[PSUBS-MAILIST] Mechanical Depth Gauges

Mon Jul 30 22:16:25 EDT 2018

Hi Doug! I looked on my laptop and sure enough found a simple 2D CAD file
called "Depth gauge faceplate." So here you go, I'll paste a screen shot
below so you can print it. It's black and white, and the red was I think
just done with a marker over the hatch pattern. Looking at this, the "250"
is not quite straight, but when printed at the scale of the instrument I
don't recall noticing it. So... just try printing this a few times until
you get the scale right, then cut out with scissors and then paste right
onto the instrument. That's all there is to it.

Concerning the question about whether the instrument sees water, here's an
explanation for everyone else. The pressure gauge is in the CT, high in the
boat, but the line that feeds it pressure comes into the hull at close to
the lowest point. It is open to the sea, and as you dive the air in the
line will of course compress. It will not, however, ever compress enough
that the sea water actually reaches the instrument. The gauge measures the
difference between inlet pressure and ambient, so the instrument case is
not sealed or it would establish a reference pressure. There is an opening
in the case in order to equalize pressure, and as I recall a little filter
element intended to keep dust out but let air through. It will let in cabin
humidity too, which in places like the keys probably means you'll print a
new paper face-plate from time to time.

Best,
Alec

On Mon, Jul 30, 2018 at 2:36 PM, Douglas Suhr via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Ah, I think you're right Jon... because the gauge plate would not be
> pressured anyway, huh. Never thought of that.
>
> No there was no gasket or anything, so I guess any moisture in the
> viewing portion of the gauge would just come from moisture inside the
> hull of the sub.
>
> And thank you for the pressures... not a huge difference but I suppose
> at deep depths it could work out to be somewhat of an error.
>
> I wonder how Alec printed such a nice looking label(?). ~ Doug
>
> On 7/30/18, Jon Wallace via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:
> > Fresh water: .433psi per footSalt water: .445 psi per foot
> > If there was no gasket sealing the acrylic/glass cover and bezel then
> it's
> > likely condensation caused the wrinkling of the label.
> > Jon
> >
> >       From: Douglas Suhr via Personal_Submersibles
> > <personal_submersibles at psubs.org>
> >  To: Personal Submersibles General Discussion
> > <personal_submersibles at psubs.org>
> >  Sent: Monday, July 30, 2018 1:16 PM
> >  Subject: [PSUBS-MAILIST] Mechanical Depth Gauges
> >
> > All, as you may've been aware, in late 2015 I purchased Snoopy (a
> > K-250) from Alec Smyth. Regrettably I have been quite neglectful of
> > performing much upkeep on the sub, save for keeping the batteries
> > topped off. My schedule is finally allowing me to spend some real time
> > working on the sub and getting to know the specifics of each system.
> >
> > As you can imagine, I've been bugging Alec with a question here and
> > there, but thought with this topic I should start a discussion here on
> > the list for the benefit of anyone else who might have questions /
> > curiosities about mechanical depth gauges.
> >
> > Snoopy's depth gauge is nice and large (about 5" in diameter) so it's
> > easy to read. Alec created a nice label for the gauge face which reads
> > from 0 to 300 (in feet) with the last fifty feet being marked in red
> > to indicate 'too deep.'
> >
> > Problem is, when I looked at the depth gauge the other day, I noticed
> > that the transparent cover plate on the gauge looked to be quite
> > opaque (to the point where I couldn't quite read the numbers or count
> > the hash marks). I assumed that there was some moisture trapped in the
> > gauge, causing the obscuration. I decided to remove the gauge from the
> > sub and open it up to let it dry out.
> >
> > After removing the gauge from the sub, I unscrewed three small screws
> > around the bezel and popped off the transparent cover plate. It was
> > only then that I realized the opaqueness was not caused by moisture
> > but a distortion in the clear plastic. The distortion (like super fine
> > scratches) appears to be on the outside of the cover, as though it was
> > cleaned by something that started to melt the plastic or was left out
> > in the sun too long. I don't think either of these explanations make
> > sense, but I'm puzzled as to what might have caused it. I might try to
> > buff / polish the plastic, or perhaps just replace it with glass.
> >
> > I think it's a good idea to stick a dive computer in viewing range of
> > a viewport for a depth reading, but I like the idea of having a
> > mechanical gauge in the sub as well. A couple of questions that come
> > to mind: what is the pressure variation between salt water and fresh
> > water? Also, although I didn't find moisture in the gauge, The label
> > on the face is wrinkled a bit as though it has seen moisture. Although
> > water should never actually reach the gauge, I can see how moisture
> > from the inlet tube could find its way up into the gauge body. Should
> > I be concerned about drying it out somehow after a dive (especially in
> > salt water)? If so, how should I go about it? ~ Doug S.
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> >
> >
> >
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