Naval Engineering - Ships and their Waves, Turns and Tricks

[Music] hello everybody and welcome to this video which is kind sponsored by Squarespace So today we're going to be creating an article from scratch the Admiral y Moto one you saw I created using an existing template that was there when I created the article page this time I've just gone and added a brand new one copied in the text from actually that's the script for this particular video given it a quick title and then I've decided oh actually you know what I want to put some pictures in this one you know embedded in the text as you can see each paragraph already has these nice little splits so I can just hit plus and select image and it puts an image Block in for me it doesn't require me to put an image in immediately so I can decide how many images I want and how the whole thing's going to look before I have to start uploading things but then once I've done that then it's a case of just hitting upload from file selecting the appropriate images and letting them all upload nice and quickly so obviously in this case we're looking at various ships and their profiles and one or two diagrams as well and just like that the article's done so then I just have to go and hit save although go into settings first choose a cover image for the main page hit save and just like that a brand new article is ready for the website nice quick easy simple so if after all these little mini tutorials I've been doing you think you could build a website for maybe ideally Naval History purposes but you never know you might want to do it for some other reason then head over to squarespace.com trenell you can get a free trial and once you're ready that little link will give you 10% off your first website or domain so thanks once again to Squarespace for sponsoring the video add on with the main show so whilst I'm still working out how to demonstrate the differences in choice between having Face hardened and homogeneous armor plate on your gun turret's roofs using an air rifle different Metals in the pallets and various materials I can get from the local hardware store I thought we'd continue our occasional looks into Naval engineering by reviewing some other essential features of ships to help everyone understand how ships behave a little bit better this will also reveal a small but interesting detail about how ships turn but primarily the point is to give you a neat little trick to work out how fast a ship is moving based purely on a photograph now before we continue I should mention the formulas and diagrams that you'll see that underpin this video are taken from two Publications one of which is Knight's modern seamanship a tried and tested publication that's about as close to a Bible for Sailors as it's possible to get in the Realms of ship handling first published in 1901 it's still available in its 18th Edition although the one I'm using is an 11th Edition from 1945 as that sits nicely in the Channel's time period the other is fundamentals of construction and stability of naval ships which at least was possibly still is an essential textbook at the US Naval Academy so firstly we're going to discuss bow waves and speed it goes without saying that a ship in water is obviously displacing a certain amount of water from where that water would otherwise be which is why a ship's mass is registered as its displacement and however when a ship starts moving through the water it's obviously displacing previously undisturbed water ahead of it whilst other water moves in behind it to fill in the void that's left by the passing of the ship now to move all this water around requires energy obviously the ship has to push the water aside to pass through in the first place and the more water that has to be moved aside in a given amount of time the more energy you need hence why you need more power in your boilers to go faster and why a slim bow is better than a blunt one one of the features that this causes is a bow wave which at any appreciable speed will be quite visible and indeed methods of Faking or disguising a bow wave to give a false impression of how fast a ship is actually going was one of the key concepts of Warship camouflage in World War I and World War II the more energy that is put into displacing water the higher this wave will go so as a general rule the faster the ship moves the larger the bow wave although you can get some pry impressive bow waves at low speeds if you are moving a ship that has a fairly Bluff bow simply because the greater immediate frontal area of the ship means that more water has to be moved very quickly which of course then needs more energy but the energy that creates the bow wave doesn't just vanish when the white spray falls back into the ocean that spray is really actually only a small part of the total water displacement that's going on the wave created is a wave in the true sense of physics as well as in the more colloquial sense and as such it will continue to oscillate in the manner of a sine wave for some time until the energy in it has been dissipated now this energy will spread from the ship in the form of the ship's wash but it also runs along the ship in a series of waves and troughs or Peaks and troughs crests and troughs there are various terms for it of gradually decreasing magnitud ude each cycle of which also sends out its own Peak and trough in the ship's wash hence why if you're moured on a river and a ship passes by a little bit too fast or a little bit close the ship or boat that you're on will rock back and forth multiple times as each successive Peak and trough hits you whereas if the bow wave energy just magically vanished after the initial bow wave itself you just feel the one hit you can see this from top down photos quite often U the multiple waves coming off the side of the ship now as the ship's speed increases not only does the starting amplitude or height of the wave increase due to the a mentioned greater energy that's going into it but with an increase in speed the length of the wave that you see also increases and that's perceived by the distance between the Peaks and the troughs going down the ship's side now these two functions wavelength and amplitude are independent of each other because as many previously you could be towing a barge at let's say four knots and thus have a very short wavelength but a very high amplitude because of the slab front of the barge or you could be moving a battle cruiser through the water 18 knots and have a fairly long wavelength but you could have a similar height or even smaller amplitude to the waves depending on exactly how Sleek your bow is now there are some things that can affect the overall features of a bow Wave A bulb bow either intentionally installed or unintentionally in the case of some early Ram bows can decrease the amplitude of a wave as a whole the waves of the sea can also amplify or reduce the amplitude in certain circumstances this is because of what's known as constructive and destructive interference