Re: Mathematics for sub desginers (beginners)

["Alan D. Secor" <secor@btv.ibm.com>]

Ummmm, how can sea water be *less* dense than fresh water when it is
essentially fresh water with the addition of salt.  This would make it
*more dense*.

As a result,  33fsw=1atm=14.7psi=34ffw.

      ~33 fsw (feet sea water) ~= 34 ffw (feet fresh water).

You might want to double check your scuba books!

Regards......Al Secor (Scuba Instructor SSI DCSI5598).

>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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--
Alan D. Secor
e-mail: secor@btv.ibm.com