Why Are 4 Blades Better Than 3?
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- čas přidán 9. 03. 2023
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✩ABOUT THIS VIDEO✩
In this video, we investigate why the number of blades on a propeller matters and why 4 blades can be better than 3. We also touch upon why Titanic might have had a different number of blades on her propellers and what experiments they may have been running.
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2:40 Actually, the very first screw propellers WERE Archimedes screws, but it didn't take at all long for designers to realize that blades could do the same job more efficiently.
The realized when a screw broke and the ship became faster
@@jamesricker3997
Wow!! That is very interesting. Thanks for sharing.
Blades are essentially still the archimedes screw, just cut to pieces and its parts moved next to each other instead of going one after another.
@@kasuha in an air propeller, the cross section is modified into an airfoil.
Is that done for water propellers, too?
Or does it not make as much sense with an incompressible fluid?
@@nos9784 yes, the cross section of a ship's prop is also heavily engineered to produce the most efficient design/best combination of characteristics.
I heard that the Victorian engineer who "invented" the first prop had actually started with an Archimedes screw, but it broke, rather than waiting for a new casting he just continued with his steam boat the tiburnia, and the prop worked better than he thought.
Turbinia en.wikipedia.org/wiki/Turbinia
@@rogerwilco2 Turbinia is a later development, pioneering the use of steam turbines -- the Archimedes screw that broke belonged to an experimental boat built by Sir Francis Pettit Smith, which suffered the fortuitous screw damage in 1837.
The Propeller was invented by Josef Ressel, an austro-bohemian forester.
John Ericsson had stolen this invention and patentend it first to earn all the benefits for it...
an intersting situation is that the Iowa class battleships and liner SS United States all have 4 propellers, with the inner ones having five blades and the outer's having four. This combo was found to be effective when trying to reduce the shaking the North Carolina class battleships made at speed. The Iowas and SS United States were designed for speed so took that lesson and added another rudder for fast turns at speed as well. This design was classified at the time and SS United States only got to use it as she was designed to be usable as a high-speed troop carrier in case of war
ss america is excluded i guess?
Similar trials were done with 4 and 5 bladed props on the South Dakota class, but I think vibration and fuel consumption issues were never really solved due to those ships being in service for such a short time.
@@CuoreSportivo she is earlier and has twin screws- the design I mentioned is only needed on 3+ propeller ships
fun fact: the vibration issues on the North Carolina class battleships were so bad that they were limited to a 24 knot speed for some time until the issues had been solved by the propeller swapping. It was feared that higher speeds would damage some of the more sensible equipment on board (rangefinders, radar, etc.). This was obviously a HUGE issue when the cause of the vibrations was unknown (at first), the 4 South Dakota class battleships were nearing completion (with the fear they would have the same issues) and every other newly constructed battleship around the world was reaching top speeds between 28 and 31 knots without problems.
Also, subs and anything "stealthy" will have a prime number of blades. Because noises with harmonic multiples thereof are rare in the natural world, and thus a giveaway of manmade origin. Pretty niche factiod, but there it is.
Years ago, we used to listen carefully to surface ships to determine their RPM and blade number. It helps submariners determine just what sort of ships are in an area. The details of making super-quiet propellers was always a highly classified aspect of subs. Many times in photographs of subs in drydock, you'll see the propellor area blurred or covered in canvas to try to keep secret the details.
From what I've heard the prop is also covered up so you can't estimate the frequency from the image
@@Vinzmannn as a former navy soldier I can confirm this.
also submarines hav a lot of blades to reduce noise
They still cover props when launching new submarines.
That's also another reason cavitation is bad--it produces a lot of additional noise, which is undesirable for reasons of both sonar stealth and underwater noise pollution.
IIRC wasn't this a bit of a concern back in 2010 when HMS Astute ran aground off Skye, there was a chance the tide might drop far enough to leave the screw at least partially above water.
*_Props_* to Casual Navigation for bringing this to our attention. 😉
You need to *screw* your head on tighter if you think that was a good pun
I sea what you did there!
This joke had me spinning on the floor
This joke killed my grandma that spon round round round
Screw your pun.
