Need some help with a depth and time

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landonnin1

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Scuba Instructor
Messages
72
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Location
Michigan
# of dives
1000 - 2499
I just built a pressure vessel to test underwater camera housing I am able to test to 300 psig or about 673.46 fsw. I am thinking of only going for 450 fsw guarantee but I would like to know if any one could tell me about how long of dive would a tek be on at this depth. this is not for a commercial dive.the reason I ask is so I can leave the housing at that pressure for about one complete dive.Now I know this could depend on one consumption of the mix in the tank but all I am looking for in a general number or any help I would be thank you even if some one could give me the math to figure this out I would do it

thank you for reading this and any help you can offer
Matt Landon DM
 
I cant imagine that time at depth would matter. For example, submarines are rated for an operating depth and a crush depth. The submarine can operate at operating depth for a virtual indefinite period of time. So, if your housing will survive 300fsw for 30 minutes, I would guess it will survive that depth forever (or at least a long time). As far as time is concerned at such depths, you are talking about a saturation dive if the time is long. I suppose you could stay at 300fsw for a very long time, gas allowing. You would be saturated and subject to significant decompression/offgassing routines. In my mind this would have no effect on a housing certified to withstand 300fsw.
 
Not really sure what a "Tek" is, but if your talking about deep diving its gonna depend on how the user is set up ie CCR or OC. Just as a rule of thumb someone on OC can only pack about 260cuft of gas and is using the rule of 1/3's so they will only go thru about 172cuft of gas before they turn the dive. At A SAC rate of .4 which is about 4cuft @ 300' translates into about 43 minutes at depth with a bunch of deco on the accent. Anyways your not going to find a whole bunch of ppl on CCR or OC staying deep for very long unless your talking about saturation diving. Hope that helps a little.
 
you make a good point thank you very much this is a good answer to my question

thank you for taking the time to read my post and replying
Matt Landon DM
 
Not really sure what a "Tek" is, but if your talking about deep diving its gonna depend on how the user is set up ie CCR or OC. Just as a rule of thumb someone on OC can only pack about 260cuft of gas and is using the rule of 1/3's so they will only go thru about 172cuft of gas before they turn the dive. At A SAC rate of .4 which is about 4cuft @ 300' translates into about 43 minutes at depth with a bunch of deco on the accent. Anyways your not going to find a whole bunch of ppl on CCR or OC staying deep for very long unless your talking about saturation diving. Hope that helps a little.

All I can say is...wow!:confused: I sure hope you're not doing 300' OC dives.
 
Not really sure what a "Tek" is, but if your talking about deep diving its gonna depend on how the user is set up ie CCR or OC. Just as a rule of thumb someone on OC can only pack about 260cuft of gas and is using the rule of 1/3's so they will only go thru about 172cuft of gas before they turn the dive. At A SAC rate of .4 which is about 4cuft @ 300' translates into about 43 minutes at depth with a bunch of deco on the accent. Anyways your not going to find a whole bunch of ppl on CCR or OC staying deep for very long unless your talking about saturation diving. Hope that helps a little.

Why is my math wrong? haha

Just a little.

In a set of doubles I carry ~300 cft of backgas.

Rule of thirds on 260 cft means turning the dive with 172 remaining, not going through 172 before turning.

Sac rate of .4 is pretty damn good and I don't know of many people doing 43 minutes of bottom time at 300', CCR or not.
 
The time you need to keep something pressurized too is more a function of what you are using for leak detection. For a 450ft rating you probably want to pressurize to 600ft for a few minutes. Mostly a CYA
 
The time you need to keep something pressurized too is more a function of what you are using for leak detection. For a 450ft rating you probably want to pressurize to 600ft for a few minutes. Mostly a CYA

Ditto what rjack said. Having a housing that handles the the static pressure of a certain depth doesn't necessarily mean it will fare well under the dynamic concerns of moving through the water, bumping around, etc. Adding a safety factor to your tests would seem prudent.
 
Just a little.

In a set of doubles I carry ~300 cft of backgas.

Rule of thirds on 260 cft means turning the dive with 172 remaining, not going through 172 before turning.

Sac rate of .4 is pretty damn good and I don't know of many people doing 43 minutes of bottom time at 300', CCR or not.

Ahh yes, the difference being cave diving and open water diving. Since we are not in an overhead environment (actually since its deco it would be) thats when we turn and deco is done on the way back. Cave fills also helpful but not everyone does them.
 
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https://www.shearwater.com/products/perdix-ai/
http://cavediveflorida.com/Rum_House.htm

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