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<div><font size="3" style="background-color: transparent;">Joe,</font></div>
<div><font size="3"></font> </div>
<div><font size="3">That brings up another design standard. If everything except the pressure hull itself floods, the release of the drop weight must result in positive buoyancy. So if both battery pods and all ballast tanks flood, you should still be able to surface by releasing the drop weight. If the drop weight also sticks, you're screwed!</font></div>
<div><font size="3"></font> </div>
<div><font size="3">Jim</font></div>
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<div style="color: black; font-family: arial,helvetica; font-size: 10pt;">-----Original Message-----<br>
From: Joe Perkel <josephperkel@yahoo.com><br>
To: personal_submersibles <personal_submersibles@psubs.org><br>
Sent: Fri, Nov 29, 2013 10:27 pm<br>
Subject: Re: [PSUBS-MAILIST] Stability & Buoyancy<br>
<br>
<div id="AOLMsgPart_2_7acb4649-e0cc-4657-8a53-23089ef17dca">
<table border="0" cellspacing="0" cellpadding="0"><tbody><tr><td valign="top">This issue, explains the existence of the snorkel in the K-350. Imagine for a moment, the loss of a MBT, or the flooding of a battery pod.<br>
<br>
I tell you, a lot of thought went into this little boat. Every time I look to exceed the parameters, I see better the original intent. Every time!<br>
<br>
Joe<a href="http://overview.mail.yahoo.com?.src=iOS" target="_blank"><br>
<br>
Sent from Yahoo Mail for iPad</a></td></tr></tbody></table>
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<b>
<span style="font-weight: bold;">From:</span>
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<a href="mailto:jimtoddpsub@aol.com">jimtoddpsub@aol.com</a> <<a href="mailto:jimtoddpsub@aol.com">jimtoddpsub@aol.com</a>>; <br>
<b>
<span style="font-weight: bold;">To:</span>
</b>
<<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>>; <br>
<b>
<span style="font-weight: bold;">Subject:</span>
</b>
Re: [PSUBS-MAILIST] Stability & Buoyancy <br>
<b>
<span style="font-weight: bold;">Sent:</span>
</b>
Sat, Nov 30, 2013 3:45:36 AM <br>
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<div><font size="3">Yeah, Jon, the concept of a keel tank seems a bit spooky. Trim tanks are often at the bottom of the boat but not below it, and their function has more to do with trim weight than with buoyancy. </font></div>
<div><font size="3"></font> </div>
<div><font size="3">To clarify what I said: "The lower your tanks, the greater your freeboard, but less CB/CG spread." That's true when the tanks are intersecting the water line. Once they are completely below the water line, moving them any lower isn't going to give you more freeboard, but it will lower your CB. Not good.</font></div>
<div><font size="3"></font> </div>
<div><font size="3">Jim</font></div>
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<div style="color: black; font-family: arial, helvetica; font-size: 10pt;">-----Original Message-----<br clear="none">
From: Jon Wallace <<a href="mailto:jonw@psubs.org">jonw@psubs.org</a>><br clear="none">
To: Personal Submersibles General Discussion <<a href="mailto:personal_submersibles@psubs.org">personal_submersibles@psubs.org</a>><br clear="none">
Sent: Fri, Nov 29, 2013 9:10 pm<br clear="none">
Subject: Re: [PSUBS-MAILIST] Stability & Buoyancy<br clear="none">
<br clear="none">
<div class="yqt0774515366" id="yqt75725">
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I'm somewhat a novice with CG and CB but it does occur to me that
the illustration in the document shows a circumferential ballast
tank which from the perspective of CB must be the worst type to
employ. The K-350 design with both drop weight and battery
compartments well below the ballast tanks provide an extremely low
CG with CB well above it at all times. <br clear="none">
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On 11/29/2013 9:54 PM, <a class="moz-txt-link-abbreviated" rel="nofollow" shape="rect">jimtoddpsub@aol.com</a> wrote:<br clear="none">
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<div><font size="3" style="background-color: transparent;">Hi
Alan,</font></div>
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<div><font size="3">Re: "the centre of buoyancy moving upward
past the centre of gravity... " This implies that somehow
the centre of buoyancy had been <em>below</em> the centre
of gravity which would be really, really scary. The ABS
rule (per Cliff's spreadsheet) is that the CB must be at
least 2" <em>above</em> the CG when the sub is submerged.
In the event the drop weight is released, the CB must still
be at least 1" above the CG. Frankly, that narrow a spread
doesn't meet my comfort zone.</font></div>
<div> </div>
<div><font size="3">When the sub is surfaced, any portion above
the water line is now dead weight since it is no longer
displacing any water. When that same portion was submerged
it was contributing buoyancy. Therefore the
above-the-water-line portion contributes to the CB moving
downward. Offsetting that is the fact that the main ballast
tanks were contributing little or no buoyancy to the extent
they were full of water when the sub was submerged. Once
they are filed with air they move the CB upward. If the
tanks are fore and aft as on the K-boats, they are located
even with the top of the cylindrical hull. However remember
that the portion of the ballast tanks now above the water
contributes no buoyancy. With the fore and aft tanks, the
tanks don't contribute much to lateral stability
(anti-roll); you're dependent on the CB/CG spread for
lateral stability. I'm purposely staying away from
any direct discussion of metacenter for now.</font></div>
<div> </div>
<div><font size="3">My MBT's are fore and aft. My original plan
for setting design procedures for adding saddle tanks was
this: Calculate where the surfaced water line would be <u><em>if</em></u>
I installed the saddles at 4:00 and 8:00 positions, then
actually install them higher so that the top of the saddles
would be right at the water line. This would give me
maximum lift and freeboard since no part of the saddles
would be above the water line. However Alec correctly
pointed out that having a portion of the saddles above the
water line contributes to anti-roll since the down-rolling
tank would then provide extra displacement and buoyancy to
push that side back up (handy if someone steps on that side
of the sub<font face="Arial, Helvetica, sans-serif">).</font>
The lower your tanks, the greater your freeboard, but less
CB/CG spread. The higher your tanks, the greater your
surface stability, but you sacrifice freeboard. The design
challenge is finding the optimum level.</font></div>
<div> </div>
<div><font size="3">Jim</font></div>
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