Hydrodynamics and Hull Design: Linking Hull Shape to Powering
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- เผยแพร่เมื่อ 25 มิ.ย. 2024
- A refined hull shape epitomizes the link between tradition and science. When we link the science of ship design with the experience of past ships, we identify the successes and isolate previous failures. This article glimpses into the background of hydrodynamics by exploring the link between the science of Bernoulli’s equation and the shape of ship hulls.
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References
[1] B. Massey, Mechanics of Fluids, 7th Ed., Cheltenham, UK: Nelson Thornes Ltd., 1998.
[2] Wikipedia Contributors, "Propeller Blade Surface Pressure Distribution," Wikimedia Commons, 10 10 2008. [Online]. Available: commons.wikimedia.org/wiki/Fi.... [Accessed 23 10 2018]. - วิทยาศาสตร์และเทคโนโลยี
Im graduate from ocean engineering. If 6 years ago i found this channel maybe i will be the best student
Your content is explicit. I love ur videos.
Hi, I'm a Naval Architecture student from Brazil. I really like your videos. Keep up the good work.
Hi hope you doing well.
I would like to build a 48' loa steel boat and haul is a subject can you advise.
Thank you.
I have to imagine the shape of the stern is probably the most critical part - I've heard for a lot of other vehicles that is the case. Cars the shape of the back end has a much bigger role in total drag than the front, it's all about reducing the total energy in the air behind the vehicle. Dragging a bunch of air or water with it really slows it down, the flow needs to cleanly rejoin and come off the hull or body without excessive turbulence.
Great video!
Good lesson, thanks!
Excellent !!
Great videos.. I would really like to see some video about hydrodynamics and planing hulls. This to me seems an area where there is only very limited information available
Hi, I really like your videos. I don't own a boat but I'd like to see a video on which hull type and shape would give the best, most comfortable ride. I think for a standard 24 foot pleasure boat would be most interesting. Thank you for your time.
I just wondered if a keel shape could passively add lift to the displacement hull favouring hull lift at the aft end, the goal to mechanically overcome the hull speed trough wave at mid caused by for'ard lift riding a bow wave (and the wave trough dipping the stern): ie. the leading keel edge descending elevation forking an upside down Vee, the interior tunnel sloping down and also convexly contoured , closing out at keel bottom the aft end fanning horizontally like a a Y in stubby delta ski/wings.. if it's angle of attack was pitched right there ought be a hydrodynamic hull displacement ratio (interior versus outside) that passes more displaced water volume below the keel than its standing static displacement (doing hydrodynamic Work to create "lift"). Water being denser than air, I think it wouldn't take radical area spans to achieve a realisable advantage.
Could you please help me how could I determine the estimated draught of a double hull and a single boat. It would be a please to hear your brilliant ideas.
Yolando Morro - Phlippines
Hi.
The longest vessel is the faster it goes does work in planning hull boat?
I take design as a hobby of sorts, daydreaming included. Presently I am designing a displacement hull yacht and this info that you give is very useful. I do have an issue. If I don't find a way to place a horizontal propeller shaft with some type of vane for water to smoothly flow towards the propeller, I'm going to have to opt for pods, such as ips or zeuss and I've heard that is not advisable. Any tips will be much appreciated.
Interesting !
Lwr least wind resistance to improve rudder control and keel the headsails to improve sail power. Wing keel and blade for example. Ballast separate from keel line stem to stern.
If I have a common sailing yacht that I add hydrofoils to - how would that affect your math?
How much design goes into the aerodynamics of a ship? Just an afterthought, or a crucial part for the architect? Would be interested to see a video of yours on this.
I wish I could say more effort went into the aerodynamics, but it is more of an afterthought (excluding sailboats). Aerodynamic drag makes up around 2% - 5% of the total drag on a ship. For high speed ships (35+ knots), that can be more significant. And high speed ships do see more aerodynamic design.
One area where aerodynamics play a part: the sideforce on a ship. Large ships have a lot of wind area when viewed from the side. A sideways wind generates significant force. This becomes a large factor in designing mooring systems for the ships and rudders to control maneuvering at slow speeds in port.
Would adding a 1/4 x 2" angle or more to the outside edges of a flat bottom skiff improve the hull performance?
Towards the end you say that at the stern of the ship, part of the pressure from "collapsing" water acts longitudinally towards the ship, REDUCING the total resistance. No matter how I look at it, a moving object will have a zone of high pressure at the front "pushing against it" and a zone of low pressure and possibly turbulences at the back "pulling it back" and both slow it down. The most you could hope for at the stern is less turbulence and less changes in water speed and pressure, but this video sounds as if the collapsing water at the stern was pushing the ship forward. Am I misunderstanding something?