There's also really weird propellers, like toroidal propellers, and the 7 (or more) blade swept propellers on modern subs that somehow sustain 30+ knots while also being extremely quiet and low-cavitation
Well one of the biggest factors there is that the higher pressures at depth mean that higher propeller speeds are needed for cavitation to occur.
I presume that with nuclear power efficiency is less of a concern, so you can optimise for quiet speed and don't worry so much if you're sinking a few more MW into the machinery
@@andrewbroeker9819 bollocks they got so many blades so they can turn slow while giving out the same pushing force... so 7 blades doing 88rpm will give you the same work as 3 blades doing 120+rpm
30+ knots *OR* zero cavitation. Pick one.
I've seen some open-source stuff about certain modern SSNs being able to run at 20+knots and still being considered "quiet", whatever that was intended to mean.
At 30 knots though, even those super-quiet skewback props will be whipping the water to a boil.
@@gustaveliasson5395 Don't forget that at greater depths pressure of water rises and pushes cavitation point to higher RPM and thus higher speeds
Kudos to your animation of the Titanic not having smoke come from the fourth funnel.
🤯I forgot this trivia
May be one of their gene was stopped 😁
Can you say why?? I've not heard this before.
@@Peds013 the fourth one didn't have an engine underneath, it was added by the builders because they thought the titanic would look stupid with only three. in the end they used it as a vent for the kitchen
@@dari6795 that's hilarious! Thanks for sharing.
I've heard a story from my father who manages a boat making company and his friend who makes propellers. It appears that some boat owners (especially in context to law enforcement and defence) prefer 4 bladed/even numbered props so if one of the props are damaged/cut off, they can cut the opposite side and make it a 2 bladed prop and maintain relative stability/minimal vibrations.
This is valid. I've witnessed the result of a prop strike on a large cargo vessel with a four-bladed screw. The tip of the opposite blade was cut off by underwater divers to balance the load until the next dry dock for a better assessment and more permanent solution.
If this is true I woulsd expect a 6 bladed prop. Becaus that can be changed to a four bladed one (blades not even divided in the circle) , a three blades one or even a 2 blades one if damge occur.
@@reiniernn9071 But that's not the only concern and more blades have downsides as well, so it might be that 4 is the sweet spot. 3 can't be balanced easily if damaged, 5 likewise and 6 might be too many blades for other reasons.
@@reiniernn9071 6 would be a bit overkill for small 30-40 meter boats to be fair.
I thought of military used vessels...more chance on damage what must be bypassed And much biogger like also container freighters..
Its fun to note that things like Nuclear Submarines, which desperately need to keep cavitation to a minimum, tend to have tons and tons of blades, and I believe some even have variable pitch propellers like you see in many aircraft, allowing you to even more finely optimize your blades to your immediate circumstance
Also ducted, almost approaching what you see in turbofans, in order to help contain trailing edge vortices, and I think I've also seen contrarotating ones mentioned? But inline, rather than one on each side, which also does its own thing. All very very secret tho!
@@fairguinevere666 ya submarine propellers are such a tightly guarded secret but they're called pumpjets because they have large cowlings around them
Never heared of a submarine with CPP, and I guess it is to dangerous to loos tje pitch control. That Submarines have so many blades is exactly one point he made completely wrong. To reduce cavitation you need to go down in pressure level. To do so with a given power you need for a cirten speed, you increase blade number. Which will reduce your efficency as more blads mean mor friction and resistance to turn the prop.
@@AsbestosMuffins some submarines have pumpjets, but definitely not all.
Variable pitch props are a very common application especially on medium freighters and large private motor yachts
Remind people, this also applies to aircraft propellers. The calculation numbers are VERY different, because air is a lot less thick that water, but the same factors apply.
With aircraft, 2 blades are generally favored, but in general, as horsepower increases, so do the number of blades.
The new ge9x engines has 16 blades instead of 22 which makes it more efficient than the previous gen GE90 engines.
@@jirehla-ab1671 I did say in general, and the blades are substantially larger as well.
