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Platinum Member - I wish...
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Discussion Starter #1
I know this has been discussed previously and I'm pretty sure some of the responses to this thread will be buy a twinset, buy a rebreather and the normal stuff :D

I am currently diving <30m and looking to move into slightly deeper stuff maybe <40m using Nitrox in the future but thats about it for the next 2 years or so.

I dive would dive the low 20's without a personal redundant air supply, obviously my buddy's there if I needed to grab a reg, without really giving it much thought because the surface doesn't seem that far away.
Passed that, getting into the high 20's and 30m range it seems to be considerably deeper and such precautions should be taken as ascending directly to the surface may cause considerable problems. (Yes, I realise you still have your buddy but the likely hood of getting seperated is increased and also the danger if I couldn't get to them so i'll hope for the best, plan for the worst.) Hence, the idea of a reduant air supply would come in.

One option is a twinset (twin 7's came to mind) but I discarded that idea due to the increased inital purchase price, the fact that if you wanted to do dives you would need either another twinset of a HP decanting cylinder and also the fact my LDS charges double the amount to fill twin 7's compared to a single 15.

Next option:
Pony. A ally cylinder sideslung with enough air to get to the surface. Not used during a dive unless an emergancy could be used for many dives without a refill as the only gas you use is when you pressurize it at the start of the start and purge it at the end. Cost is only for the bottle and rigging seems reasonable. Now going with that option.

My SAC is around 19/20 on an average dive. In a situation arrising, needing the use of my pony that may have doubled, 40l a min then?

Running off the maximum depths I want this setup to be good to would be 40m. Before the ascent may be faffing around for a few mins sorting myself out so: (also means it adds some conservatism to gas plan)

5 bar * 40l/ min * 3 mins = 600lt's
Then ascent at 9m/min
40m / 9 = 4.5 minutes roughly
Gas used on ascent is average depth * time. Average depth is 20m, pressure then is 3 bar.
3 * 4.5mins * 40 = 540

Total gas required = 600 + 540 = 1140 litres
Presuming a decent fill of 230 bar then
1140 litres / 230 bar = 4.95 litres

So my pony cylinder would need to be 4.95 litres providing my maths is correct. Someone mind checking that?

That rules out the normal 3 litres pony, so leaves a 5.74lt or 7lt cylinder. Fine
The cylinder will be sideslung so something of that size will need to fit my BC.

Pony will go on my left side I think but I didn't have picture showing that side but they are setup exactly the same way.
No visible reasons why it couldn't be mounted there - Tick

So from my conclusions a 5.74lt or 7lt cylinder would be up for purpose. Now deciding between the two.

Cost - Not sure how much they differ not massively i'd presume
Size - This is where they could differ
Future Uses - If in a couple of years I were to progress my diving into deco, and twinsets which it may never do but hypothetically either size could be used as a stage.


So after you have read the post this far, and I congratulate for doing that, what would you draw the conclusion was the best to get? 5.74ltr or 7ltr? That is of course providing my working correct and isn't massively flawed.

I now wait your reponse,
Matty
 

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Go for an AL40 if you can find one. Ponies tend to spend their entire lives full, so a light cylinder like that won't tip you over and you won't even know it's there. They're also very easy to handle out of the water, so you won't find yourself deciding not to bother with the faff on the boat and then realising you need it underwater :)

If you are using a 7l as a pony you need a twinset, and not just a 7l twinset. Plus when it comes to deco diving you can use the AL40 as an O2 or 80% bottle and it will do you fine for most dives.

Digs.
 

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What size?

Well, in my opinion, for the deeper stuff you seem to be looking at in the future, a 7L alu cylinder would be what I'd be looking at.

Or maybe a 11L...

Personally, I dive with a 7L side slung and barely notice it's there.

Oh, but I'm on CCR...

:)
 

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The worlds slowest sailor.
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i dont see the point in taking down gas just to bring it up again.

maybe go for a larger stage and use some of it for the dive and some for reserve.

my favourite set up now for a single bcd/wing is an ali 80 stage -plenty of gas and plenty of options and great for travelling abroad.
 

