4 ms·

> 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 weighe

by 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.
    - jabl 2y ago
      > 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? It was mentioned in some article that the wreck lies 50m deep, so it seems that even with the keel extended they wouldn't have been in imminent danger of grounding.
AdamN 2y 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.
- trhway 2y 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).
  - 1R053 2y ago
    how fast do these machineries move? as I understand the weather scenario the wind direction was changing rapidly by more than 90 degrees at hurricane level. That means, the boat was unable even under power to redirect into the wind timely enough. The key question is, how much side wind can the design withstand without getting pressed into more than 45 degrees. obviously lowering the keel affects this a lot, as there is much difference in leveraged 60 tons vs non-leveraged.
    - trhway 2y ago
      say moving 100tons 10m, like from one side to another, in 10 seconds - that, acceleration and deceleration, takes 200KWt - half the Tesla's electric motor. It is horizontal. As we may have heeling, the worst case - raising 100t vertically 10 m in 10 sec - 1000KWt, 2-3 Tesla's electric motors.

by trhway 2y ago

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.
  - jabl 2y ago
    > 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? It was mentioned in some article that the wreck lies 50m deep, so it seems that even with the keel extended they wouldn't have been in imminent danger of grounding.

AdamN 2y 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.

trhway 2y 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).
- 1R053 2y ago
  how fast do these machineries move? as I understand the weather scenario the wind direction was changing rapidly by more than 90 degrees at hurricane level. That means, the boat was unable even under power to redirect into the wind timely enough. The key question is, how much side wind can the design withstand without getting pressed into more than 45 degrees. obviously lowering the keel affects this a lot, as there is much difference in leveraged 60 tons vs non-leveraged.
  - trhway 2y ago
    say moving 100tons 10m, like from one side to another, in 10 seconds - that, acceleration and deceleration, takes 200KWt - half the Tesla's electric motor. It is horizontal. As we may have heeling, the worst case - raising 100t vertically 10 m in 10 sec - 1000KWt, 2-3 Tesla's electric motors.