| Curious people, could google quiet helicopter, there are few open
| publications. Overall, same conclusions - more blades, lower rpm,
| quiet tip techniques, and try to avoid turbulence from one blade
| by other blade.
| ChrisMarshallNY wrote:
| That was two years ago. I'm wondering what's happened, since...
| brk wrote:
| For the most part, very little. They have recently entered into
| an agreement with Yamaha outboards[1] to have Yamaha
| manufacture Sharrow propellers.
|
| So far though there has not been much in terms of real-world
| validation of the props on common boats. In some cases there
| are modest gains seen (<10%), but that is not enough to offset
| the increased upfront price of the Sharrow. If they could get
| the manufacturing cost down to that of a typical high
| performance propeller it might have more demand in the market.
|
| [1]https://boattest.com/article/yamaha-cast-and-sell-sharrow-
| pr...
| bobm wrote:
| https://www.sharrowmarine.com
|
| They still seem to be around. Not rocking the world yet but I'm
| surprised that they haven't come out with a cheaper model.
| Might be harder to cast than expected.
| ri0t wrote:
| Welp, as someone else here pointed out, just print it, then:
| https://www.thingiverse.com/search?q=Sharrow
|
| Which is what i'm going to try next year - for my smol
| electrical harbour pusher.
|
| If you have one of these fancy inconel printers that spacex
| uses, you could even print a steel version. And quite big
| ones, too.
| chrisdalke wrote:
| Anecdotally (I'm familiar with the marine industry) they seem
| to be gaining popularity with the luxury center-console market,
| half as a fuel-saving metric but mostly because they're a
| talking point at the marina.
|
| In recreational marine these types of products tend to spread
| based on word-of-mouth and sell fairly low quantities but at
| higher price points. Related: Seakeeper
| (https://www.seakeeper.com/), a fairly crazy gyroscopic
| stabilization system, wildly popular but fairly quiet in the
| tech world.
| alex_duf wrote:
| Would you have knowledge of how well that would scale on a
| cargo ship and what sort of savings we could see there?
| chrisdalke wrote:
| Unsure if this would scale up but as others have mentioned
| for large ships the operation is very sensitive to cost.
| Fuel efficiency is weighed against current fuel cost, cost
| to design a technology into a new ship or retrofit,
| maintenance, etc. That said, since fuel rates are high and
| emissions regulation is set to come into effect soon [1]
| you'll likely see waves of shipbuilders adopt fuel-saving
| technology.
|
| A few problems that might show up with this type of
| prop/"screw" on a large ship:
|
| - Ship propulsion uses a fairly large-diameter prop and
| runs at very low RPM (~100rpm vs 1000-6000rpm) compared to
| smaller planing vessels. The Sharrow prop advertises
| decreased cavitation at high speeds but this effect may be
| diminished at low RPM.
|
| That said, cavitation is a different beast for ships than
| for recreational boats: In the recreational market few boat
| owners are concerned about propeller efficiency loss due to
| cavitation -- Concern is mostly around noise and vibration.
| In contrast, ships are very concerned with fuel and
| maintenance cost, so if the Sharrow blade successfully
| reduces both of these it may be helpful.
|
| - Seems like they're currently machining these on a 5-axis
| CNC out of blocks of raw material which won't scale to
| larger sizes. The complicated shape may not lend itself as
| well to casting, and even if they casted the shape it would
| need to be finished and this would require expensive
| equipment.
|
| - Might be more difficult for third-party repair [2] which
| is done manually or with 3-axis machines.
|
| Generally the commercial maritime market is much slower to
| adopt new technology than recreational, and also much
| smaller by volume, so it may make sense for Sharrow to
| continue serving small outboard boats because margins +
| sale volume is much higher.
|
| [1]: Incoming maritime emissions regulations:
| https://hbr.org/2022/10/climate-regulations-are-about-to-
| dis... [2]: Example of ship propeller repair:
| https://www.youtube.com/watch?v=RuV3AsKTQlM
| lyind wrote:
| Why isn't this shape used on submarines already?
| VLM wrote:
| On a small ski boat when something like weeds tangles or fouls
| the prop just pull the lever and tilt the engine out of the
| water and untangle by hand, including turning the engine on and
| off its likely a five minute job. Much harder with a submarine
| in the middle of the ocean.
| simne wrote:
| We don't really know, what used on military submarines, because
| real photos of their props are top secret.
|
| On civ subs, as I know, main driver of choose is just cost, so
| usually they use conventional cheap designs.
