Former Bayesian captain on sinking, vessel ballast and stability

https://www.sailingscuttlebutt.com/2024/08/27/former-bayesian-captain-offers-insight/

by walrus01 • 2 years ago

58 55 2 years ago

sailingscuttlebutt.com

memming2• 2 years ago

Hahaha. This was a click-bait (for me)! I'm not upvoting. Sorry!

memming2• 2 years ago

I shall update my posterior carefully.

FeepingCreature• 2 years ago

He reasonably updated towards frequentism.

bryanrasmussen• 2 years ago

this is great technical insight in a field that most of us are unfamiliar with.

einpoklum• 2 years ago

baysed.

trhway5• 2 years 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-cot3• 2 years 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.

trhway5• 2 years 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.

AdamN• 2 years ago

Apparently the keel was noisy when down (creaking sounds I'm guessing?) and so they only put it down for sailing upwind.

Really there should be a 'stabilize' button in the cockpit that drops the keel and does the dozen other things that is probably in the runbook automatically so people don't have to think about what to do.

trhway5• 2 years ago

for that amount of money there should be a movable weight machinery to automatically keep the boat stable similar to how cruise ships do. It would also improve sailing performance (and i remember that somebody (Oracle?)several years ago wanted to do that in big races, yet it was prohibited).

Animats• 2 years ago

Linked to this in the discussion a few days ago.

Cthulhu_• 2 years ago

I 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• 2 years ago

Besides 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

WJW• 2 years ago

All 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.

jabl6• 2 years ago

Thanks 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 sailing ship of 59m, 635 tons

- 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• 2 years ago

What sank the Bayesian superyacht in Italy? (nytimes.com)

157 points by rediguanayum 4 days ago | 276 comments

rwmj2• 2 years ago

So 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.

trhway5• 2 years ago

All these classical smoke stacks and ventilation tubes sticking out vertically wouldn't look great on a sleek superyacht :)

rwmj2• 2 years ago

That would work, but I was thinking some kind of ballcock (https://en.wikipedia.org/wiki/Ballcock) built into the ducts.

closewith8• 2 years ago

More 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.

krisoft5• 2 years ago

I’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_poo2• 2 years ago

It'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.

closewith8• 2 years ago

No, the question is whether an active or passive system can be designed (at any cost) which will satisfy each of SOLAS, the flag state and the insurers, and remain operational for more than a few days.

Automatically closing vents must be considered down-flooding points, so when calculation the down-flooding angle, you must consider them to be open (for SOLAS purposes).

The only exception (which is rarely granted) is for ball-type automatic closing air vents, which are not suitable for cabin ventilation as they close with negative pressure.

mpreda• 2 years ago

I don't think it's the engine exhaust, neither the engine air intake.

I think the exaust has possitive pressure when the engine is running which would prevent water from entering. OTOH water entering the engine air intake.. would be quite bad for the engine I guess, so there'd be protection against that. Also both of these (exhaust & intake) are not free to the inside of the vessel, but form a closed circuit with the engine, so there's no way to flood the vessel through those.

So probably we're talking about the engine room *ventilation* openings that would let water in.

bell-cot3• 2 years ago

I think the exaust has possitive pressure when the engine is running which would prevent water from entering.

Imagine a (say) 5cm diameter exhaust pipe, at a 45 degree angle - with exhaust gasses blowing out through the top 3cm, while water runs in through the bottom 2cm. At some point, the cold water starts hitting thicker and hotter pieces of metal. As you put it, "quite bad for the engine".

But from the article, about what happens when the Bayesian heels over too far: "water will start to enter the vessel (usually through engine room or accommodation ventilation ducts)… once this starts the vessels is in serious trouble".

jabl6• 2 years ago

Also both of these (exhaust & intake) are not free to the inside of the vessel, but form a closed circuit with the engine, so there's no way to flood the vessel through those.

Don't know about this yacht specifically, but as I understand it a common solution is for the engines to suck in ambient air from the engine room.

So probably we're talking about the engine room ventilation openings that would let water in.

Likely yes. And probably(?!) there were watertight bulkheads around the engine room, so by itself the engine room flooding might not have sunk the boat (assuming doors/hatches were closed), but if combined with other downflooding into the living quarters (doors, ventilators etc.) it would have accelerated how quickly it sank.

closewith8• 2 years ago

To a rounding error, all marine diesels have their intake in the engine compartment, not with any kind of closed circuit.

Especially for sailing yachts, the exhaust is almost always wet (below the waterline).

K0balt• 2 years ago

From my perspective as a former captain of a 20m schooner, a traditional rigged boat much, much less liable to suffer a knockdown such as befell the Bayesian, it’s insane to me that the angle of vanishing stability was only 90 degrees on such a ridiculously tall vessel. That means that if that mast ever touches the water it’s not coming up. Period. And that mast is a huge lever , even without sails raised.

This is a boat that was never designed to weather a bad storm, where unpredictable things are very likely to happen.

And it starts to flood at 45 degrees while in normal operating trim? That is just nuts. It’s not that hard to put all of the ventilation on the centerline, and a diesel engine won’t flood a boat through its exhaust.

So many design compromises on what could have been a real seagoing vessel you could trust to carry your family anywhere in comfort and safety, just for the sake of some misguided idea of opulence. In ships, beautiful is as beautiful does. A sleek coffin is an ugly ship indeed.

I would not have felt safe sailing that vessel in anything other than well timed passages with no weather nearby.

It really drives home the difference between a boat that is designed to stand up to whatever it might encounter vs a showpiece that is designed to look impressive but cannot face the kind of adversity that a working ship will be exposed to on a routine basis.

Clearly these yachts are designed to be operational in pleasant conditions only and to hide in shelter when the sea shows it’s teeth. What a stupid waste of resources. A fake ship.

the5avage• 2 years 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)

kleiba• 2 years ago

Is this article on HN because of the word Bayesian?

quietbritishjim• 2 years ago

I 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• 2 years ago

Hacker 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• 2 years ago

Really? I don't remember anything like that apart from this particular boat.

vdvsvwvwvwvwv2• 2 years ago

Depends on your priors

vertis• 2 years ago

I 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.

vdvsvwvwvwvwv2• 2 years ago

If you are gonna have ads, do it like this site. Apart from 1 Google ad it is doing it 1999 style!

pas• 2 years ago

and uBlock Origin left in the old school one :)

p3rls• 2 years ago

The thing is that the yachting and fishing niche is so high-end that these ads probably pay more than 98% of websites with similar traffic numbers

Former Bayesian captain on sinking, vessel ballast and stability

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