Left Handed Ships? - The Effect of Transverse Thrust on Ship Handling

[@0cs025]

I love the subtle engine sound whenever the animation comes in, its so soothing!

[@CasualNavigation]

Cheers Joshua. Glad you liked the noises

[@tk4x431]

And the little truck going around at the port!

[@tonyellen_]

You probably love the sound of the ambient hum of a starship engine in the background. If you've never heard it...kzbin.info/www/bejne/kIHSooGbh5iSi6M

[@eurybaric]

@@tonyellen_ never knew i needed this. thanks!

[@denverflatpackjedithornton]

@@tonyellen_ you're mad

[@connorjohnson7834]

So if a ship has two propellers spinning in opposite directions, is she ambidextrous?

[@software_opal]

From Wikipedia, it seems that they are called 'inward turning' and 'outward turning'

[@popcornegg4405]

Connor Johnson 🤨 🤔

[@peggyt1243]

... that is how ships/boats pivot in place. Bow thrusters make it even easier.

[@thegentleman1398]

Illuminati confirmed

[@F.R.E.D.D2986]

That would make her go forward and reverse and the same time

[@Dante_Alighieri1321]

Honestly this channel is incredibly interesting. I never knew I had such a fascination with maritime activities.

[@CasualNavigation]

Thanks Dante. I was hoping to broaden the appeal of maritime topics

[@kgm1939]

Casual Navigation honestly. I never knew ships could be so interesting aswell :D

[@ThZuao]

The effect also occurs in planes. Don't know to which degree they are related, but the effect is there. It's not called Propeller Walk, but rather Propeller Wash. Seeing from the pilot seat on a puller (standard) configuration single engine, single prop aircraft, the vortex-like air coming out of the propeler tends to induce higher lift in one side of the wing root and lower on the other, along with an effect on the rudder. This makes the aircraft roll to one side, but the effect is minor and easily corrected by trim adjustments. Some people got a bit creative on addressing this problem. In high performance, high power/weight ratio aircraft like WWII Fighters, usually the rudder had a preset angle of attack to compensate propwash. But the Italians went a step beyond and made a few warbird models have a wing longer on one side than the other. Another effect present in high power single engine aircraft is the P-factor in which the torque of the engine tends to make the plane yaw to one side while on the takeoff run. Easily adressed by applying some pressure to the pedals (that also control the tailwheel, if unlocked). Gyroscopic effects are also present in propeller aircraft. The effect is barely noticeable today, but in the times of Canvas and Wood planes (think WWI), the spinning mass made planes a bit hard to land. Especially the Sopwith Camel. They put a rotary engine in it (the engine block rotated instead of the crankshaft), so it had a lot of spinning mass in a light plane that made the gyroscopic effect quite pronounced. The Camel was notorious for being hard to land, as due to gyroscopic precession, the plane pitched up while rolling to one side and down rolling to the other. Pilots soon learned the proper combination of pitch and roll to apply while landing, but the Camel was only flown by the most experienced pilots and still had a higher crash on landing rate.

[@JohnSmith-nz4bn]

I'm blown away by this fact 😏 sorry couldn't resist! Always wondered about that too. Makes sense now you've explained. Thanks man!

[@skymcdaniel9513]

torque roll

[@rockstarpl0x423]

The Phak calls it the left turning tendency. It’s actually really fun to overcome especially during windy condition at slow speeds

[@Sableagle]

This is why spitfire pilots have to start a take-off run with the left foot all the way down on the yaw pedal. That huge engine in that little plane did its best to stand the plane on its starboard wheel and spin it in circles, and if you open the throttle past about 30% it'll pull you over onto your nose instead. Performance like that is not easy to control.

[@djnokes1818]

"Right rudder!"-cfi

[@gregculverwell]

100% good explanation. I'm always amazed at how many boat owners don't understand this and therefore struggle to dock their boats.

[@MervynPartin]

When we did sea trials on a new-build gas carrier in the 70s, the ship had a very pronounced tendency to turn to port when going ahead under power. The joke at the time was that the hull had been built banana shaped! I guess the deck department learned to live with it. Thanks for your clear presentation

[@Cragified]

New class of ships tend to bring lots of interesting quirks to the surface. The two North Carolina class battleships ended up going through if I recall correctly 11 different propeller configurations combined to solve the vibration issues.

[@Quasihamster]

Are left handed ships more creative than right handed ones?

