RES: [PSUBS-MAILIST] Ambient pressure design considerations

["Jorge Lourenço Jr." <jorloujr@uol.com.br>]

Hi, Dave !

Being a hard-core full time lurker myself I'll dare this time to disclose MY
deep ignorance, following your (good !) example:

I think that there is no point building a sub where you are wet and wearing
a mask (yeah, I recall your saying DRY, but I'd bet it's gonna be a semi-dry
vehicle due to ballasting issues...). The only justifiable thing I can see
in this approach is  the protection against some environmental hazards
(sharks ?). We'd be better off diving donning the regular diving gear and
being pulled by a scuba tow. That means a lot of speed, greatly extended
bottom time and unsurpassable freedom of movement. And a lot cheaper, let's
not forget ...

If I ever build an ambient dry submersible I'll mimic the SportSub [
http://www.ivccorp.com/ssinfo.html ] and the Markham Wing [
http://www.psubs.org/pic/wet.html ] designs, for instance.

The SportSub features a continous flow air feeding device that sweeps away
the stale air and besides that has the advantage of providing a rebreathing
effect that circumvents the oxygen waste of a scuba (open circuit) gear
extending bottom time about four times. This is not to be despised. By the
way, CO2 buildup is not a concern, if you are not diving for hours, even in
the K-250, where the breathing air is what is entrapped inside the hull when
the hatch is closed, and moisture condensation will happen anyway, requiring
more than fresh air to be avoided.

The Markham Wing has a simple pipe pivoting around its elbow to set the
water level inside the "cabin" thus controling the buoyancy.

Both devices are very simple, easy to build and operate, reliable and cheap,
fully adhering to the K.I.S.S. principle, leaving little to be desired.

That's it for now, hope it helps...

Jorge L.


>
> Okay, I've silently observed this list for some time now and I'm ready
> to disclose some of my ignorance to the group in the hope of gaining
> some valuable input.
>
> My intent is to build a small ambient pressure dry sub for
> recreational use in the fresh water lakes of my area.  The conceptual
> design would be limited (by pressure switch) to a depth of 33 feet
> (aproximately).  I need to keep the sub as small and hydrodynamic as
> possible to minimize power requirements.  The sub will remain slightly
> positive in boyancy and will power-dive using dive planes which will
> be linked via a mechanical mixer to provide both pitch and roll
> control.  A control stick and rudder pedals would be incorporated as
> in an airplane (like flying under water).  If the craft exceeds the
> depth of 33 feet the pressure switch will deactivate the motor thereby
> forcing it to ascend back into its window of operation.  An emergency
> override switch will allow the use of power beyond the 33 ft. limit.
> My plan is to breathe compressed air through a two-stage regulator
> (scuba) with an exhaust duct to carry exhaled gasses to the outside of
> the sub.
>
> Any red flags yet?
>
> By exhausting the exhaled air to the outside I hope to minimize
> moisture condensate and CO2 buildup inside the sub, however, I realize
> in order for this to work it is absolutely essential that the air
> pressure inside the sub remain ambient to the pressure outside the
> sub.
>
> I have to go for now, but I have more questions relative to ambient
> pressure and boyancy to come in another post.  I'm not looking for
> ridicule, but if you have some constructive criticism or see cause for
> concern with my plans thus far, I would value your input.
>
> Thanks,
>
> Dave Altis> Dave Altis schrieb:
>
> Okay, I've silently observed this list for some time now and I'm ready
> to disclose some of my ignorance to the group in the hope of gaining
> some valuable input.
>
> My intent is to build a small ambient pressure dry sub for
> recreational use in the fresh water lakes of my area.  The conceptual
> design would be limited (by pressure switch) to a depth of 33 feet
> (aproximately).  I need to keep the sub as small and hydrodynamic as
> possible to minimize power requirements.  The sub will remain slightly
> positive in boyancy and will power-dive using dive planes which will
> be linked via a mechanical mixer to provide both pitch and roll
> control.  A control stick and rudder pedals would be incorporated as
> in an airplane (like flying under water).  If the craft exceeds the
> depth of 33 feet the pressure switch will deactivate the motor thereby
> forcing it to ascend back into its window of operation.  An emergency
> override switch will allow the use of power beyond the 33 ft. limit.
> My plan is to breathe compressed air through a two-stage regulator
> (scuba) with an exhaust duct to carry exhaled gasses to the outside of
> the sub.
>
> Any red flags yet?
>
> By exhausting the exhaled air to the outside I hope to minimize
> moisture condensate and CO2 buildup inside the sub, however, I realize
> in order for this to work it is absolutely essential that the air
> pressure inside the sub remain ambient to the pressure outside the
> sub.
>
> I have to go for now, but I have more questions relative to ambient
> pressure and boyancy to come in another post.  I'm not looking for
> ridicule, but if you have some constructive criticism or see cause for
> concern with my plans thus far, I would value your input.
>
> Thanks,
>
> Dave Altis
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