Need cylinder size information for a wet sub

[Liz_2008]

Hi,

I am doing a design project as part of my mechanical engineering degree at university. It is to design a leisure submarine type vehicle that will operate at 10 m for 1 hour. I have decided to go for an open vehicle which means I will need scuba tanks for our air supply. I was wondering if anyone could suggest a tank size that I could use. The power for the sub is by means of pedal power so quite a lot of energy and therefore air will be required. Any help asap would be greatly appreciated.

Liz.

 

[roakey]

Use the search function and look for "SAC" and "SCR" which stands for "Surface air consumption" and "Surface consumption rate."

This is typically expressed in cubic feet per minute at 1 ATA (surface pressure). You're talking about 2ATA. A nice round number for a normal experienced diver swimming around is a SAC of .5.

At 10M you're at about 2ATA.

So assuming that the amount of effort is the same as swimming, at 2 ATA that'll be 1 cf/min, which means that an AL80 will last 80min if you empty it, or a little more than an hour if you surface with 500 psi remaining.

If it takes a lot of effort to pedal your sub, up that SAC to 1 or 2, and you'll need some pretty large cylinders.

Roak

 

[Epinephelus]

You say "we." Does that mean a two person sub? My guesstimate is that if you're peddling you'll probably burn about 2 SCFM per person at 10M, so you'll need a minimum of 120 SCFM/HR/person. With a reserve I'd up that to 160/HR/person, or basically two standard 80's for a one person sub or four for a two person sub.
Have fun, and let us know how it works out.
E. itajara