[@BeKindToBirds]

It's an urban legend

[@alexnutcasio936]

NO, but they spell better!! Sorta like 5 ways to spell a three letter word??

[@lunatickoala]

Not necessarily but they're definitely more sinister.

[@fidelcatsro6948]

my left pawed cat says you spelt a word wrongly

[@alexnutcasio936]

@@fidelcatsro6948 that cat is still struggling with spelling.........Spelt??? As in past tense of spell.

[@sr-71android27]

One question, what if a ship has two counter rotating propellers? does it just cancel out the effect?

[@albertbatfinder5240]

Sure does, but there is another factor to consider. Do the two counter-rotating props spin “out” or “in”? (“Out” meaning starboard prop clockwise, port anticlockwise, and “in” being the opposite.) “Out” configuration has wider thrust lines. (Imagine the water flowing further from the centreline). Gives better turning ability, especially when using engines alone to manoeuvre. “In” advantages include better efficiency, especially if the boat can plane. The stern tends to sink with inward rotation, thus lifting the bow.

[@D8W2P4]

@Richard Hunt Ambidextrous.

[@kenlee9874]

@@albertbatfinder5240 Thanks-excellent explanation of hydro-dynamic forces acting on the hull. Thanks

[@ajg7810]

Surprisingly it doesn't. You'll see that ships are always a bit lefty or righty, meaning that they'll tent to go bow to port or stb when doing headway.

[@colonelstriker2519]

I want a follow up vid regarding this

[@fecu2394]

I never knew boats were so fascinating. Thank you.

[@JonasAlexanderson]

Not to be confused you call a (left handed) pitch propeller as "acting like a right handed". Also taking a tight corner or turning round a buoy it's easier to turn with this force. Remember that a fixed propeller, right handed, turn best to port when the propeller is working ahead and to starboard when it is working astern. A pitch propeller (acting right handed) is turning best to starboard on both ahead and astern. As you say in the video this can help a lot during maneuvering. Great video and very well explained.

[@TheGamingTechs]

Please make a video on why hulls are typically colored red!

[@NoNameAtAll2]

You were the only comment loaded for me

[@AVIATIONB-a]

NoName Yeah

[@CasualNavigation]

Nice idea The Gaming Techs. I'll add it to my list

[@Quasihamster]

Wasn't it a corrosion retardant color? I know Robert Ballard suggested painting the wreck of the Titanic with that a few years back to make it last longer. Made me wonder whether he remembered she had water inside her as well...

[@TheGamingTechs]

Casual Navigation Any plans on posting weekly? That would be a dream! Thanks for the awesome content!

[@odehrizkallah395]

This channel is a goldmine, the knowledge as well as the trivia every now and again is proving important to me, a high school junior who is looking at doing something like this in the future.

[@CasualNavigation]

Glad you like it Odeh. It's great to hear you are looking to a future in the maritime industry

[@naveenraj2008eee]

Wow.. Never heard of ship being left or right... Interesting to learn... Thank you....🙏👍😊

[@chris77777777ify]

He’s lying. Don’t be a fool & believe everything you hear

[@pxsrrail2558]

@@chris77777777ify no he's not, this is logical and scientifically proven

[@aigberadioninnocent4380]

The simplest and very educative animation have ever seen on propeller rotation.Thank you.very helpful

[@duchi882]

*Didn't know about this* _The More You Know_

[@johnkelley9877]

I had never known about a ship being right or left handed until I watched this. Thanks for sharing this, I learned quite a bit.

[@MrGas00]

The animations are superb, as well as the explanations, great video.

[@marinepilotchris3048]

This is a great channel! I hope you don’t mind but I’ve been answering a few questions from others in the comments. Keep up the good work!! Chris - Marine Pilot

[@GolfKilo]

Dank der guten Animationen kann man das Video auch mit geringen Englischkenntnissen verstehen. Sehr gut, danke!

[@ukar69]

I was once piloting a leisure boat on the Norfolk Broads, which are tidal. I needed to do a 180 and no matter how hard I tried it wouldn’t turn round in the available width. I then tried turning in the opposite direction and it went round without a problem so I’m guessing it was to do with the effectiveness of the rudder/propellor against the water flow.

