HIDDEN DANGERS TO STABILITY: Angle of Loll
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- Опубликовано: 30 июл 2017
- PANIC! Well, at least severe concern. Angle of loll shines like a bright red warning sign, indicating serious stability problems. You need to track down this cause, because the next warning may be when your ship capsizes. Today we discuss an angle of loll (AOL): what it is, how to find it, and what to do about it.
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I don't own a boat, have no connection to marine architecture, but simply can't stop watching your videos. I just like the fact that you take complex subjects, make them understandable, but don't dumb them down. As a former technical trainer, I know just how difficult that can be.
Keep up the great work.
thanks for the explanation.
Que buen video compa, Gracias!!!!!
Watching your videos & observing mass locations made me realize just how "out of balance" my families pristine early-seventies fiberglass Seaswirl 16 ft outboard glass is....Firstly is the 50 HP rating for an engine off the transom. Engines circa 1973 were typically four-cylinders, inline or V4...upgrading to newer engines made for three or two cylinder engines, at a considerable weight savings, less weight on the transom. Further, the location of the fuel-tank rides very far forward & up way too high ( a rectangle whose floor is 18 inches off the floorboard)....Then the back to back seats common in that era, also too far foreward...I always felt a degree of strangeness as I learned boating circa 1974 in this boat & later (90s) new boats, the newer boats much more stable. Now I know where the stability problems lie.
Lol.
Love your videos mate.
I once drove a Buick that definitely had a large angle of loll
lol
The Buick Dockmaster
The Captain of the Costa Concordia had more than an hour of the Angle of Loll and didn't issue the order to evacuate. A lot of people died because of that decision while the captain escaped the boat.
@ "Nick the naval architect": what are typical heel angles in concrete numbers that can be expected in typical offshore storm conditions (not including hurricanes)? I'm wondering how much room for error there is between actual typical heel angles and design capsize angles. The latter I can calculate, but without knowing how steep in concrete numbers big ocean waves tend to be it's hard to know how good of a given design capsize angle is good enough.
I'm referring to power boats, not sail boats with deep keel ballast. Therefore lever forces on sails due to inadequate reefing are not a factor, so my question is purely about fluid dynamics of waves, not wind influence.
Example numbers: power cat 4x10 meters with 2.5 t displacement, design draft 0.5 m, initial stability: vertical center of buoyancy 0.30 m, COG 1.0 m, transverse metacentric height 8 m. COG as "fixed" = no free fluid surfaces taken into consideration.
Thanks in advance if you take the time to answer. Nice and valuable channel by the way!
I have not understood a word. But then, I am a sailor...
Could you explain what free surface moment is and why it would cause an angle of loll?
I get the danger of sloshing liquid but that moves the centre of gravity sideways but not necessarily razes it. More specifically (to my understanding), the tanks are part of the design, if you load properly, you should not need to consider the tanks. They may cause a list but not a loll.
There is something I don't fully understand here.
That is an excellent idea. I will have to create a video on this. For now, I will give a simplified explanation. First, there are two problems with liquids in tanks: free surface moment and sloshing. Sloshing comes from the momentum of the liquid as it hits the sides of the tank. Sloshing is not a major concern except for tankers where they have huge cargo tanks full of liquid.
The other issue is free surface moment. And you described it perfect. As the ship heels over, the liquid in the tank shifts, and the center of gravity moves sideways. For small angles, that sideways shift in the center of gravity follows a predictable mathematical formula. And as a weird quirk of mathematics, that formula exactly mirrors one of the formulas to vertically raise the center of gravity.
So to account for tanks, we use the shorthand version of the mathematics and do all the stability calculations with a "virtual center of gravity." That is just the physical center of gravity, plus a correction to account for the tank free surface.
And to the last part: yes, the tanks are part of the design. And yes, if you load them properly, the ship should be safe. But tank load is also about drawing from the tanks in the proper sequence. For example, a ship may have 4 - 6 pairs of fuel tanks. But we only design the ship to have one pair slack at any time. All the others are either full or empty. Not every captain understands how critical it can be to stay within those design limits.
Some scientifically discreditted examples of ships (hulls/usages/loadings/adaptations) with dangerous Loll might have been useful.
[However, just about every capsize would probably qualify and does represent a serious time investment on your behalf.]
the angle of LOL
Has anyone ever told you that you look like a bond villain?
calling a naval architect certainly would be Much Better than capsizing ... sad to say, there are actually vessels out there witch require such concern.
probably all vessels do have some angle of loll, masked by keeping it from such a sea state....but safely figuring out what that sea state would be, definitely would require a naval architect.
What does the 4 letter acronym LOLL mean as in "Angle of Loll"? Not what is it, but what do the letters L-O-L-L stand for?
