Stability FAILS at Seakeeping: Why Stability and Seakeeping Don't Mix
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- čas přidán 24. 07. 2024
- Stability and seakeeping are frequently misunderstood. To understand the limits of these sciences, we must unveil the motivation behind their development. How to guarantee ship safety on an uncertain ocean?
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References:
[1] Maritime Safety Committee, "Explanatory Notes to the International Code on Intact Stability, 2008," MSC.1/Circ.1281, London, UK, 9 December 2008.
[2] US Code of Federal Regulations, "Weather Criteria," 46 CFR 170.170, Washington, D.C. USA, 2018.
[3] US Code of Federal Regulations, "Passenger Heel Requirements for a Mechanically Propelled or a Non-Self Propelled Vessel," 46 CFR 171.050, Washington, D.C., USA, 2018.
[4] J. Journee and W. W. Massie, Offshore Hydromechanics, First Edition, Amsterdam, January 2001.
[5] Wikipedia Authors, "Hurricane Rita Lake Charles Radar," Wikimedia Commons, 24 September 2005. [Online]. Available: commons.wikimedia.org/wiki/Fi.... [Accessed 26 October 2018]. - Věda a technologie
Nick I love your videos. I always learn something about a very niche subject. It's super interested in that field.
I love learning the general engineering terms. Having watched Nick, I could have a conversation and not feel clueless. I'm sure once I win the lotto, this will help when ordering my Yacht.
You might've defined "seakeeping" at the outset. At the practical end, I regularly shipped between NZ and SF. The last time was aboard Argentina Star in 1998. During winter, we regularly had +/- 38 degrees rolls resulting from swells in the Pacific NW. Once you know the ship and cargo can handle it, you just wedge yourself in beneath your bunk and dresser and flake out. The cook always had a hard time, tho. On the other hand, on my Schooner Talofa in SF bay, 38 would've been rare, only used to wash off the deck or scare the tourists.
Thank you I love stability talk I recently put together a 26 foot carver cabin cruiser that had a v8 and a upper and lower bridge all on a 8 foot beam, top heavy or tender in a sloppy sea state, I turned it into a LRC with a small diesel and as low a CG as possible, I read everything I could find on initial stability Vs ultimate stability, although I believe I ended up with a very slow stable boat I would love to here you talk about the two stabilities and how they work with each other especially on smaller vessel s under 100 feet or even less or completely non size relative at all as I assume size sorta does not matter if all comparisons are relative. thank you sir
I love watching Nick’s videos as I always learn something new!
What about self-righting vessels? How realistic is that for recreational yachts. I’m thinking specifically of the Cape Horn Trawler style yachts that claim tank tested to be self righting.
It's possible. A self righting yacht can be achieved with some careful hull design and a watertight deckhouse. However, the bigger problem with self-righting is to ensure the engine still works when you come back up. That takes a much more thorough design approach.
Good video. I hope to see more videos on sea keeping.
Me too. I have ideas for several videos I want to produce on that. Just a matter of priorities.
Nick, another great video. Thank you. Will you consider making GHS video tutorials in Seakeeping?
great lesson
thanks bro
Love this guy!
Thank you.may you tell about seaworthy more?I am looking for a boat without stability but seaworthy
Thanks for this video. Before this, i woulda thought that stability and seakeeping were the same thing. But can you give exact definitions of those two terms? I'm still not sure what's the exact difference between them. Is seakeeping more about how stable the ship is when moving thru waves (minimizing pounding, rolling, etc.), whereas stability is more about static stability like righting itself from heeling over?
Pretty close. In seakeeping, we typically assume the ship will always return to upright. The mathematics for seakeeping actually break down if we get to motions large enough to consider capsizing the ship.
Stability is more about static conditions. That is the largest difference. In stability, we rarely consider the ship's momentum. Almost everything is a static analysis, which can still achieve quite a lot.
Has anyone developed software to analyse wave length and optimise ship speed and course to the conditions? Seems like things like resonant frequency of the hull and hull speed should be avoided by changing ship speed and course to avoid wave amplitude increase
Yes. The larger ships pay for a weather routing service. Meteorologists give the ship daily predictions for the weather along their route. And that feeds into software so the captains can plan the best route around the weather. For cases like cruise ships, this means they can plan the best course to ensure a smooth trip. For other ships like bulk freighters, they can plan to minimize fuel consumption. None of this is cheap, but it works very effectively.
I learned something new!
