Naval Engineering - Ships and their Waves, Turns and Tricks
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- Опубликовано: 16 июн 2024
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Today we take a look at some of the characteristics of ships as they make their way through the water, with some unexpected results!
00:00:00 - Intro
00:01:55 - Naval Engineering
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The bit on guessing speed on the bow wave hight reminds me of a story from WW2. An Italian submarine commander saw an American PC and mistook it for a destroyer, honest mistake. As a destroyer is about twice the length of a PC he also misjudged its speed, and distance to target. Dispite his mistakes he torpedoed and sank the patrol craft. His reward for sinking an enemy warship was to narrowly avoid a court martial for falsely reporting an enemy destroyer sunk.
That should be filed under "Sinking shops need to obfuscate". Under genus : politics. With the best ships in the med, almost all the idiotic losses by Italians falls under "We were so escared!" Creating a power structure where Admirals were more afraid of their country's political idiocrasy than the enemy, have well foreseen consequences. The way the British dealt with such things, after the initial WWI ridiculousness, was exemplary. Nothing is gained by attacking the judgments of a commander of a fleet by telling him what he should have done after the disaster occurred. Only sensible nations understand that. Losing a battleship made Hitler despair, Churchill angry, and Roosevelt unaffected. But it made Mussolini apoplectic. A nation with perhaps the most fantastically powerful metallurgical manufacturing base, who make the most amazing machinery in the world, and the most amazing fabricating machinery to this very day (and ships are fabricated beyond all else) was destroyed by the idiots in power. So was France. They had the very best ships in the world, but idiots commanding them. Because of politics.
The Brits never had the best ships. And some scummy commanders. But they had some genius commanders. And after Coronel, they learnt to butt out. Put the man in charge, then shut the he !! up. Adm. Cunningham is the best example. He made so many decisions made against what he knew his superiors to wish, but he had Craddock on his side. Craddock died to prove micro-management doesn't ever work. And Cunningham let his freak flag fly! He was always on top of things, so much so that made the Italians, a very formidable enemy in 1939, into ridiculousness.
If the Italians became the Chicken of the Sea, Cunningham, and Mussolini had a great hand in it.
Funny thing on turning. Driving an old Coast Guard 44 foot lifeboat (displacement hull) I found that I would turn the wheel, wait a bit, and then the boat would begin turning, which was the cue to start bringing the wheel back to midships so she would set on the desired course. Going up the channel in Saginaw Bay the wind and waves were on the starboard bow. It was turn the wheel, wait a couple of beats, and then bring it back to midships. The bow would turn starboard slightly, a wave would hit the bow, and the boat would settle into a straight course down the channel again. Repeat. Once the rhythm was found the boat would stay right in the center of the channel according to the chart plotter.
Is that kinda like drifting a boat back and forth?
Not, exactly displacement hulls that really aren’t all that fast compared to their planning counterparts, so the water moving over the rudder(s) is moving slower, so exerting less steering force for a given size of rudder.
Add the effect of swells in the hull which will try to push her around a bit, you have to anticipate what the next wave is going to do to the boat, and correct ahead of time, otherwise you’re going to be making basically a zigzagging course. Keep in mind also that larger rudder angles rob you of speed as well thereby make the rudder less effective when you want to put it in the other direction to stop the turn.
In a head or beam sea (swells coming towards the front or side of the vessel) it’s not too bad in most normal conditions. In a following sea, the swells can often start to push the stern around and you’re going to have to be fighting yawing, big broad transoms are pretty good for doing this. Anecdotally, I was the skipper of one boat that in a following sea, I can only liken her handling to that of a garbage truck, being driven down hill, backwards, on ice and with a flat tire.
Wonder if they use the same technique coming into Maumee bay. The channel and angle relative to the prevailing winds is very similar.
Drach takes on his most dangerous challenge yet... Making people enjoy science using boates
As a submariner I can tell you all the captain's used to use the length of stern wash as it was more predominant with the low height of the periscope
That was brilliantly explained, with not too much maths or formulae.