essentially if two waves in any sort of medium whether that being water light waves radio waves Etc overlap then if the Peaks and the troughs of the two waves align they are said to be in phase and the magnitude of the resulting waveform is increased conversely if they outer phase and the peak of one overlaps the trough of the other and vice versa the resultant waveform is reduced possibly even canceled out entirely if the two waves are of very similar power of course this relies on the wavelength being similar for both waves so in any given sea State you might have mitigation or enhancement of a ship's bow wave form as it travels at one speed but that same sea State might have a different much lesser effect if the ship is traveling significantly faster or significantly slower this is actually the exact principle on which bulbus bows work by generating a wave ahead of the ship that's 180° out of phase with the actual bow wave that the main hole generates which obviously means this is for a given speed regimen it means that the ship can Cruise more efficiently at or around that speed need by minimizing the wave profile down the side of the ship due to destructive interference because a very high wave profile otherwise causes drag amongst other things now when the wavelengths are very out of step with each other let's say the ship's moving quite fast but the sea State waves are quite short then this can result in slightly irregular behavior of the stronger wave but the effect depends on the amplitude and and obviously therefore the energy of the two waves in question a series of short wavelength SE waves with Peaks let's say a foot high are going to have a very little visible effect on a bow wave that's cresting at about 10 ft to start with but a ship that's moving slower and therefore with a shorter wavelength might find a twoot bow wave form completely obliterated from view if it happens to be moving through Seas with 20ft waves but fortunately for us the former situation where the ship's bow wave overcomes the local sea state for all intents and purposes is much more common than the latter now completely incidental to all this this entire principle of the bow wave and it's formed down the hole is the main thing behind the idea of Hull speed which is a matter that we'll talk about in a lot more detail another time but very briefly speaking as a ship approaches a certain speed which is proportional to the whole length then the wavelength of the bow wave becomes so long that it's actually just one long slope from the Crest at the front to a trough that matches the waterline length of the ship I the wavelength is actually twice the length of the ship in question now at that point the ship is essentially constantly trying to move not just forward but also uphill and the energy to do that just goes straight through the roof but as we said we'll discuss that more another time now why apart from establishing that bow waves and their crests and troughs down the side of the ship are in fact a thing which a few people over the years have denied in various comments both here and elsewhere why else is this useful to you well the wavelength of these waves that is the distance between any two crests or troughs has a mathematical formula that's directly related to the speed of the ship that formula is L = 0.5 557 v^ 2 where L is the wavelength measured in feet and V is the ship's absolute velocity measured in knots and for those of you who want to use metric you would have to divide the result by approximately 3.3 to get a wavelength in meters Now using basic mathematics with that original formula we can derive that the square root of the wavelength divided by 0557 is therefore equal to V the speed in knots and that in turn means that if you have a picture of a ship where you can see the Peaks and the troughs of the bow wave and you know the length of the ship in question then you can work out the wavelength and thus calculate the approximate speed of the ship this is a much better approach than looking for the amount of smoke from a ship's funnel or the rate at which that smoke is being swept back because of course a stiff headwind can blow funnel smoke back very sharply even if the ship itself is actually completely anchor and lots of smoke powering up from the funnels just means inefficient combustion which more often than not indicates that the ship might be powering up to move at speed but most of the time is a good indication of the fact it hasn't actually reached top speed yet since photos of ships moving at their top speed especially to be fair when they're oil fired tend to show remarkably little smoke since at that point the boiler temperature and pressure stabilized and most of the fuel is actually being burnt coal powered ships moving at top speed do tend to kick up a bit more smoke um because it's coal amongst other things so let's take a few examples this is a photo of hood on her way to the Battle of Denmark Straight you know a day or two before she fought that battle and some of you may recognize this photo now apart from the rather large trough being present right where I suspect she was hit with which you know is the basis of my theory on how she was destroyed we can also derive her speed in this photo we know that hood was about 860 ft long at the water line and we can see that there are three crests and two troughs that are just about fitting along her length uh you've got the bow Crest itself a second crest that's peaking roughly around about the second funnel and then you can it's building to a Crest again just as you reach towards the stern and then you've got the very obvious trough around about the main M and a slightly less obvious trough because as you can see in this particular F she's just in the process of burying her boughs uh but you can actually see that that trough is about the level with the back of the of B turret or the forward part of the conning Tower the deepest part of that trough now of course you've got the bowel Crest as we said we've got the second crest and that if you scale along with a plan of hood means that the distance between the bow Crest and the funnel Crest is about 400 to 420 ft exactly what figure you're going to get depends really on what part of the funnel you're measuring to and exactly where you take the start of the bow wave Crest but you know it because you're measuring in feet approximations like this are still valid now that tells us using the equation we mentioned earlier that in this photo hood is moving at between 27 and 272 knots so that's useful information now the only problem with this method is that a photo taken at C Level which is usually taken from another ship or even a boat if they're any kind of distance away can slightly obscure the waveform along the hole either because intervening sea waves closer to the camera get in the way or potentially even the rolling wave of the bow wave Crest that's obviously coming away from the ship might also get in the way and obscure things so shots