Well then you just need to think that the drop weights are along the center of gravity when the submarine is being designed, so they don't contribute to the sub being either top heavy or bottom heavy. Then when the design is finished the drop weights can be moved to the bottom where they belong and you can be sure that the sub will not tip over without them. It's just a matter of design isn't it. You have to design the sub to stay upright without any dropweights. Alex On 03-Dec-2009 MerlinSub@t-online.de wrote: > An oversized dropweight will capzied the sub on the surface > with the weight drop and no stability calculation done before. > > vbr Carsten > > > "Benjamin Arie" <BenjaminArie@gmail.com> schrieb: >> An over-sized dropweight would assist the sub in surfacing even if entangled >> or snagged. >> >> -Benjamin Arie >> >> >> On Thu, Dec 3, 2009 at 1:44 PM, <vbra676539@aol.com> wrote: >> >> > Dean, >> > Why would your drop weight be so big? A 12" pod X 120" is roughly 7.85 >> > cubic feet of volume which would displace about 500 pounds. Your internal >> > volume (figuring schedule 40ish) would be about 6.9 cubic feet. If the >> > battery pack is 6X8" in cross section and 108" long, that's 3 cubic feet. >> > Subtract that from the internal volume of the pod and you've got just >> > under >> > 4 cubic feet of free space or 250# of seawater on a bad day. So, a 250# >> > dropweight would equalize your trim for a flooded pod and your normal trim >> > and fairwater system would get you home. Yes? No? >> > Vance >> > >> > >> > -----Original Message----- >> > From: Recon1st@aol.com >> > To: personal_submersibles@psubs.org >> > Sent: Thu, Dec 3, 2009 12:02 pm >> > Subject: Re: [PSUBS-MAILIST] Reserve buoyancy >> > >> > *Alan this is in the line of my thoughts. From the beginning, for my >> > purposes of * >> > *exploring Lake Superior, I need to cover large areas. Speed and endurance >> > are* >> > *required. This is the reason for me carrying 18- 85amp batteries in >> > external battery pods.* >> > *If I look at the volume of water in a full flood state the drop weights >> > to compensate* >> > *would be much heavier than I would like.* >> > ** >> > *A 6000 lb lift is only the extreme as this can be my overall weight. >> > Safety is for sure* >> > *not to be compromised, my skinny little butt on the line. I am just >> > thinking this could* >> > *be a solution. I don't feel that the hatch breaking the surface to allow >> > egress is needed* >> > *for an emergency situation when there is a surface support craft. With a >> > full 6000 lb +* >> > *lift capability.* >> > ** >> > *Dean* >> > >> > In a message dated 12/3/2009 1:22:13 A.M. Central Standard Time, >> > alanjames@xtra.co.nz writes: >> > >> > Hi Mark, >> > Re the large ballast tanks, another thought is that the larger they are >> > the more drag, & inertia due to them being filled with water while >> > submerged. I'm not sure how much of a problem or extra drain on the >> > batteries this would be. Someone with experience might like to comment >> > on that. >> > Alan >> > >> > ----- Original Message ----- >> > From: "F. Marc de Piolenc" <piolenc@archivale.com> >> > To: "Personal Submersibles" <personal_submersibles@psubs.org> >> > Sent: Thursday, December 03, 2009 7:00 PM >> > Subject: [PSUBS-MAILIST] Reserve buoyancy >> > >> > >> > > I've been silently following the tender/reserve buoyancy discussion. As >> > > my primary interest is in salvage rather than sightseeing, I have >> > > assumed from the beginning that any sub that I build or am involved in >> > > building will follow safety criteria more like those of cruising Naval >> > > submarines than research subs. But now, reading the report of the >> > > salvage of the Alvin by the US Navy, I see that the allowances for >> > > research subs are inadequate. >> > > >> > > Aluminaut was selected for the salvage op because she was the most >> > > autonomous and robust of the submersibles available. After her first >> > > dive, when she spent several hours trying to insert the lifting toggle >> > > in Alvin's hatch, she surfaced with her batteries exhausted. It proved >> > > to be impossible to recharge her at sea, because the main hatch had to >> > > be kept open to allow hydrogen to escape, and when it was left open she >> > > shipped water! She had to be towed to sheltered water for repairs and a >> > > recharge. This is all the more remarkable because Aluminaut is the most >> > > seamanlike of all the research submersibles that I've actually seen. >> > > >> > > Battery vented into the crew space? No means of airing the boat without >> > > leaving the hatch open? I can understand not providing a separate >> > > snorkel or air-induction trunk - this is a deep diver, and every >> > > pressure-hull penetration is a potential failure point - but in that >> > > case the saddle tanks should have been made larger and some means of >> > > fitting a funnel over the main hatch to prevent water ingress should >> > > have been provided. And as for venting the battery into the crew >> > > compartment, ANY arrangement is preferable to one that exposes the crew >> > > to hydrogen, or worse - chlorine! >> > > >> > > http://www.archive.org/details/recoveryofdeepre00unit >> > > >> > > I assume that reluctance to add saddle tank volume in a personal sub is >> > > due to the need to trailer it home. If it exceeds maximum highway specs >> > > it must obtain a special movement permit every time it hits the road. >> > > >> > > Best, >> > > Marc >> > > >> > > >> > > >> > > ************************************************************************ >> > > ************************************************************************ >> > > ************************************************************************ >> > > The personal submersibles mailing list complies with the US Federal >> > > CAN-SPAM Act of 2003. 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