What I’ve always found remarkable about bow waves is the angle of the bow wave relative to the direction of travel. It doesn’t matter if it’s a battleship, a speedboat, or a duck, the bow wave will always be 19.5⁰ regardless of speed, displacement, or bow shape. The bow wave angle is set by the properties of the fluid and not the properties of the vessel passing through it.
(Welcome to Weird Wave Fact Friday 😂)
Technically, wouldn't it vary a _bit_ depending on the temperature and salinity of the water?
@@vikkimcdonough6153 ...I'm no expert, but by my understanding, _theoretically yes,_ but I would not be surprised if the difference is MUCH less than half a degree for almost the entire range between freezing and boiling...
@@vikkimcdonough6153 As those are properties of the fluid, yes.
Another interesting thing that happens when starting a turn is that the ship will first list into the turn due to the moment of the rudder drag. After the ships starts to turn the centrifugal force takes over.
The center of gravity being high so the list will change to the outside of the turn.
Not technically the drag from the rudder, rather the hydrodynamic lift that the rudder generates, but yes. (Note that the lift here is lift in the sense that the rudder is acting like an airfoil. The force is sideways towards the outside of the turn, not up)
Your description of 'kick' is fascinating. As someone who cox'd a sailing club rescue boat (13 foot Dory with a 30hp Mercury on the back) for several years, the fact that the back would 'step out' as I applied power whilst steering into the turn comes as no surprise. I suppose a great way to describe it to land based folk would be when you are driving a rear wheel drive car vigourously down a country road and you turn into a corner and the vehicle slides out before straightening up. At least that's what it feels like - though it is amplified on the water.
My analogy is that it's akin to drifting in a car. It's not entirely accurate, but for the initial phase it applies.
I believe that the "stepping out" you discuss is a separate phenomenon; that's due to the pivot point of the boat being forward of the stern. The "kick" is the _entire ship_ being moved sideways opposite the direction of the rudder (not a turn, as stated in the video).
The book makes this clear. The exact quote from Knight (15th ed., p.218) is (emphasis mine) is, " _f. Kick_ The distance the ship moves _sidewise_ from the original course away from the direction of the turn after the rudder is first put over."
@@Curt_Sampson I think you're correct about the "stepping out" being a different situation. I remember many times when sailing (12.5-foot centerboard dinghy) when I'd have to use that principle to wiggle my way around an upwind mark when I couldn't quite make the layline. First throw the helm to leeward to point the bow above the mark, then back to windward to rotate the stern clear of the mark as the remaining momentum carries the boat around it.
Remembering an earlier Drachinfel video. Concerning the ships steering kick.
Drach showed a picture and mentioned the USS Enterprise helmsman Tokyo Drifting the ship during an attack.
Do you know which one? I don't recall this one.
@@CiaranMaxwell No... I don't. It could be about 6 - 8 months back --- maybe
@@RectalRooter Thank you.
Unrelated, but I just saw your name, and it reminded me of a Futurama gag. "Call Robo Rooter when you flush your towel; we can also help with an impacted bowel."
@@CiaranMaxwell haha I don't member that Futurama episode off hand. Maybe it was inspired from the same company The Roto-Rooter jingle
@@RectalRooter Oh, I'm certain it was the same inspiration.
The gag was one of their one-off ones. Thompson's Teeth was another one: The only teeth strong enough to eat other teeth.
Drach,
Great video, it brought back a lot of memories from my day as a US Navy Officer of the Deck (OOD) underway. Here is my two cents worth:
Let's assume a starboard turn. When the rudder is put over to starboard it develops a horizontal lift force to port, typically below the ship's center of gravity (G). Initially the ship is still translating forward, so we have the following effects occurring simultaneously:
1. A translational motion to port as illustrated in the diagrams
2. A heeling moment to starboard, i.e., towards the direction of turn (in this case to starboard)
3. A rotational moment to starboard about a vertical axis through G, causing the drift angle (similar to a wing's angle of attack) to increase from zero to some positive angle
The ship's hull is essentially a huge inefficient symmetrical airfoil; its effective area is essentially length X draft, and it acts at about half draft. As the drift angle increases from zero it develops a huge horizontal force (more than the opposing rudder force) directed towards the center of the turn. From basic physics we know that a force at a right angle to velocity causes circular motion, and this is why the ship changes heading in the turn. In addition, the hull's side force overcomes the rudder side force and causes the ship to heel towards the outside of a turn. At this point the rudder angle is essentially controlling the drift angle.