| robbomacrae wrote:
| Can the same design be used for a small windmill? Will it show
| similar efficiency gains?
| HybridCurve wrote:
| Loopwing turbines have been around for over a decade.
| ri0t wrote:
| Here, have some pics, if you wondered, too: https://duckduckg
| o.com/?q=loopwing+windmill&iax=images&ia=im...
|
| ("Aaaah, those ones! Yeah, sure!")
| willnonya wrote:
| I would suspect not given the differences in how they operate.
| I think nit would have additional disadvantages on large
| turbines where the cost and weight would increase
| significantly.
| kellyharsh wrote:
| MerelyMortal wrote:
| F...
|
| I remember sitting in a class one day and hearing that there
| would always be wingtip vortices on planes, and wondered if that
| could be solved by looping the wing around (to where it almost
| looks like a biplane).
|
| I wonder how many other ideas are being sat on because people
| don't realize its significance or have the resources (such as
| time or desire).
| mannykannot wrote:
| This issue is an unending source of discussion. The thing is,
| you cannot eliminate wingtip or wake vortices by putting a
| finite barrier at the wing tip, no matter how large. This is
| because [begin hand-waving approximation] for a wing to produce
| lift, it is necessary for the airflow passing in close
| proximity to the wing to be deflected downwards (no
| acceleration, no force.) This unavoidably creates a region of
| shear at the boundary between this wake and the surrounding air
| mass, leading it to 'roll up' into two counter-rotating
| vortices (as this is a hand-waving approximation, I won't
| mention the circulation around the transverse axis of the
| wing...)
|
| We can't banish them, but you can do things to reduce them, the
| simplest of which is to move the tips further apart (i.e.
| lengthen the wings.) Everything about airplane design is a
| compromise, however.
| sandworm101 wrote:
| There are still tips and vorticies, just not at these
| speed/size/power settings. The length of the blade is the
| biggest issue. These are effectively short blunted tips with a
| hole in the blade. Whether the improvements would translate to
| air, with all the associated speed of sound issues, is unclear.
|
| Another old option for eliminating such issues is to put the
| prop in a case, like a jet ski or most modern military
| submarines. Or just eliminate the concept of tips and turn the
| entire case.
|
| https://en.wikipedia.org/wiki/Rim-driven_thruster
| mint2 wrote:
| Wow These look like fish dicers. Not to say that propellers
| don't already dice fish, these just look the part too.
| rtkwe wrote:
| For small fish they're probably about the same but they
| seem like they'd be superior for larger fish since they
| wouldn't be able to get drawn into the middle so you'd have
| less strikes along the backs like you often see on whales
| or large sea animals.
| guelo wrote:
| Good ideas are a dime a dozen. What's rare and precious is the
| very hard work of birthing an idea into existence with good
| execution. Unfortunately, even with a good idea, hard work, and
| excellent execution, innovation still usually ends in failure.
| edrxty wrote:
| Yeah, I can say with some certainty that every aerospace
| engineer has this idea at some point then moves on to other
| things. A select few have pursued it but at least at aircraft
| scale it results in a number of other engineering challenges
| related to structures and resonance so it's usually
| abandoned. The brilliance here is applying it to an area
| where the aspect ratios are so low that the mechanical issues
| don't apply and you can just cast it out of a big chunk of
| solid metal.
| ge96 wrote:
| Boxed or closed-wing
| MerelyMortal wrote:
| Ah, thank you!
|
| https://en.wikipedia.org/wiki/Closed_wing
| mikelabatt wrote:
| A century ago engineer Luigi Stipa did experiments with several
| flying wing aircraft designs. Here is Stipa-Caproni's "intubed
| propeller" from the 1930s:
|
| https://en.wikipedia.org/wiki/Stipa-Caproni
|
| Even newer patents should cite this research:
|
| https://en.wikipedia.org/wiki/Luigi_Stipa
| [deleted]
| jacquesm wrote:
| This has already been done, for instance:
| https://www.reddit.com/r/WeirdWings/comments/6wch9q/narushev...
| pjerem wrote:
| Ok so there is an entire subreddit dedicated to weird wings.
| I'm not surprised anymore but I'm still amazed at how online
| communities can be so specific.