True, although 2-blade aircraft propellers are only "preferred" (used because they are cheapest) in the smallest sizes. Cessna 152: 2-blade. Anything with a turbine engine: 3 or more blades, up to 8 blades in the largest turboprop military transports.
@@brianb-p6586 My best friend from college is an aerospace engineer, works for Lockheed Martin. Twin bladed propeller are preferred because they are most efficient. They add extra blades because 2 blades can only handle so much horsepower. As you point out, as engines get stronger adn stronger, they have to increase the number of blades. But two blades is the best at getting the most thrust from the available power.
I used to have this toy set called Capsela for building your own motorized vehicle toys, it included a propellor with 4 blades that could be adjusted so you could see the effects of high or low rake on your little boat, and which best fit your design as it paddled around the bathtub
Only real ones remember Capsela.
I remember that. Capsela was amazing!
That takes me back
Now everyone on the internet knows what you do in you bathtub.
Once again the parallels between aviation and seafaring are uncanny. Very well explained and animated, as always, Mr. C.N.
Fluid Dynamics, Density is the only major difference.
@@1978sjt yeah but the speeds are much different and water has a much higher voscosity which make these two completely different beasts. It's like comparing cycling and f1. Both have wheels but are completely different
@@robertr7923 not COMPLETELY different, that's the point, but yeah, I wouldn't want to be spinning a ships prop as fast as a planes, because... well... physics :p
@@1978sjt The biggest difference is that seafaring is about resting on top of the water whereas aviation is about flying through the air. Submarines are more like planes than boats are. If one were to sail a ship floating on the top of the atmosphere through the void of space it would be more like an air boat lol
@@jek__ oh how cool would that be!
3:30 I wanted to point out that screws are very rarely made of steel for ships. Most of the time they are some alloy of bronze. Great video!
Why is that?
@@Cyberguy42 Bronze is much more resistant to seawater. It can also be made to be VERY hard, which protects against cavitation damage. It's also very expensive - some screws for larger ships weigh over 100 tons and cost in the millions to produce. It's amazing to see these massive things that are made in a single casting.
@@doggonemess1 CA 958 aluminum nickel iron bronze, is incredibly corrosion resistant and cavitation resistant, (and pretty strong) its usually used for propellers, or some more highly refined version of it
i would love a deeper dive into propeller theory
Me too. I'd love to see it start with the theoretical physics - what works best when you don't have to think about engineering, the hull of the ship, maintenance etc - and then introduce those features to show the trade-offs.
Like Submarine Props? :p
Cutters for milling machines and similar have the same challenge; more edges on cutters has costs and benefits.
I wouldn't know how interested I am in this stuff without this channel existing. Thanks.
A single-blade propeller wobbling the ship to bits? Sounds like something the kerbals would do.
There have been Experiments with ingle bladed Wind Turbines and Airplane Propellers, both with Counterweights. Neither was very successful.
Now I want someone to develop a KSP prequel, where the goal is to build a ship that can circumnavigate the planet.
@@danielbishop1863 kerbal ship program
@@danielbishop1863the guy who made the original is developing a new game and I think their are boats in it
I have officially watched all of Casual Navigation’s videos. The quality of information has always been top notch and the visual aids keep getting better and better!
I'm pretty sure the mystery of Titanic's central propeller has been solved by the discovery of the order for a central 3-bladed propeller a couple years back
I appreciate your attention to detail, the animation shows smoke emitted from only the front 3 funnels, which is accurate indeed.
why is that?
these videos have a rediculous level of quality. Soo good. Technical depth and animations everything is on point. Big fan!
I really look forward to your videos & smile when I see a new one has posted 🤗 They are always very well done & properly explained. The animation you use is easy to watch & always extremely helpful in explaining your point. Thank you for doing these 🙏🏻
I like that the animation at 0:40 shows smoke coming only from the first 3 chimneys. Nice attention to detail.
In the thumbnail, in actuality, the three blade prop would have huge cloverleaf blades, and be slightly larger in diameter. More bite at lower speeds. The 4-blade would be a smaller diameter with less surface area per blade, more rake angle, and one extra blade. More speed without requiring more engine torque. I run both types on my cabin cruiser depending on my load and requirements for that trip. Lower rpm from a slower speed yet more efficient 3 blade may take a bit longer to get there, but you save a hell of a lot in fuel costs when you need 300 gallons to fuel up.