An experience mariner instinctively knows this sequence of events during a ship's turn, and he can tell which direction a ship is turning regardless of his location in the ship.
The bow doesn’t really point to port when turning starboard and vice versa. What happens is that the entire ship moves sideways, although the stern moves further than the bow. What is essentially happening is that the rudder turns the ship to starboard by adding a net force at the stern which points to port. This force causes a moment about the ship’s center of gravity which moves the stern to port, pointing the bow to starboard. But because it is a force, not a pure moment, it both rotates the ship and also moves the ship horizontally, to port. What makes the ship turn to starboard is that once it rotates, it’s basically skidding through the water (kind of like a sports car drifting around a corner.) This causes the hull itself to act like a giant airfoil, generating a force which points inward, thus moving the ship to starboard.
As you were describing “Kick” my mind went to a famous collision in Halifax between the Mont Blanc and the Imo.
Naval Architects never get enough love... I know titles change over the years and it's all engineering but manoeuvring and resistance has normally been the naval architects domain with the occasional person being called a hydrodynamisist.
The kick is similar to how you turn away from the corner on a motorcycle to turn in and turn in to turn out. If you imagine a line going vertical from the back as you throw the rudder it pushes the bottom of the boat away from the line causing a rolling moment the wrong way until the pressure on the front rolls the boat onto outer side then the inertia is cancelled and the turn line is made. It's basically evolving an aero form with rolling moment giving longer and or shorter lines depending on whether it takes the outside of the hull or inside respectively.
18:55 Related concepts are Advance (forward distance made between the time that the rudder is put over and the time the ship is steady on her new course) and Transfer (horizontal distance over the same period of time).
The "kick" of the rudder leads to the classic rookie mistake moving a boat away from alongside a jetty. The beginner selects forward gear, turns the rudder (or the outboard motor) and instead of moving away the boat jams itself hard against the jetty.
I learned this lesson the hard way as a stupid eighteen year old in a 28 foot Chris Craft Catalina. 😬
I'd never thought about the dynamics of turning a vessel with a rudder, and I now have a feeling the kick effect was responsible for the complete dog's dinner I made of my one attempt to steer a narrowboat. That or the canalside pub we'd stopped at for lunch, anyway...
19:42 " _Turn to page two hundred and ninety four_ " Drach said coldly
It's on page 190 & 191 in my twelfth edition
the kick was the reason for the sinking of "Costa Concordia" ... the captain ordered hard to starboard way too close to the rocks, thus sending the ship right into them. Bravo for your clear explanation. This captain, Captain Francesco Schettino, in prison for the murder of the 32 deaths, might want to subscribe to your channel. He booked a room in a local hotel while his boat was sinking and people aboard were being rescued by the coast guard.
ships and boats turn around the meta center, Drift by wind, current, steering heading. speed all change and must be accounted for safe ship handling.
Hmm . . . The turning response is one possible reason that RMS Titanic hit the iceberg. The initial response, moved the ship closer to it, before the actual turning took effect.
The question that comes to my mind is, can you use this behaviour to sot of "jump sideways" in a ship, using consecutive opposite turns of the wheel?
The issue with the Titanic's turn is more so that the most effective position for the rudder - i.e. right at the stern of the ship - means that ships will turn by swinging their stern in the direction of the rudder travel. It's a bit more complicated than that, but essentially when Titanic's turn began, her bow initially carried on in a straight line whilst her stern moved closer to the iceberg. This had the disastrous effect of running her side along the berg, and from there history takes over.
