RE: Mathematics for sub desginers (beginners)

[Bear Woods <bearasaur@yahoo.com>]

The info was from memory.  
I do not have the scuba book on hand, so I'll look later.  I checked
several other sources.  You are correct...sea water is more dense than
fresh water.  I suspect I reversed the numbers by operating from
memory.  I hope this did not cause too much confusion.
Thanks for the correction.




---"Morrisson, Richard D" <Richard.Morrisson@PSS.Boeing.com> wrote:
>
> I don't know where you got the information that seawater is less
dense but I think you should re-check it!  The rule of thumb I
remember is 34' not 30' for freshwater.  Consider that seawater is
just regular water with a bunch of rock (salt) dissolved in it, which
makes it heavier for a given volume.
> > ----------
> > From: 	Bear Woods[SMTP:bearasaur@yahoo.com]
> > Sent: 	Thursday, February 18, 1999 12:45 PM
> > To: 	personal_submersibles@psubs.org
> > Subject: 	RE: Mathematics for sub desginers (beginners)
> > 
> > Good explanation.....but I have been operating under the assumption
> > that seawater is slightly less dense than fresh water.  From the
SCUBA
> > days ~33ft=1atm=14.7psi in sea water, ~30ft=1atm=14.7psi in fresh
> > water.  In the units below this means ~0.445psi/ft for seawater and
> > 0.49psi/ft for fresh water.  This means that given equal conditions,
> > the sub in fresh water is more bouyant than the one in sea water.  
> > 
> > 
> > 
> > 
> > ---"Morrisson, Richard D" <Richard.Morrisson@PSS.Boeing.com> wrote:
> > >
> > > For water pressure at depth consider a box 1' by 1' by whatever
> > tall.  The area on top of the box is therefore one square foot. 
Water
> > (sea) weighs about 64 pounds per cubic foot (fresh is about 62.4). 
> > The top of the box must support the weight of (pressure due to) the
> > water above it.  This weight is 64 times the depth in feet (the
pounds
> > per cubic foot times the height in feet).  Divide the resulting
pounds
> > per square foot by 144 to get psi.  It comes out to about .44psi per
> > foot.   Hopefully you can follow the logic to this explanation and
see
> > the basis for the formula, which is generally more valuable than the
> > formula itself.
> > > 
> > > > ----------
> > > > From: 	sebastian.hunt@virgin.net[SMTP:sebastian.hunt@virgin.net]
> > on behalf of Seb[SMTP:sebastian.hunt@virgin.net]
> > > > Sent: 	Thursday, February 18, 1999 8:15 AM
> > > > To: 	'personal_submersibles@psubs.org'
> > > > Subject: 	Mathematics for sub desginers (beginners)
> > > > 
> > > > Hi. Can anyone tell me where I can find out the formulas that
are
> > important for submarine design? Starting quite simple, I still can't
> > find the formula for water pressure at depth. I assume this would be
> > elementary physics, but I must have missed that day at school! What
> > about calculating thrust from a prop, given its
dimensions/pitch/speed
> > etc? My web searches have revealed nothing so far.
> > > > 
> > > > I'm also quite keen to track down information about human
> > tolerances to variations in air pressure and gas mixtures and
anything
> > else that might pose a physical threat to a sub pilot.
> > > > 
> > > > Hope someone can point me in the right direction.
> > > > 
> > > > Cheers,
> > > > 
> > > > Seb Hunt
> > > > 
> > > 
> > 
> > _________________________________________________________
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> > 
> 

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