[PSUBS-MAILIST] Stability & Buoyancy

[Marc de Piolenc]

Reserve buoyancy doesn't necessarily resist heave. The greater the rate 
of change of buoyancy with immersion (dependent on waterline area for 
rate and on reserve flotation volume for limit), the stronger the 
coupling to waves. If the boat's natural heave frequency is far 
different from the wave frequency, no problem. If they resonate, you 
could feel like a fishing float in a strong chop!

Marc

On 11/30/2013 8:10 PM, Joe Perkel wrote:

> Incidentally, reserve buoyancy defined as that which is above the
> waterline. Such buoyancy comes into play for walking on deck and more
> importantly to oppose / resist heave.
>
> ------------------------------------------------------------------------
> *From: * Joe Perkel <josephperkel at yahoo.com>;
> *To: * personal_submersibles at psubs.org <personal_submersibles at psubs.org>;
> *Subject: * Re: [PSUBS-MAILIST] Stability & Buoyancy
> *Sent: * Sat, Nov 30, 2013 11:49:29 AM
>
> 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 <http://overview.mail.yahoo.com?.src=iOS>
>
>
> ------------------------------------------------------------------------
> *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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