Red Sea Liveaboard 15litre Advice

[Neill]

Some advice would be welcome. I have organised a RS trip. People have asked me about hiring 15litre cylinders. I gave them the following advice but am now full of doubt. Am I wrong, right or maybe-ish.

"15 litres cylinders are £25 pw and Nitrox is £60 for 12s and £80 for 15s. I was thinking 12 + Nitrox then fancied a 15. This is £45 more and just not worth it.

Recently Rob and I have been diving to 22m for 39mins in 10c water (drysuit encumbered) Rob has a 15l and comes up with 90 bar and I (12litres) come up with 60 bar. The deco penalty on that kind of diving four times a day will be at the limits. An aluminium 15l is heavier dry but more bouyant ( I know there are some engineers who'll eat me alive if I get this wrong) at 50 bar. You end up carrying more lead to stay neutral at 6m/ 50 bar. This weight/trim will mess with your air consumption negating the value of the 15l. So 45 quid for minimal benefit - just say no.

Believe me 15 litres will mess with your mojo. For air consumption management I will be doing brief CBT for divers sessions."

please be gentle.....

[tom]

Well, the 15s will probably be steel not ali. You probably won't be doing many square profiles so the deco considerations may vary. Also, your gas fills will most likely be less than you are used to here (maybe 200bar).

Personally, I'd have a 15 of nitrox, to maximise dive time - £45 is pretty insignificant in the grand scheme of things.

EDIT: and remember of course that other people may have wildly different SACs to you and your buddy.

[grazie42]

The 15l will propably be steel.

My regular buddy uses a 15l at the same rate that I use a 12l, if he were to go with a 12l it would cut our normal dives short. If he told me it was because the organizer "told him" to do that, I´d be a pretty unhappy camper...

[Conor]

If you are in doubt about your sac get a 15. I had a 15L hired on a Red Sea liveaboard and never used it, I found I could go into minimal deco on a 12, even using an appropriate EANx. But I am glad I had the option.

I don't think the difference in size etc actually contributes to a noticible increase in air consumption. And as already said, just because the 12s are ali doesn't mean the 15s will be......I have seen both. The lead argument only really makes a difference out of the water and on a liveaboard that time is negligible.

I would say if anyone is worried about air consumption hire a 15, they will probably be more realxed because of it and will end up back on a 12 with a better SAC by the end of the week. That said with 4 dives a day, there is no real need to overstay down there

ENjoy the trip ya lucky ....

[David D]

As posted by others, 15ltr will probably be steel. So [though I don't have any facts and figures] this seems a better tank selection to me than an aluminium 12ltr. Since it's more negative than the ali 12ltr, it's less lead per litre of cylinder.

Personally, I'd rather pay the money, in the full knowledge that it's a complete rip off, and have the gas in case of strong currents, deeper sights, etc.

[jorawley]

I always hire a 15l on livaboards, purely because even after an hour down there, and at a 5m stop with 50 bar its sods law that something will be incredibly interesting to stay at 5m or shallower to try and photograph...

(from log book)
one dive at elphinstone, we were dropped off by rib and spent about 55 mins drifting back to the boat, hung on the shot under the boat in about 5 - 10 metres watching the oceanic white tips above (have to say my breathing rate did increase at that point) for at least 20 mins. On a 12 i would be rather too low on air, on a 15l still 30bar ish.

Entirely your choice of course - enjoy the trip. When and where are you goin?

[Sparky]

I've always hired a 15l on livaboards as I really do not like diving with ali's, they are steels, it also gives you a margin of error if as previously mentioned something interesting always appears just as you are getting out, I think I paid £25 for the weeks hire of that and £60 for a week of nitrox or if you think you'll only need nitrox for a couple of dives it was £5 a dive.

[endoman]

I'll be taking my pony to sharm just so I know I have that bit of extra. Shore based this first time, but maybe liveaboard later in the year

[DIVE BUDDHA]

Go for the 15 litre as it will give u that little cusion on bottom time !
i used 12 litere cylinders last year and they where ali not steel !!!

[MJH]

I dragged an OOA diver up off the Thistlegorm a couple of months ago. From a depth of 30m with a 3 min stop on the way up we got through just over 100bar from my 15L cylinder.

I work out min gas when dive planning – but to actually use that much gas was a huge reality check.

My sac is usually around 18 in the Red Sea.

It also made me fully realise the benefits of diving a long hose esp with a very stressed buddy attached

I will never again economise by not paying out for a 15L cylinder