As a ship’s officer of 24 years experience, it has never been my experience to see the vessel’s head turn opposite the rudder’s command at the start of a turn. A merchant vessel will typically move bodily away from the direction of the turn, feeling the “kick”. Kick is also used to describe giving more engine speed during the course of making a turn to bring the vessel’s head around faster.
He did mention this was for stern only rudders.
@@kennkoala just wanted to relay my experience. I haven’t operated a vessel with a forward rudder. That’s a rare bird…
I think he was incorrect to use the word "turn" at 20:54; the ship actually _slips_ sideways, as I mention in another top-level comment on this thread.
The exact quote from Knight (15th ed., p.218) is (emphasis mine) is, " _f. Kick_ The distance the ship moves _sidewise_ from the original course away from the direction of the turn after the rudder is first put over.
Looking at the diagram in the video, I think that the BOW probably goes straight ahead, eventually turning to starboard as the stern kicks to port, but that the stern (because of the push from the rudder) moves to port. This will make the center of mass of the ship shift left before it shifts right, as the diagram shows. The diagram (as drawn) doesn't really show the position of the bow in the turn, so I agree with you. It's a bit deceptive (not intentionally) as it's drawn.
"A ... vessel will typically move bodily away from the direction of the turn"
I could be wrong, but I think this is what he was trying to describe. I don't think he was saying the vessel’s head would turn opposite the rudder’s command, but I did find his wording a bit confusing on this point.
Very nice video
I'm currently studying this very subjects at university
And you did a good job at explaining in a simple and intuitive way
Kick sounds like adverse yaw in an airplane aerodynamics, when the plane initially (and briefly) turns the other way when starting to turn.
I was just wondering if there was an aeronautical equivilent!
@@bartsanders1553 if you want a great in depth explanation of adverse yaw, look up the channel “Greg’s Airplanes and Automobiles” and watch his videos on the Wright Brothers.
@@bartsanders1553well, from a physics standpoint both gases and fluids are fluids, so that makes sense.
@@urishima Intuitively at least
Fascinating - I've just finished reading From Warrior to Drednaught - it repeatedly mentions Froude's work - It's astonishing how our forefathers got to grips with all this theory
On the turn, reminds me of the wonderful scene in Father Goose where the Australian gunboat executes a hard to port turn from a standing start...
I was going to ask you about this in regards to Hood and the impact of her turn on the wave trough. Quite excited to hear about this.
Drach already covered that in previous dedicated video.
@@titanscerw I'm actually not sure he did. There's quite a bit of discussion about the trough being there, which it clearly is. But what does a turn do to it?
As far as I'm aware there's one photograph of Hood post '31 (iirc) refit in a turn at speed that seemingly shows the trough increasing inside the turn. Obviously the photograph doesn't show outside the turn.
But if the trough is increasing on the inside of the turn, would it increase on the outside as well? IDK
@@PaulfromChicago the key is the timing, my conclusion is she was hit right at the very start of turning, before the rudder had even fully gone over, which would mean she was either still going in a straight line or in the middle of that little shimmy in the opposite direction. Which, given the overall aim was a turn to port, would've nudged her bow out to starboard with the accompanying small roll to port, which would've exposed her side even more for a handful of seconds.
@@Drachinifel I agree, that seems a very reasonable explanation. I think that when the shell came in, the trough was definitely doing something related to the turn. (Heck, I think at 20 plus knots the trough was probably bad enough in its normal state to be a reasonable explanation of what happened.)
The question I have is the photograph shows the inside of the turn and the trough clearly deepened in that turn. But on the outside of the turn, which I think is what Bismarck would see (as I understand that would put Hood onto the same tack as Bismarck), does the trough increase or decrease there?
@@PaulfromChicago the trough would not in itself change all that much, but the apparent depth would due to the roll/lean of the ship and potential calm spots being caused where the ships water shadow caused a calm area in which the bow wave and trough would be the only waves present. The wavelength would also change as the ship lost speed. A high speed and sharp turn might also cause a small degree of water displacement on the outside and void on the inside, which would exacerbate apparent decreases and increases respectively.