| pge wrote:
| Thirty years ago, I worked for the Navy and had some exposure to
| propeller design for submarines. Military propellers at that time
| were already employing complex shapes for efficiency (and noise
| reduction). While it certainly takes time for military
| technologies (especially classified ones, which propeller shapes
| were) to propagate into the civilian world, in this case, I think
| the issue is primarily cost. Civilian props have remained quite
| simple because the cost of manufacturing complex shapes is high
| (often requiring multi-axis milling machines). In addition,
| repairability and other concerns may be more important than
| efficiency.
|
| While I don't work in fluid dynamics anymore, it's cool to see
| people explore some of these ideas in the civilian world.
| Unfortunately, they may be solving the wrong problem for the vast
| majority of their users, for whom the cost doesn't justify any
| performance benefit.
| rexreed wrote:
| When I saw the word "cavitation", submarines was the first
| thing I thought about. Blame the Hunt for Red October for that
| word association. You'd think that this approach to propeller
| design would be adopted due to quieter running, but sounds like
| not.
| pge wrote:
| Cavitation isn't just a noise problem; it also causes damage
| to the blades. The forces on the blade are surprisingly
| strong. When a propeller has been experiencing cavitation,
| you can see the pitting on it, almost like you hit it with a
| pointy hammer. If it continues, cavitation can seriously
| weaken the blades.
| ri0t wrote:
| I'd wager to say that on most civilian vessels, the engine
| noise is far louder than what the prop could generate. I'm
| happily using a 600W outboard electrical - while it would be
| different than with a combustion engine, i don't think it can
| get much quieter even with better prop-design. It's a
| blessing! Almost like sailing the boat, i.e. not much louder
| than a gust of wind.
|
| Energy efficience on the other hand.. It is driven by a
| fairly average car battery, so every little Watt saved helps
| keep the drinks cooled.
| FPGAhacker wrote:
| 600W? Is that a typo? That's less than 1HP.
| fwipsy wrote:
| I don't know anything about boats, but some boats can be
| rowed by a single person, which I guess would typically
| be much less than 600w. It fits with the car battery part
| too.
| simne wrote:
| Most people are capable to do about 500-800W for long
| time (30 minutes or more), and up to few kilowatts for
| short time, 1-3 minutes.
| andreareina wrote:
| Source? In cycling those numbers are elite level if not
| beyond. Numbers for rowing are hard to come by but
| lower[1], probably drag lowering efficiency (bicycle
| drivetrains are 90+% efficient).
|
| To put it into perspective, 250Wh translates to 800~900
| calories burned in a half hour[2]. That's not something
| most people around me can do.
|
| [1] https://rowinglevel.com/rowing-times/10000m-times
|
| 250Wh = 900kJ = 215 kcal at 100% efficiency; humans are
| ~25% efficient at turning food into mechanical work so
| ~860 with error bars
| robocat wrote:
| Yeah, they are wrong. During a bicycle
| race, an elite cyclist can produce close to 400 watts of
| mechanical power over an hour and in short bursts over
| double that--1000 to 1100 watts; modern racing bicycles
| have greater than 95% mechanical efficiency. An adult of
| good fitness is more likely to average between 50 and 150
| watts for an hour of vigorous exercise.[clarification
| needed] Over an 8-hour work shift, an average, healthy,
| well-fed and motivated manual laborer may sustain an
| output of around 75 watts of power.
|
| - https://en.m.wikipedia.org/wiki/Human_power
|
| Also see "How Much Electricity Can a Human Generate?"
| https://www.pedalpc.com/blog/how-much-electricity-can-
| human-....
| simne wrote:
| Kilowatt is ~ 1.3 hp, so 600W = 0.8HP.
|
| But, here important, that electric engines have much
| better torque on low rpm, even exist electric engines
| which give high torque just from zero. Also it is
| typical, to overdrive electric engines for short time.
|
| And other important thing, aging - electric engines could
| nearly not have aging at all, but gas engines have
| significant drop of power/torque at hundreds of hours of
| work, even if properly serviced.
|
| Overall, You will really not see gas engine claimed
| power, but something much less, ~ 70-90% in good cases.
| But in case of electric engine, it will not only give
| claimed power, but could make up to 100% boost for
| limited time.
| AlexandrB wrote:
| I don't know much about marine motors but, unlike for
| ground vehicles, I don't think that having a ton of
| starting torque helps in a marine environment. The torque
| required probably increases as the propeller speed
| increases which matches traditional ICE engines much
| better than DC motors.
| simne wrote:
| UNLIKE for ground vehicles, marine and air.
|
| - From tutorial for auto engineers: "more than 90% of
| time, auto engine working at fast switching conditions,
| and extremely low load, near zero", vs marine (and air),
| where prop does near linear load-rpm function at working
| diapason.
