[PSUBS-MAILIST] K-600 buoyancy mystery

Sat Jul 30 15:51:40 EDT 2022

 Hi Sean, thanks for doing a sanity test for me.  Yes, the diameter specification is I.D., and your calculator matches my calculation almost exactly which was 301.6 using a 2 inch skirt.  But I think Cliff is correct that a 36 inch elliptical head has a longer skirt (flange) and therefore provides even more buoyancy.  Regardless, my mistake was to deduct the weight of all the tank heads twice which caused my initial calculation of total buoyancy for the vessel to be much lower.
Love your software and I see you have updated it to include tank heads.  The one we have on the website is cylinders only.
Jon

    On Saturday, July 30, 2022 at 09:03:55 AM EDT, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Jon - If it helps, I ran weight and buoyancy calcs on one of the heads alone (per your description of 36" - I assumed ID because that is what head forming dies are based on, x 0.5625" wall thickness).  Straight flange length per ABS spec because my program didn't have a field to customize that.  Results in in-line image below. 

Sean

     ------- Original Message -------
 On Thursday, July 28th, 2022 at 12:35 PM, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

  Thank you Cliff, you got me back on track.  I was deducting the weight of the tank heads from their displacement which is unnecessary since I know the overall weight of the vessel from the CAT scales.  As such, all I need is the displacement of all the parts and then subtract the total known weight.  Also, I have been using 2 inch skirt on the tank heads which I think is correct for the battery pods but not for the main hull.  Recalculating the tank heads bring me to a total displacement of 4202 lbs which is definitely in the ball park that I would expect.
Jon

    On Thursday, July 28, 2022 at 01:09:26 PM EDT, Cliff Redus via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

  I modeled a K350 awhile back.  It has a similar hull to K600.  I think your displacement for the Main tank heads is wrong.  These are semielliptical heads with a 4" skirt. Displacement should be 5.96 cu ft per head x 62.4 ft^3 = 371.9 lbs per head for total of 743.8 lbs not 133 lbs.  This would bring your freshwater displacement numbers to 4,127lbs.
I think your battery pod displacements are low as well.  For K350, they are 442.5 lbs.  Also make sure you are adding displacement for any part that displaces water.  I am not sure you have accounted for all parts.

Below is the buoyancy table for the modified K350

| Buoyancy and Center of Buoyancy Database |  |
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Modified K350 hull that these calculations were made from.  36" OD x 72" Seam to Seam.

    On Thursday, July 28, 2022 at 10:45:03 AM CDT, Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 I'm stuck on a buoyancy issue with the K-600.  The operating and service manuals state that the working weight of the vessel (dive ready) is 4500 pounds less operator.  However, when I calculate the buoyancy of the vessel based upon it's physical dimensions I don't even come close to offsetting the projected weight as documented by Kittredge.  I know the stripped weight of the vessel is 3060 lbs, because I had it weighed at a CAT scale used by truckers which is suppose to be guaranteed accurate.
My buoyancy calcs (inches) and results in pounds are:Main hull - 36 x 72 = 2712.96Main tank heads - 36 x .5625 = 66.5 each = 133Conning Tower - 24 x 18 = 301.44Battery Pod - 12 x 45 = 188.4 each = 376.8Battery Pod Tank Heads - 12 x .365 = -1.83 each = -7.32
Total potential buoyancy comes out to 3516.88 lbs.  Deducting the 3060 known weight of the steel leaves 456 lbs of buoyancy however there is easily more than 456 lbs of machinery, electrical, and plumbing components that will be added to the stripped hull.  For example, Kittredge used 8 lead-acid batteries with a combined weight of approximately 320 lbs, 200 lbs from three 1-ATM motor containers, 150 lbs drop weight, and then operator weight would produce a combined total of about 800 lbs additional weight not including electrical, plumbing, and instrument components.
So from a weight perspective, 4000 to 4500 pounds sounds reasonable for a dive ready K-600.  But with only 3516 lbs of physical vessel buoyancy it would be 500 to 1000 pounds negatively buoyant which is obviously an impossible configuration.  Given that we know this submarine dived successfully, what am I doing wrong with my calculations?
Jon_______________________________________________
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