I have absolutely enjoyed this quick introduction to the topic. 👍👍
Oceanliner Design channel also pointed out about this ptopeller fact in one of his Titanic videos. The idea was Titanic was going to test out the three blade design, but it sank, so Olympic propellers were switched to test the tree bladed propeller design.
Oceanliner is the source of this video. It came out earlier.
i really like the way you explan things with graph... this truly is the engineering's approach when it comes to making stuff and testing it
Excellent video and presentation. 24 years ago I bought a 27 ' long ex ships lifeboat with a steel hull. It didn't have the propeller though. I stripped it of all it's wooden structure and rebuilt it in steel to live aboard. I got a Lister engine for canal work. I went to the library and got books about propeller design for boats. Hmmm...........I'm a life long electrical engineer........
I finished the design and sent it to a manufacturer in the Midlands and they sent me back my shiny new propeller !
THEN in a twist of fate, the original propeller turned up ! ( a long story ! ) My new propeller was almost identical. Same diameter, same pitch, just 5mm different blade diameter !
And it worked fine . Thanks again, Colin ( West Yorks )
Another question::Why not 100?
A four blade prop has less rake than 3 blade prop .
Rake = how much you push the water for each revolution of each blade .
A 8 blade prop would have even less rake for each blade compared to 4 blade prop .
So a 100 blade prop would just be so inefficient. It not worth it for ship prop .
According to 1935 principles of warship construction and damage control, 'Three-bladed propellers are usually preferred, because they are more efficient than four-bladed propellers, unless diameter limitation makes the four-bladed propeller necessary. Propellers with more than four bladdes are practically never used.' It's interesting to see how as our understanding progresses we are actually able to take advantage of configurations previously 'practically never used.'
More than 4 blades are generally used on submarines - 7 to 9 blades. Key reason is to reduce cavation noise and efficiency is secondary to evading detection. Uneven numbers of blades avoid resonance effects.
@@voster77hhIs this true for non-nuclear subs (Diesel or AIP) as well? (I'd imagine that they have more incentive to care about efficiency.)
@@halfsourlizard9319 detection goes before efficiency. All sub drive trains go by electric anyways to avoid complex gearboxes failures and mechanical noise and vibrations.
High level prop cavitation acoustics is the most relevant noise after sonar pings from the rubber coated hull signature. Also the prop cavitation is an active noise emitter detectable by passive sensor arrays.
It does not make much difference doing diesel-electric, nuclear-steam turbine-electric or fuel cell electric.
Nuclear has a lot of cooling gear pumps noise, diesel a lot of mechanical. Silent Hydrazine FCs is 1950ies miltech.
Without a low cavitation 7 to 11 blade pro design subs are super easy tompassively detect, no matter the power source. Best FC only or diesel-FC hybrid subs frequently pop up in US carrier groups in NATO exercises.
it has become kind of a sport to sell them as a product. Anyone can do a few cell or nuclear reactor but few can do a low caviation prop.
14 y/o did go Sheldon Cooper an built a fusion reactor in a NYC apartment home. Low cavitation prop design is way more challenging single feature engineering.
I'm a 38 year old home health aide. My only experience with shipping is at The UPS Store. 😆 I have no real interest in boats and live in a land locked state. Why am I so fascinated by your videos? I've been a long time subscriber! Thanks for entertaining my curios mind.
bigger is always better.
always.
Titanic: ...
The compromise between blade angle, power and speed is of course something that variable pitch props can change on the go depending on operating conditions and required performance. Those are widely used in aviation, but apparently not nearly as much in the naval world.
Variable pitch props are widely used in marine applications that require a range of operating speeds. Ships that are designed for very efficient, single speed operation like container, bulk or tanker designs will be optimal for their cruise speed which is maintained for >95% of the voyage. Losses during the 5%, usually slow speed, portion of the voyage just aren't worth the cost and complexity. Ships like underway replenishment ships that spend time loitering at 5kts, replenishing around 15kts and transiting at 20kts all have variable speed probs.
