Re: [PSUBS-MAILIST] Ambient pressure design considerations

["Dave Altis" <dabe@fidnet.com>]

Hi Jorge,

Thanks for responding.  I could not agree more about having little use for a
semi-dry sub (I've seen no sharks in the lakes around here),  which is why I
wouldn't bother!  ( There are some rather large catfish though! )   I
understand the engineering challenges involved in ballasting and boyancy
control of an ambient sub and I understand Boyle's law,  but I also believe
I'm quite capable of overcoming these challenges and I believe I will.  If I
find I cannot, I'll build a 1 atm before I go with a wet sub.  I know
condensation will happen anyway, but I still feel like it will help if I'm
not breathing on the window I'm trying to look out of.  Thanks for pointing
me to the SportSub site, I found answers to a couple of questions there.

I fear I've given the wrong impression to several of the group by refering
to my "ignorance".  Please don't confuse this with a lack of intelligence.
I've accomplished a lot of difficult things that a lot of well-meaning
scoffers have said "can't be done".  The sub has been an ambition of mine
for many years, long before I knew of this group's existence.  One of my
greatest areas of caution underwater is entrapment, a friend of mine watched
his son die that way, the least thing I want to do is become entraped in my
own devices.  I'm just trying to cover all my bases here, learn from the
mistakes and experience of others, not become another statistic.  No, I
don't know it all.  That's where the "ignorance" comes in, but I intend to
learn all I can to make this as safe as it can be.  That's how I found this
group.

Thanks again,  (it did help!)

Dave Altis

----- Original Message -----
From: "Jorge Lourenço Jr." <jorloujr@uol.com.br>
To: <personal_submersibles@psubs.org>
Sent: Sunday, November 02, 2003 2:56 AM
Subject: RES: [PSUBS-MAILIST] Ambient pressure design considerations


>
> 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