[@CasualNavigation]

Could well be. Often ships like to turn one way more than the other. When I do a turn, I wait to see what way she wants to turn then just go with it

[@marinepilotchris3048]

Paul Osborne you’re almost certainly correct. Although, it’s not always possible to swing a ship the way it ‘wants’ to swing for many reasons. Letting go an anchor in a tide is a very effective way to get a ship to swing if the tide is astern of you as it will hold the bow more or less in the position that you dropped the anchor. If the tide is ahead of you then get stopped over the ground with the tide ahead, (stemming the tide) then put the rudder hard over while using short burst of power ahead (kicks) this will prevent you gaining much headway while ensuring the maximum turning force, the tide will start to push the bow around and the kicks ahead should hold the stern up again the tide and thus able to turn a vessel in its own length. Transverse thrust is a valuable tool to use for ship-handling, and on most occasions it can be used to your advantage. Chris - Marine Pilot

[@al1rednam]

I know I'm late... Leisure sailor and motor boater from Germany here. I was taught this effect from the very beginning. My first instructor (who happens to be my father and does instructing as a kind of side hustle) always teaches this bit. And on every voyage it is one of the first things we find out. We usually charter sailing yachts so it is a new ship to us most of the time. And not only on voyages with one or more people in training but on every voyage we do some maneuvering trials on the first day to get a better understanding of the ships handling. Turning on the spot is one of the staples, as it a) is useful information for getting out of tight spots and b) it tells us which is the "chocolate side" (from German "Schokoladenseite", like sweet spot) for being alongside. We prefer to have the prop walk pull the aft in. As a further aid it pulls the boat parallel to a dock on leaving after steaming into the fore spring. Very relevant for sailing yachts: the strength of prop walk is very dependent on hull geometry and prop placement. Extremes are a) old ships with a long keel and the prop behind the keel and the rudder behind the prop. Engine running backwards with little speed through the water don't react to the rudder at all. B) modern yachts with a short (but deeper) keel, flat bottom and a saildrive near the center (lengthwise) experience hardly any prop walk. In my opinion it comes down to seamanship. Know your vessel and use that knowledge to your advantage.

[@ryans.5998]

As a pilot, I find this channel extremely interesting. The similarities are obvious (two crafts moving through a fluid), but it’s still cool to see this perspective. In a single-engine aircraft with a propeller, we fight left-turning tendencies from a clock-wise rotating prop with right rudder. Instead of the “twisted” water pushing against the hull, we have the spiraling slipstream from the propeller pushing against the vertical stabilizer, which kicks the tail to the right and the nose to the left. We also have torque (Newton’s Third Law), gyroscopic precession, and P-Factor from the prop that all try to yaw the airplane to the left. Just subscribed!

[@1111757]

Hi! it's me, a guy how's been a passenger on a ship maybe 6 times in his life, watching everything there is to know about ships on youtube.

[@nlo114]

Very informative thank you. Now I know why some 68 foot narrow-boats handle like a shopping trolley in reverse!

[@grancito2]

But they are flat bottom, so his bullshit doesn't apply. The effect is water density difference, well known except by him.

[@viknesh6569]

This channel is a treasure trove of ship knowledge dare i say essential.

[@bas6983]

In general a cpp equiped vessel will be called by the result. Ie a left turning cpp is “right handed” one of my collegues is always telling a pilot. “The ship has a left turning, right acting cpp” Many thanks mentioning the fact the stern comes in and its not the bow moving out.

[@marinepilotchris3048]

Bas Great comment! I’m a pilot and I only want to know which way a ship acts when going astern. When I hear ‘CPP, right handed’ I always have to verify which way it acts, as sometime there can be a misunderstanding as to what will actually happen when I order the engines astern, until it’s too late!

[@Captain_Flippers]

This channel is a godsend to me and anyone on my maritime academy in Antwerp Cheers!

[@CasualNavigation]

Thanks That guy. Glad it helps

[@Captain_Flippers]

I’m currently in my exams and your video series of the colreg light signals and sounds have been extremely helpful. Again cheers man! Channels like your are rare to come by!

[@Kyrinson]

hmm.. with me being left handed... does that mean if I walk backwards then I will tend to drift to the right? :)

[@CasualNavigation]

I would assume it does :)

[@RoadRunnerLaser]

Typically, yes (if you have no other means of guidance). People tend to walk in circles if they are not relying on an external means of guidance. If you were out in the desert intending to walk in a straight line (or were out in a wide-open area with your eyes closed), for example, you will walk in a large circle determined by your dominant leg. If you are right-handed, you will tend to make longer, more powerful strides with your right leg, causing you to turn to the left.

