2 comments on “A Brief Look at Submarine Stability

  1. “Submarines are typically designed to have their center of gravity (CG) in the center of that cylinder, thus when fully submerged, their centers of buoyancy and gravity coincide, leading to an extremely stable state (think taking the rock from earlier and hugging it against your chest while underwater, you no longer feel like you’re going to tip over!).”
    THIS IS UTTER RUBBISH; that would give a submarine that would spin freely in the water! The CofG must be well below the CofB to achieve stability.

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    • Firstly, we would like to ask you to respectfully state your opinion in kinder terms in the future, as that is how our comment sections are run. If you respond back with the same level of rudeness, your comment will not be approved.

      Secondly, this is not “rubbish”; at a high surface position (as shown in the figure), the CB is well below the CG, making submarines inherently unstable at the surface (and especially in high surface positions). This is a major reason that submarines typically only take on low surface positions (especially in rough seas) and only do so when absolutely necessary, where the CB is shifted closer to the CG. The more involved details of submarine stability (especially at the surface) are beyond the scope of this post, as they require discussions of freeboard, metacenters (arguably more important than the CB), 3-dimensional stability, reserve of buoyancy, and much more. I would be more than happy to point you in the direction of a dozen or so good sources of literature/otherwise educational material detailing these considerations, ranging from the introductory level to considerably more complex. If you just want a quick show of proof, then here you go:

      “At first sight the condition for static heel stability requires that the centre of gravity should be below the centre of buoyancy so that when the ship heels a positive restoring moment is applied to return the ship upright. This condition applies to a fully submerged submarine but is not a necessary requirement for a surface ship.” [Concepts in Submarine Design (Burcher, Rydill, Series 2) Cambridge Ocean Technology Series, pp. 277]

      Furthermore, regarding your assertion that the submarine would spin freely: you are neglected some very important submarine features. Namely, you are neglecting the inclusion of non-uniform hull shapes, decks, and perhaps most importantly control surfaces (both fixed and variable position), which are detailed lower down in the post. All of these control surfaces help to stabilize the vessel and resist everything from transmitted torque to deep ocean currents. Believe me, I am speaking from both knowledge and experience regarding this.

      In short, you are not correct in your assertions, and I hope the above discussion can help clear that up, but (as I said before) I would be more than happy to point you towards much more detailed sources for further clarification, as I am a bit too busy to explain this whole thing on here, unfortunately. There is one thing that you have helped with, however, as I noticed some confusing wording (that was representative of a bit of an idealized state) in the post now that you quoted it and will be changing the wording to make things more clear, so thank you for that and enjoy your day.

      As always, thank you for reading and commenting!

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