I watch Drach's channel all the time, and youtube has decided for me that I shouldn't. Can't remember the last time I was notified of a new post
Edit: yes, I tried to change the settings, then change them back. Even tried unsubscribing and resubscribing.
Did you tell YT to notify of All, Personalized or None?
@RonJohn63 all, and yet haven't gotten a notification in months. I even tried to unsubscribe and resub, but it didn't work. I know when Drach drops videos, so I just keep my eye on the channel.
@@fullsalvo2483 that's puzzling/interesting.
That sucks man, I've had a similar thing with a city skylines channel. Like you, I know when he drops so I just look, but it's annoying
All hail the algorithm.
Hi Drach! Love the engineering design videos whenever you do them! Something that might have been helpful, if you plan on doing something like this again, is having the equations on screen, and have the pictures annotated where the peaks and troughs are.
I really love your short tutorials. Whether I learn something new (often the case), or confirm something I thought I knew, I learn. Thanks
The destroyer slicing through the sea at 3-30 or so is HMS Petard (As in "Hoist by his own").Her class was an oddity among RN WW2 Emergency Program DD's as she mounted five 4 inch AA guns - P Mount replacing the after quad torpedo mount - rather than four 4.7 inch low angle guns or four 4.5 inch DP guns. Later, the four surviving (one was later sunk) vessels had that gun removed in favor of the fish.
Excellent, more engineering.
Yep
These are my favorite types of videos. I learn so much that I'd never considered before👍
Just wanted to let you know that you do the best sponsorship segments I've seen on RUclips
Drach,
please do a session to explain "squat" in shallow waters
cheers
Robbo
I very much enjoy this series. It’s difficult to learn the basics of this sort of stuff without getting your hands on some hefty books, otherwise
Absolutely fantastic content Drach - thank you
My only interest in maritime matters used to be small sailing boats, but this channel, and your enthusiastic narration and dry sense of humour have me hooked ! Many thanks, and keep the videos coming !
I always love your engineering videos, they probably take a lot of work, but they're always interesting and worthy of watching multiple times.
Fascinating stuff! I have seen a colour photograph of HMS Hood at speed which clearly shows her hydrodynamic characteristics. Her most prominent trough is clearly below the armour belt right where the 4" magazine is located. Having seen a documentary showing that the 4" magazine was the site of the explosion which destroyed her I think I managed to add 2+2 and went Ah!
Love these engineering videos. Great to get a true engineers perspective on it!
While in the service, we used to run man-overboard drills. A dummy was thrown in the water and the ship turned to come back to the dummy's position. The rudder was always turned to the side where the dummy was thrown, then the rudder reversed to loop back. I was told this was to keep the screws away from the dummy/person in the water. Basically "kicking" the stern around away from the person/dummy. Our ship had twin screws and twin rudders. Very maneuverable. This video's explanation enhances my earlier intuition. I love the diagrams. While watching these videos, fond memories come about . I wish I could smell salt water while watching ... maybe AI in the future can help us :)
It's sometimes called a Williamson's Turn; the intent is (1) as you said to keep propellors clear of person in water, but also (2) so that you come about and run back down exactly on top of your own course. Thus increasing chance to see the MOB.
Yep. When I qualified on the helm of the Sumner class, Zellars DD 777, the turn towards the MOB was what I was taught. We then ended up steering a figure eight to bring us back to the MOB.
I've heard that people are working on something like "smell-o-vision," but it's still not going to happen for quite some time.
That is the type of subject I really like. Thanks.
Good work. I'd like to know more about:
-- what's the turning radius at full rudder, and how it varies with speed
-- the amount of speed lost in a turn
-- the amount a ship leans during a turn.
I'd be happy with one typical example. Of course these numbers will vary depending on rudder size, metacentric height etc.
The Casual Navigation channel on YT is full of videos on similar topics to this presentation. Well worth checking out that channel.
yes, I watch that one as well
Gives a whole new dimension to Scheer's "Battle turn away to starboard"
I’m really digging these videos. I’d never heard of drift before
As always great information Drach!!!