from ahead at very close to sea level are somewhat less useful than shots from alongside or in the air now that's not to say you can't make observations from a photo like this this is a hood on her speed trials early in her career but it is a little bit harder so in this case you can see roughly where the trough is uh because there's no spray coming up from the side of the hle so the the absolute depth of the trough actually in this case would be about a breast the second funnel but because in this case you've actually got the line of advance of the ship's bway in terms of you know the ship's wash coming towards you from a relatively low angle it's difficult to see exactly where that is and you can see where there is a peak coming up just forward of X turret but again you know because there's foam and crests and everything determining exactly where these things are relative on the ship's halt is going to be a little less precise now you can also measure from the crest to the trough and then just double it to get the total wavelength if you only happen to have a partial picture as in this case although you do have to be careful to make sure that your partial picture does actually show the trough beginning to rise back up again to make sure you do actually have a true half wavelength but if for example we look at this picture of USS Illinois the peak of the first Crest after the bow Crest is about level with the ship's funnel now she's about 3 375 ft long at the water line and scaling therefore suggests that the Gap we're looking at between the bow and the funnel is about 160 to 170 ft which would suggest using the formula that she's doing around about 17 knots now if you look at Illinois's class rating speed of 16 knots you might think oh hang on a minute Dr we've got a bit of a problem with our calculations here but if if you look closer you'll see that Illinois actually managed to get 17 and A2 knots on her trials which means that in this shot she is absolutely booking it but as you can see on a fairly calm C and thus a speed of around 17 knots is entirely possible also this is actually a really nice shot generally it's one of my favorite Naval photos and for one last example that we're going to work out here's USS New Jersey in the late 1960s and you can see an absolutely beautiful wave profile going down the side of her Hull now here you can see there's a Crest right underneath turret one and you can see there's another approximately just underneath the fourth of the port side 5-in gun mounts now the IAS we know are about 887 ft at the waterline and so if you scale from a side profile of the Iowa to those points then that suggests that the ship is moving at a comfortable 22 to 23 knots in this particular photo so there you go as long as you can get a good view of the side of the ship and your scaling is okay with a side profile picture you can now tell roughly how fast a ship in a photo is moving or even in a film if you want to take a still shot now the other principle that I want to talk about today is a fine detail about how large ships turn that I wasn't fully cognizant of until I had a discussion with a serving naval officer who also happened to be a navigational specialist a few years ago but is right there in the pages of night seamanship now that is when a ship that works with a Stern mounted Rudder at least is put into a turn believe it or not it doesn't actually go that way at first now this may seem a little counter in ative but it's such a fundamental part of ship handling that it even has its own specific designation this behavior is known as kick now I will read the relevant part from Knight's seamanship so if you haven't have the 11th Edition this is on page 294 uh if you have another addition it might be on a similar number but not exactly the same page in any case it says when the rudder is first put over and the stern starts to swing the forces resulting from the momentum of the ship and the rudder action tend to move her Sideways from the original course in the opposite direction to the turn meanwhile due to her momentum she will range ahead along the original course for several ship's lengths before beginning to gain ground in the direction of the turn this kick is the reason for the variation between tactical diameter and final diameter which are two other terms we'll look into in a later video the drift angle is variable during this period and does not become constant until about 90° of the turn is completed after the drift angle becomes constant the ship will continue turning at a constant rate and a virtually constant speed now that means that as seen in these diagrams when a ship first puts the rudder over you can see that initially you'll just keep going and the ship will actually turn slightly away from where you want to go so if you want to go starboard and you put the wheel over hard to starboard the B will actually go slightly to port and vice versa if you want to make a port turn and then as the full effects of the rudder take over after a few ship lengths then the ship will start to turn back in the direction you actually wanted to go in the first place and then it you know the turn will accelerate now this is very important in navigation for all sorts of reasons uh for example example if you're in a narrow shipping channel you don't want to ride too close to the edge of it otherwise when you try and turn back towards the center of the channel or perhaps you want to make a turn towards the opposite side if the channel itself is changing course in that direction you run the risk of running ground as the ship will kick slightly taking you outside of the channel likewise if you find yourself in what's going to be a near headon Collision it's actually safer to pass straight down the other the side of the other ship and then turn once you're clear as trying to turn away before you pass down the side of the other ship could cause you to kick towards the other vessel and then Collide it's one of the reasons also why side by-side resupply has to be done with the degree of space between the two ships not just because of wave action and of course it can also affect the exact nature of water ship is doing if you happen to be trying to work out what precisely that ship's Behavior was at the very start of a potentially ordered turn so I hope this short introduction to some of the fundamentals of ship engineering was useful as I mentioned I will be progressing this Naval engineering miniseries generally on Fridays as and when possible occasionally covering things like this from an academic perspective with worked examples and other times like when we look at Armor I'll do my best to rig up some kind of practical demonstration as well in any case thank you very much for watching and see you again in another video

Channel: Drachinifel

Views: 88,839

Keywords: wows, world of warships, HMS Hood, bow wave, ship turning, battleship, warship, ship speed

Id: IxHMtF0cEKQ

Length: 23min 6sec (1386 seconds)

Published: Fri Mar 15 2024