[PSUBS-MAILIST] Stability & Buoyancy

Sat Nov 30 10:01:47 EST 2013

The Navy training film on youtube I linked to earlier is from 1955 and not from WW2.  Here's a good, brief article of historical development of saddle tanks on military subs.  Since the mid-1950s most military subs have had their ballast tanks inside the pressure hull.  http://en.wikipedia.org/wiki/Saddle_tank_(submarine)

Surprisingly the ballast tanks on WW1 German subs were low inside the pressure hull with flat tops.  This sometimes presented problems when the crew needed to blow at depth.  

Jim

-----Original Message-----
From: Joe Perkel <josephperkel at yahoo.com>
To: personal_submersibles <personal_submersibles at psubs.org>
Sent: Sat, Nov 30, 2013 5:50 am
Subject: Re: [PSUBS-MAILIST] Stability & Buoyancy

BTW Alan, that document you stumbled upon is an excerpt from the NAVPERS 16180 Fleet Type Submarine manual from WW2. I have had a copy of this on CD for years and this manual while chock full of interesting and informative stuff, it has been the single biggest influence on me with regards to an upward design spiral. 

Stop reading it, it's pure evil! )

Joe

Sent from Yahoo Mail for iPad

                                                            From:                                                        MerlinSub at t-online.de <MerlinSub at t-online.de>;                            
                                                            To:                                                        Personal Submersibles General Discussion <personal_submersibles at psubs.org>;                                                                                                     
                                                            Subject:                                                        Re: [PSUBS-MAILIST] Stability & Buoyancy                            
                                                            Sent:                                                        Sat, Nov 30, 2013 10:51:00 AM                            

Hi Alan, 

additional the sub can dynamic unstable during surfacing.

There is a lot of water in the free flooding open sail.
If you surface fast and with to small opening in the 
bottom of the free flooding sail the extra weight can 
move the CG so high that the sub tends to get heavy 
side angles during surfacing until the water rush out. 

The picture 8382a shows the higher waterlevel during surfacing 
in the sail and the MBT sadlle tanks still under water 
but for this sub the extra weight was not critical.

But on a military one with there tons of 
water in the sail during a fast emergency surfacing 
it can be a problem. 

By the way Euronaut has no Kingston valve without any problem
and a positve GB alltimes greater than 2". 
On dive station or surfaced. 
And great openings in the bottom of the sail. 

Boats without Kingston valve tends to lost some 
bouancy during rough sea. The tanks and the seastage
work like a air pump and some water enter the tanks.

On the otherside a boat with Kingston and a 
compressed air blow out system can blow away the 
tanks very fast if you forget to open the Kingstons 
during blowing the tanks or have a air leak 
in the in the pipe to the tanks.

vbr Carsten 

"Alan James" <alanlindsayjames at yahoo.com> schrieb:

Hi everyone,
While reading through some background info for the G.L.
certification document, I came across this link with a good
explanation of stability & buoyancy
http://maritime.org/doc/fleetsub/chap5.htm

There is a phenomena described, where submarines can be 
unstable to the point of turning over during the transition from
surface to diving & vice versa.
This has to do with the centre of buoyancy moving upward past
the centre of gravity. As it approaches the centre of gravity the
submarine is at it's most vulnerable point.
This would be different for individual designs & a worry if
you dropped your emergency drop weight.
I had been told by a pilot that he never stuffed around while
descending & liked to drop as quick as he could.
I didn't have a full understanding of this & thought there may
be others in the same boat.
Regards Alan

-- 

Carsten Standfuß
Dipl.Ing.Schiffbau @ Meerestechnik
Heinrich Reck Str.12A
18211 Admannshagen

0172 8464 420
WWW.Euronaut.org
Carsten at euronaut.org

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