[@michaellinehan710]

I learned all about this on my Basic OOW course on 2015, but it didn't truly make all that much sense to me until I took the Port ASH navigators course last year. Driving mini ships around is a great way to understand the forces involved. Especially considering I've only ever driven twin CPPs, a single FPP berthing with no tugs becomes remarkably simple after learning how to use Paddlewheel Effect properly!

[@20PhantoM07]

You’ve just explained something to me that I’ve been wondering for years, now I know how the long ships get to dock up the river near where I live in Port Talbot, thanks.!

[@ismael5902]

Great video man! I didn't knew I had this question until now😂💪

[@CasualNavigation]

Cheers Ismael. Always glad to give answers to unknown questions

[@grancito2]

He gave a false answer.

[@ismael5902]

Then show what would be your answer, we are here to learn.

[@grancito2]

@@ismael5902 It is common knowledge, in the boat community, different water density between the top and the bottom of the propeller, more side thrust from the bottom. It is evident when going forward, as well, the steering pulls to one side, outboards have a trim fin behind the propeller to help compensate.

[@mikefochtman7164]

Grew up piloting small boats before I could drive a car. One uncle had a nice twin screw, that was so easy to dock and maneuver, just shift each shaft fwd/rev as desired to twist around anyway I wanted. But my other had an inboard, right-hand single screw with a rather small rudder. Docking port-side to, was easy just as your video shows. But backing out of the slip was a bit tricky as the rudder had much less effect than the prop-wash until moving pretty fast (didn't matter how I turned the rudder, it would always back around, swinging the stern to port). Then modern boats started getting inboard/outboards. Higher power of larger inboard engines, maneuverability of outboards with their directional props. I/O units are a bit like the small boat version of anzipods. :)

[@robertbrouillette6767]

As far as I know, merchant vessel cargo ships have right handed propellers and this is done by convention. So when you get an astern bell, the ship will have that swing to port side. Cruise ships may have twin screws ( I am not sure ) and military ships have variable pitch propellers. Ships have bow thrusters to help in docking and usually two tugs, one at each end ( bow and stern ). Most of the ships I have worked on are usually port side to the dock except Roll On, Roll Off ( Roro ) where they are tied starboard side to.

[@besacciaesteban]

Another way of knowing is "putting" your thumb's tip on the proppeler's axis end, and see if your fingers can point the direction it is rotating.

[@jlittlenz]

Indeed, the video might have explained why it's called right or left *handed*. It's like right or left handed screw threads.

[@irohaboat]

I was on a 100-120ton, single screw, cargo pitcher for 3 years. The Skipper would mention about the ship walking as we left and and came in to dock. Never fully understood why. Thanks

[@kennedymcgovern5413]

More on Navy ships, just to add more interesting info: I cannot speak for other countries, but US Navy ships have "reversible pitch propellers." What this means is, you don't have to slow down the propellers at all. You can "shift into reverse" at full speed, just by changing the pitch. Using this system, a Destroyer, which clocked in at 563 feet (Spruance class, from my day) could go from Flank 3 (full speed) to full stop...in a single ship length. It was like hitting the "brakes." It was neat when we'd do it. The ship would just instantaneously jerk itself back in the water (sending everything that wasn't battened down flying) and the bow would lift out of the water so high that the top of the Sonar Dome was visible. Also, you could actually pull a Navy ship pierside, without tug boats, because of the added maneuverability. This was not done often. We usually had the tugs come out. But on occasion, when the Skipper was training a young officer, he'd make that young officer do it.

[@Danieloncarevic]

Great video. I'd just add a short mention on 2 propellers and the effect of cancelling each other out when running astern. If you care about an idea... how bow thrusters work could be interesting to people not knowing about them. In cases with only one but also multiple ones on the bow and stern as well... Cheers!

[@CasualNavigation]

I do plan on getting to bow thruster some time

[@SquareCanine]