As a Pilot, I love watching these videos! The similarities between aircraft and ships is always astounding! Whether its terminology, navigation or even propellor theory!
This is a beautiful elegant explanation of propellors.
60 tiny blades is the best.
you should do a video on Voith Schneider Propellers, they are very strange.
A couple of weirdness items regarding propellers. 1) paddle wheels - they had advanced, high-efficiency paddle wheels by the time they went out of fashion, on which the paddles could be tilted fore-and-aft; they thusly entered the water more closely vertical and remained so throughout their paddle-motion; the drawbacks being increased complexity, higher maintenance and more susceptibility to breaking. Interestingly, reading about human-powered boats, the second-last record-holder (that I read about) was paddle wheeled - it was beaten by a propeller driven boat made by MIT, but the propeller was very large and light, and turned in the air, not the water. And 2), your mention of an Archimedes screw is very apt. One of the early propeller experiments was run on an English river, with a propeller that was indeed an Archimedes screw - it worked, but the screw was flimsy and ultimately tore most of itself off the end of the propeller shaft - and the researchers were considerably nonplussed to discover that, having lost most of their Archimedes screw propeller, the fragment that was left on the shaft propelled the boat significantly faster! Life is funny that way... 3) Big ships' propellers are almost never made of steel; steel rusts. Usually they're made of marine bronze, a semi-precious metal ("precious" because it costs so much...).
Love the attention to detail in this video. Right down to the titanic not emitting smoke from the fourth smokestack as it wasn't actually connected.
you can hear this same cavitation effect if you've ever overrun a pump. it sounds like hammers rapping on the case. i.e., if you have tried to pump a fluid with a clogged filter or strainer, or through a small hose. the telltale signs are increased pressure with no increase in flow
You have Cavitation wherever a Liuid flows. It also is a huge Challenge in Hydro Turbines, and badly designed Plumbing can cavitate as well. A badly designed Ship Rudder can be "consumed" by Cavitation Damage too.
@@Genius_at_Work you're right, i think the proper term is supercavitation. gets to the point where the collapsing causes damage. at least how i remember it from the school books
@@loginavoidence12 Cavitation always causes Damage. IIRC, Supercavitation means creating a huge Vapour Bubble around a Torpedo to reduce Drag, thus allowing it to reach impressive Speeds.
I find it interesting that most submarines have 7-blade propellers both conventional or nuclear-powered although the more recent classes of SSN or SSBN have a pump-jet instead of a propeller blade. I wonder if someday will see Pump-jet Propulsion be introduced to conventional submarines?
Not too likely but not impossible, the main issue comes with the power needed to drive those pump jets which a nuclear sub can easily provide while conventional subs dont have the same massive power on tap
The thing to keep in mind with submarine propulsion is that they are more concerned with noise reduction than efficiency, so they might use a design that is inefficient but quiet, not suitable for a surface ship, much less anything civilian. I could see pump-jets being used on conventional subs though, again a question of efficiency versus quietness. A compromise (both mechanically and in terms of performance-versus-noise) would be a ducted propeller.
The replacement for the Australian Collins class was supposed to be a Diesel Electric pump jet submarine but got cancelled when Australia changed its mind and went nuclear for the next generation.
Current word is Australia will lease a half dozen Virginia class submarines prior to building a variant of the Astute class submarines for themselves.
@@quillmaurer6563 See "Kort nozzle"
There are many issues with pump jets when the focus is to operate quiet.. One example is the noise the nosle makes in addition to the impeller and volute. The reason submarines has seven blades is that 7 is a prime number, i.e reduce the potential for harmonics.. As others have pointed out a 5 blade propeller has cavitation issues and 11 blades would be too inefficient, so 7 it is!
4:09 That explains why submarines have propellers with many blades. Each additional blade reduces the noise!
As usual, concise and informative without getting too far in the weeds. Small note, sailing vessels with auxiliary propulsion, also have the option for folding or feathering props that have less drag than a small inefficient two bladed prop while sailing and more blade area and or blades under power. This comes at a cost of more cost and maintenance.
4 blades help give more speed when leaving
Thank you for the explanation. Can you make a video about toroidal propellers?