Excellent! If you have ever driven a forklift. The rear placed wheels approximate the ‘kick’ of a ships stern mounted rudder. Also a ships waves are better shown in a motion picture as the sea’s own waves effect the crest & trough caused by the bow.
WOW! This video was interesting and enlightening to the nth degree. I was fascinated. Been watching you for a while now, and enjoy most of what I see. I rarely comment on the videos I watch - it takes something special to move me to take the time and effort to get to the computer to do so (usually watching on a big TV). This one was great! Thanks so much! I do have a question you might be able to answer - When out on small boats moving fast and you turn the steering wheel hard over, the boat will lean into the turn. For example, you turn left, and the boat will "list" to the left as you execute the turn. However, in photos of aircraft carriers (or any large ship) in a hard turn, the ship actually leans the other way, toward the outside of the turn. Could you do a segment of a video that explains why this happens and at what ship size the change from leaning toward the inside to leaning to the outside happens? Thanks again for all the great content!
Brilliant format Drach
Informative and entertaining. Thanks Drach. 👍
If your still working to demonstrate face hardened armor on the small scale, one thing that springs to mind as a stand in for the hardened face would be a pane of glass. If you have a glazier nearby you can likely get all the scraps you need for free, and of varying thicknesses too. Also if the air rifle your using is a .177 caliber you should be able to shoot steel BBs along with lead pellets. This might help demonstrate the differences between shell types, HC vs AP etc. Alternatively, a laminate target that might work as well is thin mild steel (bean tin or the like) on top of plywood, or aluminum over HDPE plastic. And a neat little trick to get BBs to work in air rifles that were not specifically made to use them is to stick a tiny bit of tape (scotch, masking, packing, etc) on them to increase the diameter just enough to prevent the BB from rolling out the barrel.
Probably also worth taking a look at the "Archery vs Armor" series by Tod's Workshop - now up to 8? videos with lots of great demos - for ideas on how to put together demos. Among other things, they look at face hardening of arrows and try them versus different types of steel, which probably has some amount of overlap with naval shells hitting hardened naval armor.
Well, he did use glass in his first demo. I keep thinking he could get C&Rsenal to help again...
Two things I have observed related to this wave propagation behind a vessel are that after watching tugs on the Ohio river pushing large tows up river during lower water levels, I was surprised to see huge single waves suddenly rise up out of the calm river long after the tug had passed from the propwash interactions with the bottom. they were close to 1/8th mile behind them or more, and unpredictable. They were white capped and rolling waves traveling down river with a suck hole in front of them! No place for a small boat! Do not follow directly behind tugs even within a 1/4 mile. Another effect was related to me by my father about a stern wheel paddle boat on a lake. I was taking my 14' aluminum boat to lake Schaffer in Indiana. There's a paddle boat that operates out of Indiana beach called the Schaffer Queen. He said to me, "dont follow that boat! They set up rolling waves behind them that look small, but if you get trapped in them, the suction from them will almost swamp you, and it's very hard to get out of!" He had learned this the hard way! He said that it was the most afraid he'd ever been in a boat, and they were over 100 yards behind it! That was behind the "Dixie" in North Webster in a john boat.
Always the enlightened discussion Sir…Darach..😎
As usual, photo selection is excellent.
Extremely interesting. Keep'em comin' !
Great video, Drach! Absolutely fascinating. Now I understand why Navy guys get such a kick out of turning. (Que snare drum and cymbal's.)
Fascinating stuff as always!
Eloquent, well spoken, precise. ..Subscribed + !
Honestly, one thing I'd be curious about which would make a decent related video would be the history of how these equations were made/how naval engineers developed hull forms for different ships. Like, I seem to recall there having been controversy in the USN about the adoption of water tank testing of scale models, for example.
Agreed. There is an interesting history book along these lines for aeronautical engineering: "A History of Aerodynamics' by Anderson, by I don't think anybody has done anything remotely as good for nautical engineering.
I love it when people can explain complex stuff in simple ways that build intuition!
Wonderful vid sir - love the math, I had no idea of either of those topics and they super interesting. And agree, that shot of the USS Illinois hammering it is pretty darn spectacular.