Brings to mind the importance of knowing what type of thrust reverser you have on a Sea-Doo (PWC). I wouldn't be surprised if, for the sake of consistent steering as a safety issue all sea-doos now use a reverser mounted on the thruster nozzle that just redirects water roughly 180 degrees. Since there is a thruster in the way, this type of reverser actually directs water mostly down at an angle, under the thruster. This reduces reverse thrust and steering authority substantially, compared to normal operation when going forward, but means the craft steers in reverse like other motor boats (and cars). The side you steer to will always be the inside of the turn, and the end of the craft moving forward will steer to that same side. I don't know if they're still used, but older sea-doos (some at least) instead have a wide deflector attached to the hull that acts more as a mirror. It's shaped to redirect incoming water primarily to the sides, but angled forward. Thrust strait backwards is, Id' say better, but not by much. The thrust is largely to the sides and wasted cancelling itself out. However, turning authority in reverse was *excellent*. The deflector could push water at a more sideways angle than the thruster itself could turn. The "downside" is that reverse steering is inverted. With this scheme, the bow always turns to the side your steering in either direction. Put another way, as viewed from above, steering to the right always turns the craft clockwise, and steering left always counter clockwise. I actually found this pretty intuitive for this specific kind of craft. Delicate maneuvers usually involve alternating between forward and reverse thrust while your body is turned around. Having the steering controls always spin you the same way regardless of what way you are facing or where the thrust reverser is set removes any mental frame of reference issues, and also results in a lot less sea-sawing the steering (which otherwise needs to be reversed in tandem with the reversing lever to maintain a direction of spin).

[@alexnutcasio936]

This is why most modern vessels have counterrotating props. The large majority of small power boats, IO (stern drive) , inboard or outboard, are right handed. that is unless of course, they have dual engines with counterrotating props.

[@matthewrobinson4323]

Excellent video. Question: What about a ship with multiple screws? Say one right-handed, and one left-handed? I know a ship with twin or quadruple screws can be steered with the screws alone if the rudder is inoperable, and it would seem that with one side right-handed and the other side would be even more so. Am I correct in this assumption?

[@marinepilotchris3048]

Matthew Robinson props turning in the same direction are rare, but they do exist. Usually props turn in opposite directions as you say. They are described as inward turning or outward turning. It’s important when ship handling to know which way the twin props turn. As for transverse thrust, twin props turning in opposite directions often cancel each other out, but there are many factors that can make the ship act slightly left or right handed even with twin props. Chris - Marine Pilot

[@matthewrobinson4323]

@@marinepilotchris3048 Thank you.

[@gmcjetpilot]

There is P factor where prop thrust is not at shaft but slight to left or right because relative angle of attack due water movement.

[@catwithshotgun333]

You learn something new every day

[@emeraldqueen1994]

So, right or left propped (using propped to mean handed) are a thing, but what about ambidextrous ships?

[@aaronwalderslade]

The best way to remember this is to imagine the propellor as a tiny paddle steamer. It will indicate the direction of the stern's movement. In fact some people call it the paddle steamer effect since that's what it looks like it's doing, even though other forces are also at work.

[@terrytytula]

Excellent video, explains an aspect of vessel performance I never Knew existed.

[@bestcomdand7023]

Excellent info on the neg n pos pressure at the props -first video I've seen that explains this. Thanks.

[@evergreenappreciator]

Interesting explanation, I'd never thought of it that way. I was taught that right hand props back to port (bow goes to stbd) because of a so-called "paddle wheel" effect. Wherein, due to the pitch of the propeller, the blades grab water from the port side and draw the stern over to port. Similar to how a paddle wheel steamer creates forward motion.

[@CasualNavigation]

It does do the paddle wheeling too, simply due to the different densities between the water at the top and bottom of the propeller. A ship in ballast will suffer more because there is a bigger percentage difference than if the ship is deeper

[@hasegawaarisu5678]

Do you get this tendency with multiple props? as I assume you can make double props turn into each other (counter rotate)? or do they still have a right/left handed?

[@CasualNavigation]

You still get it, but often one is right handed and one is left handed. When both run astern they cancel eachother out

[@nattygsbord]

Its like on airplanes such as P-38 Lightning then. When each propeller turn outwards they cancel each other out so that the plane stops turning to the side as a single engine propeller aircraft normally do.

[@Haku1610_Arts]

What if a ship has even number of propelers say 2 or 4, as the props cancel each other out, can you still consider it left or right handed?

[@CasualNavigation]

With twin screw, you often call it either inward turning or outward turning

[@WIRRUZZZ]

@@nattygsbord Although this is not the case for all twin engine aircraft. Many have props rotating in the same direction (means you can use the same engine / props on both sides). That gives you a "critical engine", i.e. one where a failure is more difficult to control (or something like this, I only fly gliders, so no engine issues for me ;) )

[@paterson00]

Great explanation with great animation as always. Thank you for doing this.

[@kauske]

I have to wonder how pronounced this effect is in three screw ships, since in twin screws, making them contra-rotating cancels everything out. But with an odd number of props, that would be harder. I also wonder if props with a duct around them mitigate the effect too.