Sorry, it isn't an acronym in ship science. It literally means the angle of heel that a ship rests at (preferably an angle of zero). If you are looking for an acronym, Urban Dictionary describes LOLL as "Laugh Out Loud Literally".
www.urbandictionary.com/define.php?term=LOLL
Hi Nicholas, I have read your answer and I am still not clear as to why the word “Loll” is used in phrase AOL? What is the etymology of the term “Loll” if it is not an acronym used in ship science?
I sure that ship architects of old did not refer to this point as the “angle of Laugh Out Loud Literally!” “Did they say to themselves; hum, this terms sounds a bit too long, so let’s shorten this to Angle of “Loll” instead.” Ready!
I am just guessing, but I wonder if use of the term “Loll” has its history in the position of the point on the GZ curve. That is to say, “At the AOL, the ship movement is at a ‘Lull’”, (a temporary interval of quiet or lack of activity - note spelling change).
Other than a the use of “Lull” as a description of a drop in wind speed, here in the Western Hemisphere “loll” in not really used in common speech nor does it have a familiar meaning if you confront a person with it in a sentence. As it was not familiar to me, I consulted a dictionary and found the following:
Lollen "to lounge idly, hang loosely," perhaps related to Middle Dutch lollen "to doze, mumble," or somehow imitative of rocking or swinging. Specifically of the tongue from 1610s. Related: Lolled; lolling. As a noun, from 1709.
So could it be that the “angle of loll” refers to the point that is reached when loading a vessel where there is no tendency for the ship to rock or sway as in a “loll” between negative and positive stability?
Interested in your thoughts on this?
Well, I can't speak as an expert on the etymology of this, only on the science. But I think you are on the right track with comparing lull to loll. I can tell you that in the maritime world, we take an almost perverse pleasure in inventing our own cryptic vocabulary. Many of the words mutate due to abbreviations. Example: foc'sle (pronounced Fok-Sill) is the forward space on a ship, above the main deck. But it started as forecastle.
It is fair to describe angle of loll as the balance point between negative and positive stability. And you could compare that to a lull in the wind. I suspect it started out as LULL, and got mutated over time. I suspect we call it a LOLL because we wanted a special word for this angle. Mainly because angle of loll really is a bad thing.
I can't really say that we have a hard and fast vocabulary in the maritime world. We are an international group, with people from every country all trying to speak English as the common language. Spelling errors are very common. And sometimes, we need to invent new words to describe increasingly specific components on a ship. I learned to be flexible with my vocabulary in the maritime world.
Loll is simply a word in the English language meaning to hang loosely or droop. "Stop lolling about there soldier!".
lol
This is a DANGEROUSLY naive and misleading offering. "Call a naval architect"? Never.
Call a Master mariner, a marine superintendent or a senior deck officer. At least he/she will know in practical terms immediately and SAFELY what to do to correct a loll condition and, FAR more important, what NOT to do ( which this naval architect, despite the title, totally forgets to mention! ) And an experienced deck officer or super will solve the problem without all the self-agrandising academic twaddle.
sixmagpies, did you know that G has to be below M ?
Would a master mariner know about a stability curve ?
LOL. (No pun intended.) You must be joking. Any master, or 1st mate for that matter, must know how to calculate stability, roll rates etc., as they have to use them almost daily. Yes, amongst a myriad of other stuff, any real master-mariner knows stability, inside out. That is why he warrants the honorary "Captain" while ashore as well as aboard, and for life. Naval architects, on the other hand, do their brilliant work, 9-5, using a clever computer, and then sleep soundly at home in their bed, with very little risk of rolling over or drowning.
By the way, lots of metacentric height isn't necessarily wanted, especially if one likes comfort. Great ocean liner have tiny MetaHt measurements, sometimes measured only in a few inches, and many Far Eastern fishing vessels operate in a permanent 'loll condition' in some of the worst seas on earth.
One can understand your comment, though possibly not the unnecessarily rather hypocritical and plebeian personal insult.
Having spent half my professional life in construction correcting the myriad impractical, and very often, life-threatening mistakes in design offered by young naval architects with no sea time, one feels somewhat qualified to comment.
The point here is that during this apparently informative video, he doesn't actually explain (ie. warn) how properly and safely to calculate and correct a loll condition, bearing in mind momentum. Hence my initial comment.
The second comment comes from someone rather naively and amusingly suggesting that a master or mate wouldn't even recognise a stab.calc. when, in fact, we use them almost continually.
In the final analysis, the point is that, in extremis, one should call an experienced master mariner, and not a naval architect.
completely agree, quite silly recommendation on 05:45
It's clear from the comments that Sevenmagpies places no value in naval architects, so there is not much point in debating your comments. There are specific reasons that I did not describe a full procedure to correct an angle of loll. If you feel this video was insufficient, you are welcome to create your own video rather than offering negative criticism. And yes, I think many master mariners can help with an angle of loll. Many master mariners possess just as much knowledge as a naval architect. I also encountered many people with the title of "captain" who did not even understand free surface moment. My experiences have shown a mixed bag of capabilities with mariners. If you feel they are misrepresented, feel free to contribute something more than criticism.