5 ms·
Former Bayesian captain on sinking, vessel ballast and stability
- memming 2y agoHahaha. This was a click-bait (for me)! I'm not upvoting. Sorry!
- memming 2y agoI shall update my posterior carefully.
- FeepingCreature 2y agoHe reasonably updated towards frequentism.
- bryanrasmussen 2y agothis is great technical insight in a field that most of us are unfamiliar with.
- einpoklum 2y agobaysed.
- trhway 2y ago> The precise mass of this ballast I do not recall, but it’s probably around 200T or so. In the center part of this box there is the moveable keel, which weighed around 60T and extended almost 6m below the keel box when lowered. This arrangement means that the majority of the righting moment of the vessel comes from the main ballast… the moveable keel acting more as a centerboard to reduce sideslip under sail (leeway)… draught 4m without the moveable keel. The standard ballast is 140t, added 30t - 170t, not 200t. Say center of gravity of that ballast is 3m down from the center of stability - thus 510 tons x meter momentum. The moveable keel - 60t, center of gravity say in the middle or significantly lower (usually it would be very close to the bulb at the bottom end of the keel), i.e. at least 6-7 meters below the center of stability - thus 360-420 tons x meter momentum. So, while technically true, 500 being the major part, having 900 instead of 500 would probably have been much better in that situation. >The Angle of Vanishing Stability is the angle of heel at which the vessel righting moment reaches zero, meaning that the vessel will not return to upright. Again, I forget the actual numbers for this, but the figures would be around 90 degrees with the moveable keel lowered and 75 degrees with it raised. yep, and without lowered keel the chances of the gust putting the boat into those 75 degrees is much higher.
- bell-cot 2y ago> yep, and without lowered keel the chances of the gust putting the boat into those 75 degrees is much higher. If the downflood angle is 45 degrees, that does not matter. He notes that you'd have to turn off the generator & HVAC before closing the vents, and those vents give it the poor downflood angle.
- trhway 2y ago>If the downflood angle is 45 degrees, that does not matter. it does matter a lot - the larger momentum, the sooner it will return from the 45 back to 0, and thus less flooding. With less momentum and thus slower return it may though not return at all if the flooding speed would increase the list faster than the momentum would righten the boat back.
- bell-cot 2y ago(I assuming you mean "moment" when you say "momentum" - https://en.wikipedia.org/wiki/Moment_(physics) https://en.wikipedia.org/wiki/Moment_(physics) ) Once you've got water pouring in, all the stability angles start changing. Usually very fast. And returning "back to 0" would require both the storm suddenly calming, and floodwaters to be free to (in effect) move to the ship's centerline. (Some hull shape will do that, with limits - but I'm not a naval engineer, and don't have a useful real-world understanding of this.) I think the critical thing here would a graph showing the ship's righting moment and the storm's heeling moment, both vs. angle of list, with the former shown both with and without the keel extended. Actually, a series of graphs - the wind wasn't constant, and the righting moments changed as the ship flooded. Those could answer the "would extending the keel have saved the ship?" fairly well. Flip-side, extending the keel would have changed the ship's draft from 4m to 10m. The ship was dragging its anchor. I don't have a chart of the waters the ship was in, but running its deep keel into the bottom could also have ended badly. Has that consideration been mentioned? EDIT: Here's the former captain's take on this, from the article: > The Angle of Vanishing Stability is the angle of heel at which the vessel righting moment reaches zero, meaning that the vessel will not return to upright. Again, I forget the actual numbers for this, but the figures would be around 90 degrees with the moveable keel lowered and 75 degrees with it raised. > The Downflooding Angle is much more important though in the scenario we are talking about. This is the angle of heel at which water will start to enter the vessel (usually through engine room or accommodation ventilation ducts)… once this starts the vessels is in serious trouble as stability is quickly reduced or lost due to the flooding. > The downflooding angle for Bayesian was around 40-45 degrees… much less than the AVS. So, unless the vent dampers are closed (which with HVAC systems and generator running they would NOT be as they need to be open for that), the vessel will start to flood rapidly if heeled more than the downflooding angle. My initial response to you was probably based on his strong emphasis on downflooding angle, vs. vanishing stability angle.
- Animats 2y agoLinked to this in the discussion a few days ago.
- Cthulhu_ 2y agoI know little to nothing about sailing, but I didn't realize they had 200T (tonnes? 200.000 kilos?) of ballast, and that some of it is movable to well below the waterline.
- tromp 2y agoBesides the metric ton of 1000kg there are various others that differ slightly [1]. So that is indeed approximately 200,000 kilograms. [1] https://en.wikipedia.org/wiki/Ton https://en.wikipedia.org/wiki/Ton
- WJW 2y agoAll of it should be well below the waterline, it's what keeps the ship upright against the heeling torque from the sails. The whole ship displaced "only" about 540 tonnes (including the ballast), which I think is fairly light for a vessel of that size. As a comparison the navy vessels I used to sail on came in at 6000 tonnes for 150 metres, so 540 for 54 metres is quite a bit lighter.