Although beyond the scope of this channel, the interesting hydrodynamic phenomena utilized in navigating the Houston Ship Channel known colloquially as “Texas Chicken” makes for an interesting read.
He basically described how to play "texas chicken" towards the end.
Great stuff as always. Thanks
Thanks Drach.
Cool! Thanks Drach!
Water is weird stuff scientifically, so it's not that surprising that interactions with it are equally not straightforward either. I had heard about the "initial" part of a turn elsewhere but not the maths that go with that - so thank you for that explanation Drac
As a 'chemist' I used tto write in my notes, HOH, instead of H2O.
Done to remind myself of the Unique chemistry of water.
The melting point of methane, which has the Same molecular weight as water is -162° C...as opposed to 0°C
@@philgiglio7922 Water is a very strange thing, there are actually very few compounds that expand when freezing. Plutonium being another, but few have hands-on experience with that..
@@jbepsilon Which is probably a good thing, all things considered.
The section on how a ship actually moves when you apply rudder reminds me of how motorcycles turn when steering input is given. Physics is a counter-intuitive beast.
This is very interesting information! Please have more of this type of information. Thank you very much.
Every time I hear the new theme, all that runs through my head is Night Ranger. Understanding and anticipating how a DDE would kick between tactical and final, AWA knowing where the pivot point was, saved my bacon several times while conning during RASOPS, doing emergency break-aways, AWA bringing her alongside. As Les Grossman would say, "It's physics"! Also, though the big girls never required the skill, any RCN reserve officers of my vintage can explain how to use the 'paddle-wheel effect' to manouver a single screw vessel just like our grandparents did in the Flowers during the war. We always had to of course, incude the turrning circle into our wheel-over calculations for pilotage nav plans as you rightly noted. Out fenders and carry on, Drach!
Watching the last few minutes would have helped considerably when we hired a narrowboat several years ago. Many days of trial and error allowed me to time turns, but I might have saved a few brushes with weeds and a couple of bumps going under bridges.
Very interesting episode! Thanks
cheers D enjoyed that
Thanks, Drach!
This was really interesting about the "kick" when turning. Sadly, the Dali, which crashed into the Francis Scott Key Bridge in Baltimore a few days ago, seemed to drift veer toward the bridge support after they put in hard rudder to steer the other away.
Great video
Thanks for the lesson.
Thanks Drach
I have sometimes wondered how much 'kick' may have had to do with the Titanic collision.
Very interesting. Thank you
Fascinating 👍
Clay. You can use 1" thick clay as homogenous and then use a torch to face harden it.
In the days when canal boats were pulled by horses, the horse worked hard accelerating the boat until it 'got over the hump' of its bow wave. The horse then had a much easier time of it.
I worked WPC fast craft for years mostly on Incat 74(Seacat Scotland, IOM, Hoverspeed Great Britain, France) and Incat 81(Seacat Rapide) and something that used to catch a lot of craft around us out was from the front we're going much faster than we look because WPC = Wave Piercing Catamaran. Our bow wake always looked quite calm.
We were still a fast craft though so all the fuss and drama was out the back! Instead of a traditional screw & rudder set up, we had what basically amounted to what would happen if you take a jet ski and make it massive...then strap 4 of them(2 per hull) to the back of a ROPAX. The result is a massive rooster tail wash out the back practically the height of the ship.
Yachtists were ALWAYS underestimating just how fast we were going heading at them and get a hell of a shock when our actual wash is a little more than they were expecting 😂
This very much reminds me of my Fluid Dynamics 1 course at university.
Very interesting discussion. I'm an oceanographer (among other things), and one of the things I learned when I was an oceanography student is that wave speed in deep water (shallow water messes things up) is determined by wavelength of the wave and can be calculated as C = square root of (gL/2π), where C = wave speed in m/s, g = acceleration of gravity in m/s2, and L = wavelength in m. It works out to about 1.25 x sq. rt. of L (measured in m/s and m).