[@minivegas6791]

I thought the visualisation for the propeller pushing water was really well done 👍

[@napster7825]

Very interesting, I try to learn something every day, now I have. Thanks

[@CasualNavigation]

Glad to help Jack

[@ZioStalin]

Similar to torque steering in cars. Enough said. Planes have this issue as well. But it can be compensated by having two screws/props per engine rotating in opposite directions or an even number of engines rotating in opposite directions.

[@pgnandt]

If there is an approach angle to the prop shaft you can now enter in P-factor. Tendency to turn to port causing you to rudder to starboard. This gives you a stable heading. Boat wont wag left and right.

[@JavierCR25]

Man, this channel grew in me so quickly...

[@dwoodkamp4550]

Fascinating didn't know that, but has it also affect on an azipod propeller which turns left or right??

[@marinepilotchris3048]

D woodkamp great question, an azipod still has transverse thrust like any other propellor. Although changing the pod angle can produce differing results. Usually an Azipod’s thrust is left in one direction (ahead) and the pod is rotated to provide thrust where you want it. Chris - Marine Pilot

[@researchcapt]

Yes, but the direction of the wash from an azipod is very precise.

[@chrislynn4940]

Water density increases very quickly with increased depth. The propeller blades produce more sideways thrust while they are more deeply submerged. This effect of this is much more noticeable when going astern. Most ships and boats are right handed, so the stern will be pushed to port.

[@generalcodsworth4417]

Is there any effect if there are two propellers spinning in opposite directions?

[@marinepilotchris3048]

Most often they cancel each other out, but sometimes they can act either way. Small differences in the pitch of a propeller or when a ship is leaning over slightly (listing) can produce different effects. Chris - Marine Pilot

[@chaabounioussama3977]

the propeller walk or transverse thrust can be explained also by the difference of the resistance of water on the upper blade which is less than the resistance on the lower blade due to the difference of pressure of the water, I think that is a better explanation than the effect of the blades on the ship's hull

[@HungryGuyStories]

Can you eliminate this behavior by having two counter-rotating propellers?

[@jonathanspinks9242]

Untill inevitably you stop one engine in the final approach

[@HungryGuyStories]

@@jonathanspinks9242 Well, it's a boat, not an airplane. If one engine fails, you're just running in either lefty or righty mode, and you have to be extra careful not to do this: kzbin.info/www/bejne/pp_dmGONp8ShfLs

[@jonathanspinks9242]

@@HungryGuyStories I meant on approach to a berth, most twin screw ships will stop one engine before the other to help turn the ship ie angled bow-in to a port side berth, you would stop starboard so the port engine helps swing the stern in

[@HungryGuyStories]

@@jonathanspinks9242 Oh, okay. That makes sense now :-)

[@bitsnpieces11]

Makes good sense for having contra-rotating propellers on ships as well as aircraft since the forces would tend to cancel each other out.

[@dankuchar6821]

If you can explain why aircraft carriers lean the "wrong" direction when they turn fast, I would love to know what that's all about. Thanks!

[@kyledavis4890]

A guess, but probably to keep things on deck on deck. Sure the planes and choppers are usually strapped down. But...

[@cartersense]

Always stuff to learn, that I don't even really need to.

[@ph11p3540]

Would this still apply to a military ship with two or four counter rotating propellers? What about ducted Kort Nozzle Propellers? What if the propeller cavitates?

[@CasualNavigation]

Twin screw will cancel the effect. Also, kort nozzles do minimise the effect too

[@woolfoma]

ambidextrous ships (No idea if that's a real term :P ) do not suffer from this effect, but can also use differential thrust (usually possible for the class of ships you were talking about) to receive even more turning power than this provides if needed. as for the other things mentioned, hopefully another commenter knows enough to speak on that.

[@erictaylor5462]

The same thing happens in (propeller) airplanes. The air coming from the propeller is twisting as well as moving to the back of the plane. This introduces a roll factor that must be corrected. There is also a torch factor, caused by the engine.

[@Saviliana]

Then what about twin motor twin propeller boats that spins different directions ? Are they different?

[@SethKotta]

Quick question: what would cause someone to want a left handed ship over a right handed one?

[@pizzapower95]

maybe if a ships home port would be easier to dock whit a left handed.

