Re: [PSUBS-MAILIST] Isn't 'Mini book review.' anymore--pressure t est

[AndrePevestorf@aol.com]

In einer eMail vom 13.04.2002 15:57:49 (MEZ) - Mitteleurop. Sommerze schreibt machine@epix.net:


> But it's not pressure that is detected this way. 
> To use this method properly to detect the end of the elastic limit on a sub hull, 
> you read the volume of fluid expelled from the interior of the sub as the sub is being squeezed in the test chamber.  They are related, but it's easy to detect very minor changes in the subs over all volume using this method.  Accuracy is a matter of the diameter of the vessel your reading the expelled fluid in.  For only a few thousants of an inch reduction is the sub's diameter there is a great difference in the fluid level in a small graduated tube.  When monitoring pressure with in the sub, the pressure gauge only reads the pressure of the chamber.  It's one in the same!  Some fluid must be allowed to escape from the interior of the hull to allow the sub to compress or your not actually putting forces on the hull. From what I read, this method was used by Perry Submarine Company in Florida at one time. Dan H. 


Hi Dan,

You are absolutely right ans I completely agree with you.
Thats the way you have to do it in a test chamber. 

But I thought about to adapt this method to a free sink test under outdoor conditions!

Then I guess you wouldnīt float your sub completely with water, would you?
Then it is air in the interior of the sub and then a fine pressure gauge will detect the very small increase of air pressure due to the squeezed hull.

Do you have an other suggestion how to do that? 

It is brilliant to use incompressible water to measure the volume reduction in the hull and to zoom this effect by using a small tube as an indicator.
But lets say you fill the sub with water (add some extra bouyancy only for the test outside the hull) -- how do you want to read the measuring tube???  If there is a long hose to the surface then the water column in the hose is from the same hight as the sub is deep and nothing will happen.....

A compromise could be to fill not the entire sub with water. The remaining air bubble is reduced and the absolute pressure increase is higher due to the hull shrinking.
If you have only the pressure hull without any fittings and without any extra ballast ...hmmm ...I believe this could be work as well. 

The displacement of the closed hull minus itīs own weight gives the needed extra ballast to sink the hull. If you put 2/3 of this ballast as water into the hull and the remaining 1/3 as additional drop weight..... hmm sounds strange but it works as long as no extra leak will appear... AND great advantage... you sacrifice less drop weight!!!

But then make nails with heads:
Organise two big bouys made from a hard stuff (hard foam, foamed tubes or what ever) ... better test this bouys seperate in a first deep sinking test ...
Then attach the sub hull between the bouys (make it very carefull) and fill the hull with water. Let a small remaining air space (lets say 5 %) and install the electric pressure indicator) seal the hull, add the drop weight and say "good by hope Iīll see you again.."
Control the deep with the rope (Do you have tie the sub, didnīt you?) and read the value from the pressure indicator.

The gread advantage of this elaborate procedure is that it takes no matter if the hull becomes leak...only 5% are remaining to float and after releasing the drop weight you get you hull back.

Unfortunately this seems to be applicable only to small pressure hulls otherwise you will need quite a hell of extra bouyancy indeed!

Heh folks !!!  flash-idea alert !!!

We could do it like the TRIESTE !!!  put all your fuel oil tanks out of your homes and let them swim... cheap plastic tanks filled with fuel... hehe thatīs it......  (could be an environment problem indeed)

Nevertheless It seems to be more worth to think about a relatively simple "sinkable test dock" than to build a personal test chamber .

Such a "sink dock" should looks like a common swim dock exept that the bouyancy chambers are not floatable.

Or for more shallow test deeps make the dock with ambivalent air filled swim chambers ... needs only an old scuba gear some scuba tanks and some softtanks made from thin sheet metal. 

Or buy an old pontoon from the army...

It should looks like this:

X-----------------------------X
I                              I  <------- swim chamber (if you use a single pontoon)
I                              I
X-----------------------------X
 \                            /
  \                         /     <---- girders
    \                      /
      \                   /
      ===========    <--- platform for the hull 
                I
             OOO           <---- some extra weight for stability or as emergency drop weight


OR:


X---------X                              X---------X
I           I                              I           I          <------- swim chambers
I           I                              I           I
X---------X                              X---------X
             \                            /
               ==============    <--- platform for the hull 
                           I
                        OOO           <---- some extra weight for stability or as emergency drop weight


A.