| simne wrote:
| BTW, because autos special requirements, there widely
| used turbo-compressors, but they are rarely used in
| marine motors and not too distributed in air.
|
| This is because, turbine only eat power and does not give
| anything at low rpms, only effective on medium-high
| diapason.
|
| For planes, turbine only gives an increase at
| significantly high altitudes, so, for example, typical
| light plane does not got improvement if flight on typical
| 1000-2000m, but got if go much higher, 5000m and more.
| kortex wrote:
| What is "diapason"? I looked it up and the closest
| definition was "a burst of sound", the rest pertained to
| pipe organs.
| bmelton wrote:
| Probably not. Even large, 40'+ boats designed to operate
| primarily by sail can get by with 10-20HP. Motorsailers
| -- racing sailboats designed to go faster by leveraging
| both the wind and a motor -- typically aren't much more
| than 40HP.
|
| What's interesting about this prop (to me, anyway) is
| that most of the sea-faring boats that need it the most
| will likely not use it because it doesn't feather or
| fold-away when not in use. For ocean-faring sailboats,
| that's critical, as the drag of trad props will cap their
| speeds by half a knot or so, which (over the span of a
| multi-week journey) might add meaningful amounts of time
| to a trip that you're just hoping to finish with.
| kibwen wrote:
| Given what we're learning about the effect of propeller noise
| on marine life, I can foresee certain countries outlawing the
| sale of noisy propellers if reduced-noise versions become
| broadly available, even if they are more expensive.
| janalsncm wrote:
| The article says he moved from drones to boats. I wonder why. I'm
| very interested in drone propellers that could be quieter.
| nokeya wrote:
| Could it be applied to PC fans? To reduce their noise
| lsaferite wrote:
| Is the fan shroud not mostly solving or mitigating the tip
| vortex issue on something like a computer fan?
| knolan wrote:
| Certainly but as I've learned the economics aren't there. In a
| previous role we developed a novel heatsink and fan design and
| saw some licensing interest. We learned that all that matters
| for thermal management solutions was cost above all else.
| Existing designs were good enough.
| moffkalast wrote:
| Idk, Noctua's clearly making bank off premium ultra quiet
| fans. At least from me.
| ri0t wrote:
| You're _way_ not alone. Love those ugly-brown quiet-
| machines. Still, they 're probably looking at this and
| think "Nah, our optimizations are way cheaper to
| manufacture and wholly sufficient" (because they are :)
| KingLancelot wrote:
| operr wrote:
| [1] Similar concept for Small Unmanned Aircraft Systems by
| Lincoln Lab
|
| [1] -
| https://www.ll.mit.edu/sites/default/files/other/doc/2022-09...
| mhb wrote:
| In the video showing the cavitation comparison, why aren't the
| central parts of the propellers more hydrodynamic? Like the
| typical pointy shape. It seems like it would make the contrast
| between the two propeller designs at the blade tips more apparent
| if the predominant source of cavitation wasn't due to the feature
| they have in common.
| Neil44 wrote:
| Fans are a big deal. Imagine if you could improve the efficienty
| of every fan in the world by 5%. Aircon units, air movers,
| cooling, yadda yadda.
| Cthulhu_ wrote:
| Not to burst your bubble, but the technology is there to do so,
| if not much higher than 5%; it's just a matter of cost at
| scale.
| VLM wrote:
| Something that disappoints me about the comments to this story is
| no mention of engineering optimization.
|
| The marketing shows it outperforms at very high power level at
| very high speed.
|
| Then the message veers off into ultra low speed modest power
| level applications like bulk cargo hauling, and fairly generic
| greenwashing, we can save the earth with this one nifty techno
| trick.
|
| A better application would seem to be unlimited-class racing boat
| props or military-industrial complex torpedo propellers. They
| have infinite money, which makes the situation interesting.
|
| There's an old joke that an engineer and an economist see a
| nickel on the ground and the economist tells the engineer not to
| bother trying to pick it up because the efficient marketplace
| theory proves there can't be nickels laying around ready to pick
| up, therefore it can't be there, must be an illusion. However, in
| the context of people with large amounts of money willing to pay
| anything for higher performance, it seems odd that a mere
| propeller shape could exist that nobody is already paying for,
| that nobody has been paying for over the last century.
|
| My theory would be there's something about this prop that nobody
| is talking about. Most boats most of the time are not full
| throttle. WRT durability I wonder what its cavitation behavior is
| like.
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