So what I conclude from this: The most powerful tool is analyzing the difference between ships that did sink in storms and those that didn't, finding a way of measuring such quality, and based on which ships did and didn't sink designing (and legally requiring) ships to be more like those that didn't sink in this regard? Makes sense, the only way humans ever learn anything is by trial and error. What makes humans so capable is that we are at least somewhat good at learning from the errors of others.
I would disagree with the assertion that "no ship is unsinkable." While some have falsely made such claims, I'd argue that it is possible for a ship to be unsinkable - if it is built in such a way that no matter how much water gets into it it will remain at least partly afloat. This is true for many smaller vessels that are filled with foam, not as common for larger ships but I can think of some somewhat larger examples. The MV Joyita was a ghost ship found swamped but afloat thanks to a cork-lined hull (intended as insulation for refrigerated cargo) and cargo of empty fuel drums which acted as flotation cells. So she floated, but all crew went missing somehow.
This video may be good for the novice on ship stability and ship hydrodynamics.
If one really wants to know more about it, which is at present still beyond the ability of human intelligence, please go into probability theory of capsize, and better still, for damaged stability of different ship types and marine structures.
Lyapunov theory that was available more than one hundred years ago was ignored until nowadays with high speed computers, and it is now at the the fore-front for the use of Chaos theory for the evaluation of ship stability, both for intact and damaged ships and different types of marine structures.
Do not be misled by someone who tells you we know what we are doing and how good the regulations are in reflecting the facts. Keep up with your knowledge by reading more nowadays research papers.
just like how they started armoring the unharmed parts of warplanes that returned rather than harmed parts....
Yes, the warplane example shows a particular hazard of your assumptions.
They began by looking at where aircraft were getting hit and adding extra armour there.
But at some point they realised 'wait, we're only checking the aircraft that survived a battle, not the ones that never came back'
And since they couldn't realistically check what went wrong to crashed aircraft...
But could see what kind of damage the aircraft that made it back had...
It became apparent that the armour has to go where the returning aircraft were LEAST damaged, since the damage seen on aircraft that made it home clearly wasn't critical...
@@angrydragonslayer I fail to see the parallel.
This is more like armoring a bunch of aircraft in random places and seeing which ones come back alive- then imitating the survivors, isn't it?
EDIT: Never mind. Thought of a parallel. If you have a certain flaw in a ship that causes it to list frighteningly, even in rather mild storms, it may cause the master never to take that ship out in heavier weather- unless he is very experienced (pushing up the survivorship when it IS taken out). Whereas another ship, that is in truth more stable (but appears so as well), might be taken out more often in severe storms- even by novice masters- and thus sink more often.
So, if you design only based on Survivorship, you gst Survivorship bias. You may actually be designing LESS stable ships simply because they frighten masters who are novices (and really SHOULDN'T be taking ANY ship out in a storm) and thus survive a higher percent of severe storms (due to only seeing storms under skilled masters).
I wonder if the calculations factor in years of master experience, or average number of prior accidents a captain has had?
@@Supadubya my reply was definetly underdeveloped to a point of causing misunderstandings but i'm glad that it caused you to consider additional factors
Why doesn't this channel have 100k subs
Lwr least wind resistance of the hull below water line. Should be required and righting ballast should be required. Why are regulations devoid of lwr least wind resistance or keel line stem to stern academic.?
Yes, but shouldn’t that be fine tuned by now due to the data available now?
Also, I understand as a business you shouldn’t be focused on sea keeping however shouldn’t there be a body that is testing new methods, and parameters?
Yes, there are organizations developing new stability criteria. The International Maritime Organization (IMO) brought out a major change for damage stability criteria about 20 years ago. And there are proposed changes for intact stability criteria.
One thing to remember: research is expensive, and the entire shipping industry depends on extremely thin margins. Research still happens, but no one can afford massive testing and research projects these days. So who pays for the big research? Ultimately, it's ordinary consumers like you and me. The cost of shipping is built into every product we buy. If we want safer ships and further research, the first thing we need to do is accept an increased price on every single product we buy.
Great
How do I get in touch with this guy?
My contact details are on my website: dmsonline.us/contact-information/
For business inquiries, you can email me at sales@dmsonline.us
What about SWATH vessels?
Excellent question. See my SWATH video for a general discussion about SWATH vessels: czcams.com/video/jJAHyDl6KS8/video.html
I feel a little nerdy.
Submarines, just travel under the weather. Simple