[PSUBS-MAILIST] Terminating a conical transition

[Sean T. Stevenson via Personal_Submersibles]

Joe - a couple of things:

1)  Free-flooding compartments still contribute to the vessel's overall
inertia and consequential power requirement.  Whether you are moving
usable internal space, or an oddly shaped slug of seawater, the
effective density of the volume is the same when submerged.  The only
difference would be the crane weight out of the water when the
free-flooding spaces have drained.  Thus, it behooves the designer to
maximize the useful internal volume of the pressure boundary, or to
minimize the total displacement volume of the vessel for a given
pressure boundary volume.  In other words, you want to eliminate
free-flooding volume where you can, and looking at your design, I see
the opportunity to add conical sections to each end of the cylinder, and
then use smaller hemispherical heads at the end of each cone (thus
creating a high volume pressure boundary with more usable internal
space), or alternatively, shortening the length of the superstructure /
fairing assembly to minimize the overall displacement and unnecessary
free-flooding volume.  The latter solution would, of course, minimize
the total displacement and dead weight of the completed vessel.

2)  Dive tank # 1 and #2 : I presume that these are your main ballast
tanks for dive vs. surface operation?  I would give a little more
thought to stability here.  It seems more advantageous to have your
ballast tank volumes above the vessel CG wherever possible.  In the
surfaced condition, the hull form works the same way as a boat hull in
providing increased righting moment with angle of roll (provided the
hull isn't cylindrical).  Completely submerged, you have only the
difference between your center of buoyancy and center of mass to offer
righting moment.  The transition between surfaced condition (MBTs blown)
and submerged condition (MBTs full) can be dangerous as your metacentric
height can be eliminated before the CB/CG righting moment is established
on submersion.  Ideally, your CB would be above your CG regardless of
operating condition, in which case your vessel is always stable, and the
hull form buoyancy only acts to stiffen the vessel in the surfaced
condition.

Sean


On 2014-05-04 13:07, Joe Perkel via Personal_Submersibles wrote:
> I've incorporated some of the suggestions in the attached drawing.
> Still, I've got a lot to think about here but I am also excited about
> the possibilities and the potential outcome. This image should give
> some idea of what's on my mind. What you see is the water ballast
> arrangement on the original Seehund, and how my proposed pressure
> boundary fits into this scaled down version. The following is a list
> of concerns and or design considerations.
>
> 1) Clearly, I have no need to compensate for the loss of torpedoes
>
> 2) New pressure boundary provides for massive MBT volumes (/Low
> pressure compressor to blow down volumes/)
>
> 3) Torpedo battery pods may need to incorporate some free flooding
> spaces to reduce weight, or perhaps reduce battery capacity to a
> single pod in lieu of the former forward water ballast tank, then
> completely free flood both torpedoes completely??. (/Boat will
> incorporate a gen-set/)
>
> 4) Questionable reliability of external motor pod assembly.
>
> 5) Stability considerations
>
> Thanks for the input gents, It really helps me to take a step back on
> occasion!
>
> Joe
>

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