What you imagine as a collapsing zone of turbulent water does not happen when we carefully design the hull with a streamlined shape. The key is careful design, with a very gradual reduction in the hull area. Imagine it more like a wide river slowly expanding. The water velocity gently slows down. As water speed decreases, the water pressure increases (the energy shifts from velocity into pressure). Because the increased pressure is pushing on the aft side of the hull, we see a slight forward push, known as pressure recovery.
This is still a very small change. You can only detect it with precise experiments, or with Computational Fluid Dynamics. But clever designers know about it and design to intentionally create the effect for maximum hull efficiency.
I've been thinking about hull designs for ships recently had an idea for a ship with a long teardrop shaped hull.
Lets say this hull was about 600 feet long and her maximum beam (of around 60 feet) was around 200 feet aft of her bow. Do you think this ship would be more efficient than modern hulls by any chance?
(btw, I'm a 15 year-old aspiring naval architect and I'm just wanting to see if this hull could be practical)
Probably not. But I like the way you are thinking. The teardrop shape is a great beginning. And at 600 ft long and 60 ft wide, you have a length to beam ratio of 10:1, which is considered very fine. You would typically see that ratio on very fast ships. But moderns ships already use variations on the teardrop shape, plus some additional tricks. Try to also incorporate parallel sections into your ship design, as these come almost completely free from resistance. You don't need to taper to a perfect point for the teardrop shape. A flat transom stern can help. You are definitely on the right track. Every naval architect started out experimenting and with different hull designs and trying to make it better. And we pretty much keep doing that for the rest of our career.
@@DatawaveMarineSolutions Thank you for the tips!
That sounds like the hull profile of some higher-performance sailing hulls. I think it would perform quite well, that is the most aerodynamic/hydrodynamic shape, hence a lot of protrusions like rudders are that shape. To build such a ship probably wouldn't be very practical though, considering reduced internal space and the lack of a parallel section. The main benefit of a parallel section, or section of constant cross section, is that it's easy and cheap to build - a series of identical frames that can be mass-produced on the same jig to the same design, the same segment of hull repeated over and over again. All covered by flat plates which are cheaper to make. With your design the cross-section would be constantly changing, most surfaces curved, no two frames alike. This is seen on smaller vessels, like sailing yachts, where this cost is seen as acceptable (not huge as the vessel is much smaller) for the performance gain, but for a large ship I think it would be difficult to justify. Would be low-drag, and very beautiful, but when designing such large ships all anyone wants is for it to cost less and carry more.
ive always heard that water is an incompressible fluid. Does this mean that u cannot change its density by trying to push it, but u can change its pressure when pushing it?
Basically yes. The relationship between compression and pressure change is the bulk modulus. (This can also relate to density with a few conversion formulas.) However, for water, that bulk modulus is so ridiculously high that we see no effective change in density for any normal change in pressure. Technically, the water is compressing when we see a pressure change. But not enough compression to ever effect the density.
Do ice breaking hulls have disadvantages in normal waters?
Absolutely. Ice breaking hulls often require wide flat bows, which is a terrible shape for open water travel. Some icebreakers get around this by designing the ship to operate in reverse when breaking ice. They have a normal shaped bow for open waters, and their stern is shaped for ice breaking.
What hydrodynamic resistances is proportional to.?
The fastest trans-Atlantic trip was made buy a 990ft ship and was set in 1952
All these dudes here in the comments are engineers and naval architects and that and I'm just looking for some inspiration for ships in From the Depths
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So if a nice and smooth and sharp stern design is better, why in the world are new sailboats wider and hacked off in the stern (uglier too)? They all now look like half a boat if looked at from the top. also, they are nearly flat bottomed in the stern and some now have chines.. new designs baffle and confuse me.
They do that for different reasons. Racing boats use the flat wide stern because they sail fast enough to plane on the water, and want a planing stern. Cruising boats do because it creates more internal space, and because the boat sails more upright, making for a more comfortable ride.
Worst teaching video on this subject... Give the "working designs FIRST", then explain the (simplified) equation around them...
Like telling 5th graders that 2 x Pie x R = A , then trying to show them why Pie is relevant ... Instead, show them why Pie is relevant 1st with different circles, and they start to understand the 2, R, and A (rather than trying to figure it out the whole time you are speaking)...
First of all don't use superlative forms of adjectives if you can't prove it. This is the worst practice of criticism. (yes sometimes superlative forms are funny)
Another thing is I have no experience in designing a ship. I'm just a technical interested Person and I think I did understand the explanation. So it might be not that bad.