As a sailor a long time ago, I always wondered why the hull speed of displacement vessels was proportional to the square root of the wavelength, and when I learned about the relationship between wave speed and wavelength, I always suspected that it was because of this relationship.
When I saw your description of the Hood photo, I took half the waterline length (430 ft), converted to meters, and inserted it into the wavelength equation, got the speed, converted to knots, and got 27.81 kts. When I heard you say that the wavelength of the wave was between 400 and 420 ft, (14:16) I converted 410 ft to m, stuck THAT into the wavelength equation, and came up with 27.16 kts, squarely within the 27-27.5 kt speed you calculated using your calculation. I did this BEFORE listening to your report of the estimated speed. Interesting. To me that means that hull speed is a resonant speed with a wave the length of the ship. Any faster, and it makes the hull move faster than the wave, needing a lot more energy to do that.
Drach's ships do tricks and turns, whilst a brothel ship is turning tricks.
Thanks! That was interesting.
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Hey Drach, glad the book is going to good use. Couldn't be happier seeing it used in a video.
This shot of Hood at 15:04 I'm guessing shows her a bit faster than the previous one 14:45 , (28knts) .. or upon further review as noted it's harder to gauge troughs/valleys... maybe there's another valley along the forecastle, so she's plowing along in heavy seas around 15 knts. A Beautiful sight.😊
Very interesting
More like this!!! 😁
Funnest. Friday. Ever.
I'm not that great with math equations, generally speaking, but I do have a fascination with calculating the speed of vehicles for various reasons/situations, so this video was very interesting to me. I can't say how often the info will come into effect for practical applications as I don't spend a lot of time on or observing boats/ships, but as the saying goes, "better to have and not need, (the information for calculating ship's speed, in this case,) than to need and not have."
Good one
I knew Drac was bring maths into this.
Turning - I always worked on the basis of (Rudder) Apply, Catch, Ease, Steady - then you have the steady turn. There's an art of course in being OOW conning the ship and allowing for the delays in actually executing the order. And if you want to know how it works, go drive an older LandRover type vehicle in a slalom ! You have to use exactly the same principles.
If one wants to learn how to steer a vessel, go to the grocery store, get a grocery cart and handle it from the front. The front has the steering wheels, so to turn right, the back will kick left before actually turning to the right. This feature gets more recreational boaters in trouble as they think a boat steers like a car.
On various boat trips and watching ships on the movies and elsewhere I had unconsciously noticed that kick business - didn't know it was a thing though.
I love your videos! One thing you should try to add is the name of the ship that you’re showing in the pictures. I often see a very interesting ship and would love to learn more info but without the name I’m stuck. Thanks for all the great entertainment!
For those who are interested, the concept of constructive and destructive interference described here is not just limited to understanding the interaction of ocean waves with ships: it's fundamental to a number of technology areas ranging from phased array radars to sonar arrays to medical ultrasound. Using an array of emitters with strict control over timing allows one to place the interference in space, and hence effectively 'steer' the beam very rapidly: wikipedia has some nice animated demos. Some of the early work in this area was done in 1905 by Karl Braun, and the Germans deployed some land-based MAMMUT Phased Array Radar systems as part of Fortress Europe to detect ships carrying an invasion force during WW2 (described in a paper in the 2019 International Radar Conference, IEEE, Hugh Griffiths).
I'm not sure whether any phased array systems would be deployed on warships until long after the period covered by the channel (feel free to correct me if I'm wrong!).
It's interesting that in some ways the Germans were well ahead of the Allies with respect to radar: any non-trivial surface warship today probably carries a phased array radar for close in defense systems if nothing else, and while the Germans didn't put those on ships, they were the first to build and use that type of radar for real applications (as far as I know).
In other ways, of course, they were far behind.
On putting the helm over the bow does not turn in the opposite direction, the stern will swing to the outside of the turn, the bow swings in the same direction as the helm but, the center of mass of the vessel will drift in the opposite direction of the turn initially before steadying into the turn. I spent 40 years at sea, retiring as a captain 16years ago. And yes I do enjoy retirement.