- jabl 2y agoThanks to the square cube law, you can't linearly extrapolate the displacement from a 150m ship to a 54m one. Looking at some random ships in roughly that size one can see e.g. - https://en.wikipedia.org/wiki/Stavros_S_Niarchos https://en.wikipedia.org/wiki/Stavros_S_Niarchos sailing ship of 59m, 635 tons - https://en.wikipedia.org/wiki/Gepard-class_fast_attack_craft https://en.wikipedia.org/wiki/Gepard-class_fast_attack_craft German naval ship, 58m, 390 tons. Considering it was a yacht with relatively fine lines, even taking into account the ballast, 540 tons seems about ok.
- jakub_g 2y agoSee also: https://news.ycombinator.com/item?id=42009570 https://news.ycombinator.com/item?id=42009570 What sank the Bayesian superyacht in Italy? (nytimes.com) 157 points by rediguanayum 4 days ago | 276 comments
- rwmj 2y agoSo it's not possible to design ducting for HVAC/engine exhaust that either closes automatically at a certain angle, or has some mechanism that lets out gases without letting in water? I assume people have thought about this, but from the outside it doesn't seem like too hard of a problem.
- trhway 2y agoAll these classical smoke stacks and ventilation tubes sticking out vertically wouldn't look great on a sleek superyacht :)
- rwmj 2y agoThat would work, but I was thinking some kind of ballcock (https://en.wikipedia.org/wiki/Ballcock https://en.wikipedia.org/wiki/Ballcock) built into the ducts.
- closewith 2y agoMore or less any clever tricks at sea have been tried and tested and found unsuitable. In particular, almost any non-positively actuated mechanical valve exposed to sea air will seize in days.
- krisoft 2y agoI’m sure it is possible. One surprising thing i hear about yachts (or not surprising I guess, depending on how you look at it) is that money is not a limit when it comes to guest accomodation but they are very much pinching every penny when it comes to anything else. So the question is not “is it possible to design automatically closing ducting” but “what is the cost of doing it”. And in general everything the guests interact with or experience will be exactly how the owner wants it, while everything else will be done to the minimum quality required by the classification rules.
- short_sells_poo 2y agoIt's not (just) cost saving. Having owned a yacht, everything breaks all the time. The environment is extremely harsh on everything. Seawater is corrosive. Even high quality stainless steel (expensive!) will corrode. Sealife is invasive. Every nook and cranny is under constant assault from all sorts of weird little critters. The most robust solution is to keep things as simple as possible. Any bells and whistles you add will become liabilities very quickly, and if crucial systems depend on these bells and whistles, you can quickly get cascading failures. I learned in about 2 months that you want the most crude, easy to repair and reliable solution to important parts and you want them cheap - because you'll be replacing them regularly. Expensive solutions will provide very little relief from this (if any at all). If the TVs in the guest rooms break regularly because of constant vibrations, that'll annoy the guests, but the ship will float and go forward. If your fancy fly by wire engine controls corrode and you are out at sea, it's mayday time. A lot of smaller boats still use mechanical wire actuation because it can be mended literally with a string.
- the5avage 2y ago> As it pushed the boundaries of aluminum mast construction there were lessons that had to be learned over the years, but the result was a robust and well controlled rig in the end that performed well, within the limits of the design. The mast of this ship was slightly higher than that of the Preußen, one of the biggest sail ships ever build. While it clearly worked for a while, it shows how insane the design actually was https://en.m.wikipedia.org/wiki/Preussen_(ship) https://en.m.wikipedia.org/wiki/Preussen_(ship)
- kleiba 2y agoIs this article on HN because of the word Bayesian?
- quietbritishjim 2y agoI think it's because the Bayesian was the boat that sank killing its owner, UK entrepreneur Mike Lynch. The boat was called the Bayesian because he was a mathematician and that was the basis of his career. It's also interesting because the boat was notable for having the tallest mast of its kind, and then sunk partly (one would guess) because of that. The boat sink quickly because hatches were left open in the warm weather. There was also discussion of weird weather phenomena being the cause. He was also in the news shortly beforehand for fighting US prosecutors tooth and nail against a fraud case and recently beating them. Of course there are conspiracy theories that the two are connected, especially as his business partner died within a week while out jogging! The whole thing is pretty interesting overall.
- beAbU 2y agoHacker News users have a slight penchant towards seafaring vessels owned by rich people that, all of a sudden, find themselves unable to maintain their seaworthiness.
- AlexeyBelov 2y agoReally? I don't remember anything like that apart from this particular boat.
- vdvsvwvwvwvwv 2y agoDepends on your priors
- vertis 2y agoI don't think so, I think it's a genuinely interesting piece of information and loss of a yacht. Most smaller (e.g. 36ft) yachts are very hard to sink, often with human error being the most likely problem (i.e the vessel itself is safe and seaworthy). Bigger yachts with commercial crews have to reach an even higher bar. This becomes interesting from a number of facets. Engineering failure, human error, weather.
- vdvsvwvwvwvwv 2y agoIf you are gonna have ads, do it like this site. Apart from 1 Google ad it is doing it 1999 style!
- deleted 2y ago[deleted]