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Re: [PSUBS-MAILIST] Ambient running on nitrox



Hi David,
I'm not an expert on domes. I read the relevant parts in the Stachiw book & Brent has sent me a lot of diagrams wich I'll forward to you.
I have a 500mm dome 10mm thick, a 500mm dome 3mm thick & are getting a 500mm x 25mm thick blown dome made up. I may end
up with 2 x 25mm thick blown domes as the guy making it was't 100% happy with his first attempt.
I am having the flange trimmed to 10mm & mounting it in a block of acrylic & fiberglass. Then attaching my closure mechanism & hinges
directly to this. I have done a bit of mold making, casting & fiberglassing in the past, so thats why I'm going the way I am.
With the 10mm area of flange keyed into the fiberglass the dome won't lift off wich is a problem in shallow water. The block of acrylic /  
fiberglass will also support the inner bend of the flange wich is a weakness.
Anyway I'll be able to test this out a bit with all these domes.
I've been going 1atm, ambient, 1atm, ambient, 1atm over the last year. I don't think its a lot cheaper going ambient. My 25mm thick blown
dome is costing $1000- NZ this should be good for operating to 250ft. The 10mm thick dome cost $128- NZ.
Like you I'm building to a budget, fortunately I'm not married anymore so can happily throw what little money I do have at the sub without
being made to feel severely guilty.
Can relate to the need to do something practical on this project. There is so much reading / research to do & its good to do something
practical that makes you feel you're progressing. Will send those diagrams off site.
Alan
 
----- Original Message -----
Sent: Tuesday, August 18, 2009 7:33 PM
Subject: RE: [PSUBS-MAILIST] Ambient running on nitrox

Alan,
 
   I see my ambient as a stepping stone. I would much rather make an ambient than perhaps never make a sub at all.
   My compass would work in an ambient!
   How big is your acrylic dome and does it have a retaining lip built on? I am having trouble seeing how to deploy the one I have at resent.
 
                                                                                                         David Bartsch
 
 

From: alanjames@xtra.co.nz
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Ambient running on nitrox
Date: Thu, 13 Aug 2009 15:24:57 +1200

Hi Jay, Thanks again,
The ambient sub is now dead & buried. I'm considering using my acrylic dome as a gold fish bowl.
Had done research on oxygen toxicity & was aware of my parameters to avoid central nervous system
toxicity & pulmonary & ocular toxicity. I was intending to have O2 monitoring but  as you advised, they
can be suseptable to moisture & in an ambient there is more of that.
As said, the main flaw in this plan was the fact that When you got in, it would have a normal O2 concentration
& so if you cruised under the surface you'd  very quickly deplete your O2, with no nitrox comming in.
Also the fire danger.
It's great to be able to submit these ideas & have them critiqued. I thought I was on to a winner there.
Regards Alan
 
 
----- Original Message -----
Sent: Thursday, August 13, 2009 11:38 AM
Subject: RE: [PSUBS-MAILIST] Ambient running on nitrox

Alan,

Your ambient sub will definitely be unique and have several complications that are not encountered in a typical ambient PSUB.  You are going against convention in the technical diving community in that for all practical purposes you will have a rebreather without a means to monitor your oxygen levels.  You have much more to worry about than just fire.  While I admire your computations, I do not believe that they are as straight forward as you lay out.  In reality, when you look at your proposed life support system, it would be termed a feed-and-bleed case and these are governed by a differential equation vice a linear decrease in the oxygen level.  As it has been many years since I have had to contemplate this particular type of equation used in this manner, I will leave it to you to conduct further mathematical research. 

 

You should do a literature search on Dr. Bill Hamilton and oxygen tolerance.  The onset of oxygen toxicity can be rapid, with little forewarning, and have tragic results.  There are two types of oxygen toxicity, one due to high partial pressures at depth and the other due to length of exposure.  And since most ambient subs involve some parts of the body being immersed in water, you need to take in to account thermal exposure.  Something many people do not consider is that an exposure to 72 degree Fahrenheit water for an hour will put most people mildly hypothermic…with this comes a significant decrease in mental acuity and muscle strength.  Don’t remember where you plan on operating but exposure can be a significant factor.

R/Jay

 

 

Resepectfully,

Jay K. Jeffries

Andros Is., Bahamas

 

Save the whales, collect the whole set.

 

 

 

From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Alan James
Sent: Tuesday, August 11, 2009 10:30 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] Ambient running on nitrox

 

Thanks for your reply Jay these emails can take some time.

Thought I had you on the regulator issue.

As said on my initial post, I'd have to think on restricting myself to the dive time tables for air & the dive depth for nitrox as there would be a dilution of the O2 content.

However at say 99ft the O2 in a hull with an air volume of 200 liters would be 312 liters with a 39% nitrox mix. This would give me 144 liters of O2 before I

got down to the 21% O2 mark. This is  9.6 hrs at .25 liters per minute consumption. Not to mention the air at 39% O2 replacing it to keep the sub ambient.

Quite a safety margin seeing I'm restricted to decompression times. Also no need for a dedicated O2 feed.

I'll be using a scrubber & for the ambient system, a pipe open to the sea, comming up through the hull with probes down it leading to a solenoid valve.

As the water level increases it hits the probes wich activate the solenoid valve letting air in to equalize. Excess pressure bubbles out the pipe.

Like a dive, it will need planning & building in margins of error.

My main concern that I'll look into at depth is the fire risk.

Thanks for the shared experience of the moisture vulnerable O2 monitors.

I won't be trusting one with my life.

Alan

 



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