[@skeleskele]

I feel like im watching a pirate teaching me about ships... That navigator language tho

[@iangomes]

Neat! *Goes to click the like button, but realized I have already watched and liked*

[@ianbelanger7459]

While this is another great video, the explanation is a little oversimplified. What follows is simply a more technical breakdown and not meant to detract from the wonderful work of this channels creator. The term "prop walk" is more properly several effects, which act while operating ahead and astern. Several other commenters have brought up P-effect and gyroscopic procession, while the video covered hull effects and mentions transverse trust. These are all different effects with different impacts on handling depending on environmental conditions. Hull effects were described wonderfully in the video. The only note is that single screw ships also have to account for the force when sailing ahead in calm water. It is almost never an issue because in the real world the wind or waves have a larger impact. Transverse thrust, while mentioned, is more technically a totally separate effect from the one described. Propellers without a duct, shroud or nozzle simply produce thrust in the axial direction and because there is slightly greater pressure at the bottom of the propeller there is a little transverse thrust in one direction. Depending on propeller design, this effect can be 5% of the thrust pushing the ship. P-effect, mentioned below, is something commonly understood by pilots because it is caused when a propeller is not faced directly into the flow of air or water. Most ship propeller are angled, so the flow of water does not hit the propeller squarely which causes a torque on the ship. The direction of the torque is determined by the rotation of the propeller. Gyroscopic progression is the shift in direction of an applied force. Because the propeller can be considered a spinning mass and is usually at an angle to the water flow, the force of the water interacting with the propeller applies a torque to the ship. Lastly from a ship handling standpoint, prop walk is important because the effects are out sized when moving slowly. This is especially important when maneuvering astern because the rotation point of the ship moves from about a third back from the bow (while moving ahead) to the rudder post (while moving astern). It is this combination of dynamic effects that makes precise maneuvering such difficult a skill to master.

[@rubes3927]

Why is this channel so entertaining? 🧐

[@quillmaurer6563]

So it seems the effect is most relevant for when the propeller is running astern, which will depend on the handedness and if it's a fixed-pitch or variable-pitch. I'd think it would be simpler just to consider the direction the propeller turns when running astern, regardless of whether that's a variable pitch propeller turning the normal direction or a fixed-pitch turning backwards. Likewise, is there any effect while running forward of the propeller "P-factor" if the propeller shaft is not horizontal, as is fairly common on smaller boats? This is commonly discussed for airplanes while climbing, one side of the propeller is effectively grabbing more air because the airflow and propeller aren't square to one another. I'd imagine the effect to be smaller than on airplanes because the propeller is much smaller relative to the vessel than an airplane's propeller is relative to the plane, but still present and probably noticeable.

[@CasualNavigation]

I hadn't considered the effect of not being horizontal. Would be interesting to look into though

[@akamalesh8512]

If a ship has two props then. What would be the case . Would both the props would be Right or left handed.

[@TristanMorrow]

Is this transverse thrust effect more or less pronounced with the variable propellers?

[@CasualNavigation]

I haven't ever noticed one be more pronounced than the other when at similar speeds

[@TristanMorrow]

@@CasualNavigation Ah, interesting - thanks for making all the great videos!

[@lisamangles4878]

Good stuff !!! Keep it comming.. and thx

[@JohnJohansen2]

Also the difference in water pressure from the upper blade and the lower blade on the propeller, has some significance.

[@zamnodorszk7898]

Love your videos. Can you make a video on why propellers always have to be at the stern of the ship?

[@Sableagle]

Maybe because when the ship thrusts forwards the stern goes deeper, allowing more force to be applied, while the bow rises up, reducing the available force, like how drag-racers are rear-wheel drive.

[@zamnodorszk7898]

@@Sableagle Of course, hadn't thought of it that way! Would be interesting to see the mechanics of the torque incurred by the prop to cause such a downwards motion.

[@macattack123mattc3]

@@zamnodorszk7898 Bit late, but for the future: It's the same as in airplanes like the 737. The center of mass is not in line with the thrust vector. That offset results in a torque which will cause the plane to pitch up as you increase power. It's probably the same effect in boats. Of course, in planes there are a lot of other factors at play like the control surface trims, and your load...

[@johnmeyers3954]

Thanks for explaining that it is the propeller wash hitting the bottom of the boat/ship that forced the lateral movement. I had wondered if it was due to the higher water pressure at the deeper level that caused the propeller blade to have more resistance thus causing the lateral movement away from the propeller blade's movement. Has anyone tried to test this pressure theory in a tank where there is no hull to push?

