Why Are 4 Blades Better Than 3? 

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.

*_Props_* to Casual Navigation for bringing this to our attention. 😉

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.

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

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.

Kudos to your animation of the Titanic not having smoke come from the fourth funnel.

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

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.

Once again the parallels between aviation and seafaring are uncanny. Very well explained and animated, as always, Mr. C.N.

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

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

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!

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.

i would love a deeper dive into propeller theory

Cutters for milling machines and similar have the same challenge; more edges on cutters has costs and benefits.

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 wouldn't know how interested I am in this stuff without this channel existing. Thanks.

these videos have a rediculous level of quality. Soo good. Technical depth and animations everything is on point. Big fan!

I appreciate your attention to detail, the animation shows smoke emitted from only the front 3 funnels, which is accurate indeed.

A single-blade propeller wobbling the ship to bits? Sounds like something the kerbals would do.

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 have absolutely enjoyed this quick introduction to the topic. 👍👍

I like that the animation at 0:40 shows smoke coming only from the first 3 chimneys. Nice attention to detail.

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

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.

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.

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

This is a beautiful elegant explanation of propellors.

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.'

Another question::Why not 100?

Really cool vid. Thanks for uploading!

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!

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.

Amazing video - what a wonderful explanation presented so succintly!

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!

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?

60 tiny blades is the best.

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.

Thank you for teaching me this information I never needed to know.

4 blades help give more speed when leaving

you should do a video on Voith Schneider Propellers, they are very strange.

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.

Before playing the video it would have never occurred to me that you could make such a subject so fascinating.

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

Thank you for the explanation. Can you make a video about toroidal propellers?

4:09 That explains why submarines have propellers with many blades. Each additional blade reduces the noise!

Exactly the level of explanation that I needed!

Would be nice to see also the toroidal propeller im comparison

Steel? Bronze more common…

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!! =)

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 )

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?

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

Fascinating indeed! That's just WOW!!!

20 seconds ago

Love this channel it's just "Wanna know something random" And it just fits on youtube

Truly facinating stuff !

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

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.

fun and educational.and short!very good!

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...).

Very interesting, thanks!

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.

I like how you showing the different types of fan blades but would love to see a comparison with 3 4 blade one.

Cool video! never thought of this.

This video has propelled my knowledge.

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.

I like the attention to detail with the smoke towers 5:08 :)

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.

Idk how I found your channel, but it helps me sleep at night

Wow! Far more complicated than I would’ve thought beforehand

good casual navigation 👏

Not sure why I needed to know this but I certainly won't forget it

Great video! 🎉

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.

great video!...thoughts on the Sharrow props?

1:02 "ships mechanized rowing" is the perfect way to explain steamships and I've never heard that till now wow

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

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!

Very nice !

very good video that is a question that i would really understand but now i know exactly thanks

I like the amount of detail for the titanic, making the 4th funnel produce no smoke.

Fascinating!

Fantastic video! Could you explain the effects of accelerating/decelerating dutches and counter-rotating screw?

This stuff is so fascinating

Best vid yet!

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

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.

1:20 I like the design you choose for the H.M.S. Rattler and H.M.S. Alecto.

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.

Great information - Thanks ! What is about turoidal props ?

Casual Navigation, would you consider doing a video about the new toroidal propeller shape made possible by 3d printing and its application potential?

I’m a big fan already

Good video!

Excellent. RU-vid 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.

Good video. I think sharrow propeller as an interesting development. Will see when it comes to a bit bigger boats and ships.

Then you add variable pitch propellers that can change their profile depending on water velocity. Such a complex and cool science

Props to this