And pump jets
uai*
Before playing the video it would have never occurred to me that you could make such a subject so fascinating.
I absolutely love the example showing how the vortex generation and wasted energy would be done to the extreme! It made is so easy and immediate to understand why what works right does work right.
I wish more educational content would do bracketing in their examples (showing the unrealistic extremes, for reference to effects), because it's absolutely the fastest way to determine so many scenarios. I try to use this methodology in my experimentation with absolutely everything because of how effective it is (I never change small values first).
This has earned you a subscriber!! =)
Would be nice to see also the toroidal propeller im comparison
Steel? Bronze more common…
Cool video! I experimented with two and three bladed propellers on my last sailboat. The two bladed propeller was more efficient motoring in flat water, but vibrated a bit more, and was less effective motoring straight into choppy seas than three blades. The two bladed propeller folded better for greater efficiency when sailing, so as you said, everything is a compromise!
Thank you for teaching me this information I never needed to know.
You focused on Titanic. This ship (I suppose many others) had different type of engines. The outer ones were piston engines while the middle was a steam turbine. So for me there must have been two solutions since the different machines might have different operating speeds.
With the development of linear induction motors, is it possible that a full sized Archimedes screw in something like a tunnel through the hull could ever become a thing?
What you're describing sounds a bit like a rim-driven thruster, which has blades projecting inward from an outer ring and no central hub, the ring acting as an electric motor. They still use multiple blades though, the full archemedes screw wouldn't be very efficient as a propeller - would tend to spin the water rather than move it.
en.wikipedia.org/wiki/Rim-driven_thruster
well the closest thing to that would be a jet boat with an impeller, and i doubt extending the length would help.
Propeller i en tunnel användes på gruntgående mindre ångfartyg som som skulle gå i grunda strömmande vatten, fanns en sån i indalslälven i Sverige på tidigt 1900 tal
Amazing video - what a wonderful explanation presented so succintly!
That was very interesting mate I built a model boat and was struggling to get the propeller right I think this has given me the right idea thanks buddy
20 seconds ago
Yo what emoji is that
Really cool vid. Thanks for uploading!
Love this channel it's just
"Wanna know something random"
And it just fits on youtube
Great video, thank you.
I saw some software simulations linking the number of blades of the propeller with the frequencies of the harmonics generated while it is spinning along all the speed range, and how the propeller is designed so to avoid these harmonics are far from the resonant frequency of the ship itself. In this way, the designer avoid that - within the constraints of efficiency and cavitation - the vibrations of the ship are kept at the lower possible level.
Thanks once more,
Anthony
Exactly the level of explanation that I needed!
Great video and well explained!
I find Sharrow Propellers quit interesting yet no one has ever used them on a large ship despite all heir promises which they already proofed on smaller boats.
they haven't yet been tested independently , waiting for that
@@licencetoswill actually they have been tested on boats independently and they are the real deal.
I love you describing your film as an introduction, where I would call it a synthesis 😉 Delivering substantial knowledge i such a short time requires a mastery level of understanding. Nevertheless,I am sure, it took you not a short time to prepare it Thank you for all your videos.
Wow, that was fascinating indeed! I didn't realise until now that the bubbles were gasious water due to the reduced boiling point at lower pressures - that is pretty fascinating!
A boat tug of war between paddle and propellor powered warships is the most badass thing I've seen today. You could've gotten the point across with smaller vessels but the British don't joke around with their naval power
Very interesting! Never thought of why small airplanes like Cessna most often have propellers with two blades and four if they are big enough. But apperantly they do also have airplanes with three blades propellers.
Each extra blade does add more bite, but also increases drag.
One thing you absolutely forgot to mention. On military craft, the number of blades on a prop are typically a prime number, to eliminate any primary resonance during operation. 3, 5,7,11...etc.
I remember being told at school a single blade is technically most efficient. And this is the first time I've seen it in video. Submarines seem to keep their propeller designs secret but the ones i have seen do have many blades.
I thought this is just hydrodynamics but then found "Propeller Theory" article on Wikipedia, realizing it's an actual thing. Wow. Always learning something new.