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I used to dive 15l single happily down to 35/40m with a 3l pony "in case". No deco and generally around 45min dive time.
I would do 45/50m on reduced dive time.
50m + I used to carry a side slung 7l instead of the 3l, at this point I decided it was getting stupid and got a 2x12 twin set. The 58m free flow helped with this discision.
I used to have a sac on a dive of around 19~22, deco around 14.
Poo+fan interface moment in Dosthill worked out at around 90lpm SAC.
Assuming your SAC will only double is a little unrealistic.
I would rather have more gas than nearly enough, hence the YBOD when 2x12`s were no longer big enough.
 

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Gettin' busy with the fizzy..
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why not swap your 15ltr for a 12ltr then pick up another cheap 12ltr and use twin ind's get a set of buddy twining bands, plenty of air more stable and you will probly get 2 dives out of one fill
 

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those spare air's are great!!!
.
.
.
.
.
.
in the pool
And remember.............

Nobody has ever died whilst using one................

:D
 

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Platinum Member - I wish...
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Discussion Starter #14
Hem, Hem, bringing this thread slightly more on topic :D

Go for an AL40 if you can find one..
a 7L alu cylinder would be what I'd be looking at.
favourite set up now for a single bcd/wing is an ali 80 stage -plenty of gas
So thats one recommendation for a 5.5L, one for 7L and another for an 11.1L cylinder...tbh, that doesn't really help my decision but I think I will rule the 11.1L out for being just a tad too big at the moment. Leaving the 5.5l (AL40) and the 7L cylinder


Assuming your SAC will only double is a little unrealistic.
I would rather have more gas than nearly enough, hence the YBOD when 2x12`s were no longer big enough.
Not quite sure what your recommending here but it would seem like you think I should rework my calcs based upon a much higher SAC then draw up a cylinder from that?
 

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Hem, Hem, bringing this thread slightly more on topic
Your looking for an independent airsource for 40m no-stop diving?

I'd say that 40m is not really no-stop diving...

So your gas calc's really need to include some stops... Or your configuration needs to change...


:)
 

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Discussion Starter #16
Your looking for an independent airsource for 40m no-stop diving?

I'd say that 40m is not really no-stop diving...

So your gas calc's really need to include some stops... Or your configuration needs to change...
The OP should have been read I am looking for an independent airsource for dives that would be suitable for non-decompression dives UPTO 40m.

The majority of the dives that will be done with it won't get near 40m, but since 40m is plausible in no decompression dive plan with very little bottom time it is best that if I were to find myself at 40m on a dive like mentioned that I could get to the surface, but granted if I was regulary doing long dives to 40m, none of mysetup would be apporipiate cause that would most definately be decompression diving.
 

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A Moderate from 04/01/07-24/12/12
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The maths looks reasonable....only you know whether the input figures are right.

A couple of thoughts.....
If you are going to hang this on your right side it looks like it will foul your current AAS and a buddy will be confused as to which reg he is getting. Are you going to leave the spare gas turned on or off? It will disappoint your buddy if he goes from one OOG to another OOG in a few seconds.

How long are you expecting to be able to spend at 40m before you are into your 3 mins of reserve time and still avoid deco?
Mal
 

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I think you'll find the 7l is about 50% the price of an ali40 if that sways your decision any.
True the 7l is cheaper than the ali40 but you'll only buy it once and dive it lots of times. The ali40 will be much nicer in the water and you'll almost forget you are carrying it.
 

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Discussion Starter #20
A couple of thoughts.....
If you are going to hang this on your right side it looks like it will foul your current AAS and a buddy will be confused as to which reg he is getting.
Sorry if that was slightly confusing but I only had a pic of my right hand side but as stated below the photo I intend to have it on my left side which has the same d-ring config as left.

Are you going to leave the spare gas turned on or off? It will disappoint your buddy if he goes from one OOG to another OOG in a few seconds.
Reg will be tucked into a inner tube or similiar on the cylinder. Reg will be on providing it doesn't free flow a lot. If it does then I'd be tempted to turn it off but presurised it before entering the water, but at the moment I would intend for it to be on.

How long are you expecting to be able to spend at 40m before you are into your 3 mins of reserve time and still avoid deco?
Well on a square profile Bulhmann at 42m would be 9minutes, so at 40m if we run with those figures 6minutes would leave time to switch to AAS, get comfortable with it then ascend.
Again I wouldn't plan to do it cause 6m is quite a pointless dive in my eyes, but theoretically 6minutes max bottom time.
 
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