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Re: [PSUBS-MAILIST] A Solution
Joe - it looks like I misspoke myself... that'll teach me to send emails without
reading them first.
Correction:
The metacenter is a point established at the intersection between a vertical
line drawn upwards from the instantaneous center of buoyancy and the vessel
midplane. The metacentric height is not the length of this line, but rather the
positive length from the vessel CG up (along the midplane) to the metacenter.
If this line intersects CG (as it will when the vessel is exactly vertical), the
vessel has zero stability at that point. If the metacenter is below CG, the
vessel is unstable. If the metacenter is above CG, the vessel is stable, and
the metacentric height is a measure of the stability.
-Sean
Quoting Joseph Perkel <joeperkel@hotmail.com>:
> Sean,
>
>
> So then with known values of weights, moments and arms, it would be a
> relatively simple affair to mathematically rule this in or out.
> Anecdotally...it's looking pretty good, since you can counter those high
> moments with low slung weight between the pontoons....if it proves
> necessary.
> I will start work on that model when I get the sub design finalized. The CAD
> program will calculate volume of materials, so starting with known densities,
> I should be pretty damn close in the estimations.
> Joe
>
>
>
>
>
>
> From: "Sean T. Stevenson" <cast55@telus.net>
> Reply-To: personal_submersibles@psubs.org
> To: personal_submersibles@psubs.org
> Subject: Re: [PSUBS-MAILIST] A Solution
> Date: Mon, 6 Nov 2006 12:38:13 -0800
> >Stability is not that complicated. Fully submerged, it just means CB must
> be
> >above CG. On the surface, or at any degree of partial submersion, CG can be
> >above CB, provided that as your vessel rolls, CB shifts outboard so as to
> create
> >a moment arm about the center of roll which counteracts the moment arm
> created
> >by CG. Imagine your vessel as having a plane amidships, which rolls with
> the
> >vessel. The vertical distance between the instantaneous CB (which changes
> due
> >to hull geometry,
> angle of roll and how far the vessel is submerged) and this
> >plane is the metacentric height, which is a measure of stability for that
> >particular angle of roll. Large metacentric heights indicate a "stiff"
> vessel,
> >which has lots of stability but may not be quite as comfortable in a sea as
> a
> >"soft" vessel with less (but still sufficient) stability. A cylinder lying
> in
> >the water has exactly zero stability since CB and CG are always in a
> vertical line.
> >
> >-Sean
> >
> >
> >Quoting Joseph Perkel <joeperkel@hotmail.com>:
> >
> > >
> > > Gentlemen,
> > >
> > > I seem to keep coming back to this particular solution, probably because
> as a
> > > mechanical guy...I can figure out how to build this. As a pilot, I can
> > > visualize CG, W&B and forces at work, but
> what I am not......is an engineer.
> > >
> > > That lack of knowledge and my desire to build a successful and uniquely
> > > spectacular project, is partly the impetus to pursue Naval
> Architecture,....
> > > but I am not there yet. I do not yet know how to calculate for surface
> > > stability of floating bodies, but I do have an idea of what's required.
> > >
> > > the link below is in case the photo won't load
> > >
> > > http://www.frappr.com/?a=viewphoto&id=269116&pid=3198712&myphotos=1
> > >
> > > My post to Rick about width is what it is.....a guess. Would this be
> unstable
> > > at 8.5' ???, the key is in the math. Somewhere in here is the answer to
> this
> > > particular option. I'll let Jay speak to the sea sled option as it's
> beyond
> > > my ability to envision
> it.
> > >
> > > Thanks to everyone for the participation, the results are self evident.
> > >
> > > Joe
> >
> >
> >
> >
> >
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