Weight between double and singles on and off the boat

[Unbalanced]

Thank you all for your replies. I did the cylinder calculations using: UK Scuba cylinder calculator. Agree this wouldn't have included the valve weight - so with that and a bit of air it would be neutral.

That is very helpful. Given the amount of weight we need - with the exposure suits - most of the guys with twins use a trolley to get the twins from their cars to the boat.

Thanks again, I will read through this carefully and this is very useful advice. I think I will lean on the local scuba operator to let me try some doubles, at least on land and I can work out if I can handle it. If not I will go with the smaller pony bottle.

 

[randini]

In my old gig, I used the same backplate and harness between single tank (12l steel) and double configurations (2x 12l steel). For me, all else being the same (same drysuit, undies, fins etc) I use 8kg less lead in doubles than when I'm single tank. YMMV

 

[justinthedeeps]

You are completely right to ditch anything with a manifold if you are concerned about weight.

Approx fully rigged weights for drysuit diving in cold water (≤10ºC), all steel cylinders:

~50kg Twinset HP100's (2x 12.2 L) + ~5kg of plate & lead
~37kg single HP100 (12.L) + ~10kg of plate & lead

Weights lower for warm water, but similar savings.

It is easy to just dive single-tank, then carry a normal extra cylinder as a side-clipped stage, if/when needed. You don't even need to go all "sidemount" either (but you could). You get the same advantages of redundancy and spare gas for repetitive dives, with no need for manifolds or twinsets. Much easier plan for travel diving too. Just pack an extra regulator and stage rigging kit.

I've not heard of anyone actually needing the small specific advantages of a manifold (or 'valve drill') ever. It's just something that has stuck around from the early days of cavers bashing them into rocks, and people with poorly maintained regulators. With two independent tanks+reg and no manifold, you can still handle one reg failure.

 

[RyanT]

You can dive with a pair of 7 litre cylinders which would give you the gas redundancy and will only be a "bit more" heavy (second regulator, manifold) than a single 15 litre steel.

@Unbalanced, in case you missed it, I was also going to suggest this as an option. A twin set of 7L (roughly 50 cf tanks in imperial) will be only a little heavier than most single tank configurations. It will give you all the advantages of doubles and they're quite easy to dive, climb ladders, and move around. The only downside is that compared to larger doubles (12 or 13L tanks), you often won't be able to make two recreational dives with them. In which case, you dive once, or bring another 7L twin set.

 

[justinthedeeps]

Confirmed mini LP50 twinset is same total dive weight as a single HP100, and gives redundancy.

I took this to Gods Pocket once where they top up your cylinders between dives, right on the boat! Even while out and about!

Everywhere else though, has been quite simple to just dive single-tank, and add a stage cylinder if/as needed.

 

[halocline]

If you are a recreational diver doing NDL limit OW dives, with a buddy, I would question your need for redundancy. It’s very unlikely to increase your safety as much as simply diving with good partners and diving responsibly. But…..if you are determined to carry an extra bottle on single tank recreational dives, and you want to minimize extra weight, just carry a small bail out bottle, like a 19cft AL pony, and sling it. If you really need more than that to reach the surface safely and calmly, you are doing something wrong, like seriously pushing the limits of no decompression OW diving. I realize that’s not a popular opinion on a dive forum, but so it is.

Carrying an entire extra tank on the type of diving you do now with a single tank is overkill. There are lots of reasons to dive with two tanks (either twin sets or independent doubles) but having extra emergency gas on a recreational OW dive is not one of them. If you want to do the kinds of dives where it is appropriate to carry doubles, great! Just train for that type of diving and your instructor will help you choose the best gear configuration.

 

[Wibble]

Given the amount of weight we need - with the exposure suits - most of the guys with twins use a trolley to get the twins from their cars to the boat.

Wow, how far are the cars from the boat? More than a kilometre?

That’s about the distance we walk them, plus up and down a 60m/200ft hill…

Seriously, carrying them a few hundred metres/3.3x a few hundred feet from the car to the boat. You’ll need to do it in a couple or three trips: twinset/rebreather; deco/bailout cylinders; climbing rucksack with fins ‘n crap; drysuit and undersuit. It’s a sport and good for you

 

[jborg]

It’s a sport and good for you

Not great when you're bubbling after the dive though :/

 

[Unbalanced]

Thanks again for the replies - and agree the smaller twin cylinders if I was only after redundancy would be a good option. I live a fair way from the water and enjoy the double dive and I need a 12 litre cylinder to keep up with typical buddies. So I am stuck with 2 x 12 litre cylinders.

I am joining up with a club and I hope that I will get more reliable buddies. The random buddies down this way are not the most reliable. The training since when I first started seems to have given up on drilling it into buddies to stay reasonably close to each other - so with the wisdom of age (surely there has to be a benefit of getting older) - I'm getting back into a club and thinking about redundant air for those random buddy occasions and the deeper dives.

The double tank folk down here like the extra reserve air and they like the trim (for the back mount folk) - and to avoid the hassle of swapping tanks on the boat. I could use the extra reserve with the 12 litre tanks (and the redundancy). But twins are a real tradeoff. Then the small question of manifold/back mount or side mount - another interesting question.

I am now confused and in a nice to have dilemma. I think I will have to try some twins to know if I will enjoy them and/or try a pony bottle option. Sounds like it may be more about giving it a go to work it out in practice.

Thanks again
UB

 

[halocline]

Thanks again for the replies - and agree the smaller twin cylinders if I was only after redundancy would be a good option. I live a fair way from the water and enjoy the double dive and I need a 12 litre cylinder to keep up with typical buddies. So I am stuck with 2 x 12 litre cylinders.

I am joining up with a club and I hope that I will get more reliable buddies. The random buddies down this way are not the most reliable. The training since when I first started seems to have given up on drilling it into buddies to stay reasonably close to each other - so with the wisdom of age (surely there has to be a benefit of getting older) - I'm getting back into a club and thinking about redundant air for those random buddy occasions and the deeper dives.

The double tank folk down here like the extra reserve air and they like the trim (for the back mount folk) - and to avoid the hassle of swapping tanks on the boat. I could use the extra reserve with the 12 litre tanks (and the redundancy). But twins are a real tradeoff. Then the small question of manifold/back mount or side mount - another interesting question.

I am now confused and in a nice to have dilemma. I think I will have to try some twins to know if I will enjoy them and/or try a pony bottle option. Sounds like it may be more about giving it a go to work it out in practice.

Thanks again
UB

Swapping the hassle of taking 2 minutes to switch tanks during a surface interval for all the extra work of carrying 80 lb doubles or fiddling with SM tanks on a boat is not a good swap. You’re making things much more difficult for yourself. Just use a single tank like the other 99% of millions of recreational divers around the world.

Sorry, I get a little impatient with this topic, it comes up frequently.