Twin strategy for a days diving

[Turtle Dude]

This might be a mad, and over complicated (please say if you think so), but would this strategy with twins work?

Am working out what cylinders to buy for my UK diving (gave my old ones away a while back and now am back).

Diving will be typical UK club diving 20-50m, importantly 2 dives in the day (usual first deeper than second shallower drift). Air is fine.

I do not want the weight of twin-12s 232bar or twin-10s 300bar and managing my air across 2 dives; plus I don’t want that much weight on my back at any one time. Neither do I want to have to go and get a twin filled up in between dives in the car to the nearest air station. Am after the convenience of just switching a bottle which is already filled.

My default, as I have done before, is two singles (probably this time 300bar 12s) and a 3L pony; however, I had an idea – how about a twin-7 300 bar set up, where after the first dive I switch one of the 7s with a fresh one (already filled). Therefore needing only 3 bottles for 2 dives.

It means:

I have to have three cylinders with me for the day (am OK with that)
I have to manage the balance of the air from the first dive not evenly (but could do this and still keep a good safety margin). I.e. on the first dive leave one with 50 bar and the other with 100bar – and add the fresh one to the 100bar one.
I have to be able to easily switch one of the cylinders on the Zeagle BCD – this I have not tried, as I have not run it with twins, and need to check a suitable way of switching just one bottle.
I accept the risk that I can get fills at 280bar+ (but should be OK having them filled the week before I go)


Mad idea or feasible?

[Robin]

I pretty much use this strategy, although with 232 bar independent twin 10ltrs.

Use three of these, swap regs regulalry but end up with more gas in one at the end of the first dive.

Then swap a full cylinder with the nearly empty one gives you plenty for the second dive.

Having said that on a fairly shallow shake down dive this weekend I returned from the first dive with 200/30 and was 'coached' by the Dive Manager for not having 50 bar left. My response was that I had checked the second cylinder/reg was working OK and had used 20 bar from it, thus I knew my bail out was functioning correctly

The other advantage of this set up, assuming you are drysuit diving, is that you can have two totally independent sources of bouyancy but ruuning one inflator off each reg.

Have beewn diving this way for 5 years, it works for me and I think is a great set up.

I havn't used 300 bar 7's but suspect they give no advantage over 232 bar 10's - which yopu can always get a good fill in.

[Turtle Dude]

I pretty much use this strategy, although with 232 bar independent twin 10ltrs.

{snip}

Have beewn diving this way for 5 years, it works for me and I think is a great set up.

I havn't used 300 bar 7's but suspect they give no advantage over 232 bar 10's - which yopu can always get a good fill in.
What set up do you have for the BCD? is there a quick release system for single tanks from a twin?

[Nigel Hewitt]

What set up do you have for the BCD? is there a quick release system for single tanks from a twin?All the quick releases I've seen tended to move the tanks at least another inch and a bit further back and your stability in the water goes down quite noticably.

The one thing I liked about twins was the way the set was far snugger up to me and actually made me more stable that a single sticking way out from my back wanting to roll me over all the time.

[Robin]

What set up do you have for the BCD? is there a quick release system for single tanks from a twin?

I use Buddy twining bands so no quick release - takes about ten minutes to change to single bands.

Nigel's comment is dead right - it's so much more balanced and comfortable diving twins v single & pony

[Nick Argue]

An alternative strategy is to use manifolded 10's and decant into them after the first dive. I use a 232 bar 15 to top off my 10's which generally gives enough air for a decent second dive.

[Chris aka divingchef]

An alternative strategy is to use manifolded 10's and decant into them after the first dive. I use a 232 bar 15 to top off my 10's which generally gives enough air for a decent second dive.

Yepp
I've seen this a few times but with twin sevens, works a treat !

[Turtle Dude]

I guess the advantage of decanting is that you can have a fixed twin set with a combined manifold (with an isolator valve).

[NJT]

I have dived with a guy who has 4 7's. 3 to do the system you are looking at plus one as a side slung with 36% for deco / ascent. I think he was using Buddy twinning bands as well.

Regards
Nick

[Turtle Dude]

For a shallower second dive, with a twinset, would people prefer to decant (from a larger single) or swap in a third tank? I can see the pros and cons either way.

I just don't fancy shifting two twinset in the car.

ps: I supose the third option is a single tank for the 2nd dive, with a H-valve so the regs can be easily reused in their left/right set up.

[Dave Whitlow]

Someone in our club dives on manifolded twin 7's and changes sets after the first dive. It doesn't take long to undo two mushroom nuts and swap to the second set but gives him the redundancy of 12+pony with less regulators, better balance, and less weight.

[Gav]

Not the cheapest option, but one that evolved when moving from single 15 to twin 12's.

I now have two complete set-ups; twins for deeper than 20m, single for shallower. No swapping or changing over as each set has their own regs etc. If diving off rib we return to marina between dives; if off hardboat then I can take both sets.