2 ms·

>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 t

by 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.

by trhway 2y ago

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.