[@illfox240sx6]

what if a boat has two propellers turning in both directions what would that be called and would it negate propeller walk

[@CasualNavigation]

That is twin screw, and yes, if they are both running then the transverse will cancel out

[@illfox240sx6]

well thank you very much for the reply

[@owl725]

my favorite channel

[@TheSilmarillian]

Nicely explained I had never thought much about propellers wonder if the left handed ones are smarter :)

[@jannejohansson3383]

In Finland we captain the vessel, not otherwise. It's called Azipod ABB.

[@minkyone]

If a ship has two propellers, one left-handed and one right handed then the ship could "drif" is both directions by just spinning one propeller more than the other or stop one completely. Right?

[@CasualNavigation]

Right

[@bluehampar]

I once had to manouver a small diesel pwoered "snipa" which had almost no rudder so the transverse thrus made it so that you really only could turn in one direction

[@TheWaynester101]

Hello! I have a question, does this also apply to boats wth two propellers?

[@marinepilotchris3048]

It does.....but often two propellers often rotate in opposite directions therefore cancelling each other out. Twin props that turn in the same direction are rare, but there are a few out there. Chris - Marine Pilot

[@74836]

What about triple or quadruple propellers

[@fixyfoxy2661]

How do companys who build ships decide if they want to build a right or left handed ship? Is this random or do they look at certain factors?

[@marinepilotchris3048]

Fixyfoxy usually when a ship is planned to be built the Naval architects will construct a model to study the hydrodynamics, it is at this point that they will see which rotation suits the hull form best. In my experience out of all the single prop ships I have piloted I would say that the majority are right handed. Chris - Marine Pilot

[@ChrisFrameOfficial]

This is brilliant - thank you!

[@welshpete12]

On yachts we call it paddle affect , same thing only different ! :-)

[@PotatoesAssistant]

Same thing only different?

[@shipmanasmilos]

This exact phenomenon has happened to my single two blade right hand propeller rc boat

[@leardvr]

In aviation we call these forces accelerated slip stream and p factor. I hadn't ever thought about it in ships.

[@andrin4871]

Wow nice 3D animation!

[@CasualNavigation]

Thanks 4ndr1n

[@ptwohig]

I've always called the three point turn a back and fill.

[@xqiuvmah]

What do you call a ship with dual propellers? I'm not familiar with massive cargo ships, but I know in smaller vessels if you have 2 propellers, they always spin opposite of each other. Would this kind of ship be called ambidextrous?

[@CasualNavigation]

In a way, yes. Each does produce transverse but when running together the effect cancels

[@jetblackjoy]

As a right-handed person, I confirm throwing water on my right buttock is easier

[@bieresnavigationettheories5846]

Very good video ) but what if the boat have two propeller running clockwise and anti-clockwise? That's the case on the boats i am working on )

[@CasualNavigation]

The transverse should cancel when both are running

[@bieresnavigationettheories5846]

@@CasualNavigation So no effect of transverse trust. But we sometimes use one propeller to when the other is not running when we arrive at the port. But I don't think it is the same effect

[@kacmic4187]

Thx i was learning for my motorboat licence test (sternik moyotowodny in polish) and there was question about left and right handed propeller.

[@lord_scrubington]

So is a ship with two contra-rotating props ambidextrous?

[@ZeroBlackfire]

What if a ship has a 2 prop system, 1 spinning clockwise, and one spinning counter clockwise? (if that even exists)

[@capnbilll2913]

Yes twin engine ships are common. And give you another option for tight turns by reversing one engine.

[@IcheeCOTC]

yet another reason for stern propellers. if the propeller were at the bow, the transverse thrust would occur when running ahead and force the rudder to be turned one way or another, leading to yet more inefficiencies.

[@paulgemperlein626]

Are there not left handed fixed pitch propellers?

[@CasualNavigation]

Yes. They just act in the opposite direction to the one I demonstrated

[@paulgemperlein626]

@@CasualNavigation Ok, wasn't sure if they were avoided or less common for some reason

[@borysnijinski331]

Left handed vs right handed is better explained by curling fingers on one hand in direction of rotation and looking at where thumb points. For a right handed ship, clockwise rotation means forward motion...curl fingers on right hand in direction of rotation and thumb points forward. In reverse, prop spins counterclockwise and curling fingers in ccw rotation results in thumb pointing in reverse. Use left hand for left handed ships.