I like how you showing the different types of fan blades but would love to see a comparison with 3 4 blade one.
1:02 "ships mechanized rowing" is the perfect way to explain steamships and I've never heard that till now wow
Wow!
Far more complicated than I would’ve thought beforehand
Excellent. CZcams should make two layer videos, where the first layer would remain your excellent and enthusiastic presentation and if 2nd layer is checked then in the video parts skipped by layer1 setting you could explain some of the physics.
Fascinating indeed! That's just WOW!!!
Truly facinating stuff !
This video has propelled my knowledge.
Not sure why I needed to know this but I certainly won't forget it
Excellent topic, nicely covered. You may need to do a follow-up to cover toroidal props. Cavitation is fascinating to me. As a little kid, I always wondered where all the bubbles were coming from when I ventured out into the bay in a friend's small outboard motorboat. Oh, and how about mantis shrimp--they can cavitate the water.
With outboard powered boats most of the bubbles are exhaust gases from the engine. Basically the 'standard' design for an outboard is to mix the exhaust with the used cooling water, then dump both through the hollow propeller hub. Some smaller outboards instead have an exhaust outlet just above and behind the propeller, but they still mix the exhaust with the coolant and then dump both underwater.
The main reason for this is that it makes the engine quieter for the passengers (local sea life might disagree) and reduces the amount of smelly fumes (once again, local sea life might disagree). Another advantage is that at high speed the slipstream of the propeller hub can create suction that helps pull the exhaust out of the engine, improving performance.
Cool video! never thought of this.
Idk how I found your channel, but it helps me sleep at night
great video!...thoughts on the Sharrow props?
I like the attention to detail with the smoke towers 5:08 :)
Fantastic video! Could you explain the effects of accelerating/decelerating dutches and counter-rotating screw?
Very interesting, thanks!
I like the amount of detail for the titanic, making the 4th funnel produce no smoke.
Another "completely different" design, the Voith Schneider, is optimized for maneuverability. The axis of rotation is vertical, blades aren't screw-like, but more like hydrofoils, and the drive design is a bit like the cyclic part of a helicopter. They've been used on some tugs and ferries, including the Staten Island ferry
fun and educational.and short!very good!
This stuff is so fascinating
Great video! 🎉
Then you add variable pitch propellers that can change their profile depending on water velocity. Such a complex and cool science
Math, so amazing, so mind-boggling. No wonder I kept falling asleep in class (that, and it was right after lunch so I felt sleepy)!
Man.....hearing about cavitation for the first time here I read up on it and found out that joint cracking happens because of cavitation as well. Super interesing.
Good boost to my ego assuming the difference was vibration. Still learned something.
Good video. I think sharrow propeller as an interesting development. Will see when it comes to a bit bigger boats and ships.
very good video that is a question that i would really understand but now i know exactly thanks
Casual Navigation, would you consider doing a video about the new toroidal propeller shape made possible by 3d printing and its application potential?
Fascinating!
A bit like an end mill.
A 3 flute can take as much material off an a 4 flute but to do that it either needs to move at a faster feed which loads the flutes more, but that can be minimized with a faster speed but that increases stress on the cutting edge while reducing chip load.
1:20 I like the design you choose for the H.M.S. Rattler and H.M.S. Alecto.
It works very similar with propellors on planes too. Again anything from 2 to 6 blades is common. Whilst cavitation isn't an issue, the blade tips need to avoid going supersonic which restricts speeds, but by having more blades the props can rotate slower whilst giving the same power output, so faster planes tend to have more blades (and you can even double up with contra-rotating props like on the fastest prop driven plane the TU95 Bear). The downside is the same as ships though. More blades means more powerful engines needed to turn them at the same speed, and more drag in the event of an engine failure (although generally anything with more than 2 blades will have variable pitch blades which can "feather" to reduce drag, and those with lots of blades tend to have auto feathering in the event of a shutdown).
The Spitfire provides a good example as it started off with 2 blades and eventually evolved to have 6, getting a more powerful engine and higher top speed each evolution.
Subs: You think your propellers are complicated.
Also subs: We can have blades numbering in the double digits