Question Sidemount or backmount doubles?

[Wibble]

If you're staying within NDL I don't know why you'd want to go past singles. The complexity and expense goes up exponentially once you start getting into doubles of any kind. Just invest in a tank that can hold more gas. Most people should easily blow past NDL with an HP100 steel tank.

It's perfectly reasonable to use a twinset for recreational diving, especially off a boat. You've loads of spare gas available and can easily do two recreational dives on the same twinset without topping off.

The point of a twinset is it gives you that redundancy -- should you need it. If you're in less than ideal conditions (poor visibility, around wrecks, fishing nets, inexperienced divers) and are diving below 30m/100ft you should be carrying that for risk mitigation.

You're still diving within NDLs, thus "recreational diving" but carrying plenty of options that can be of great benefit should the crap hit the propeller.

 

[GF99/99]

I know there not common in the US but a 300B 7L twinset is the Cadillac of twins. Would be a dream to dive for recreational twinset diving.

Close to the same volume as LP85's but about 10kg less in weight.

 

[Wibble]

I know there not common in the US but a 300B 7L twinset is the Cadillac of twins. Would be a dream to dive for recreational twinset diving.

Close to the same volume as LP85's but about 10kg less in weight.
View attachment 708345

If you can get a fill to 300 bar. And if you're not doing a second dive. Most dive shops and boats can’t/won’t do 300 bar fills as they take a long time especially if you’re after a full fill (need to wait for them to cool before topping off whereas lower pressure cylinders can be overfilled hot to cool to the target pressure).

BTW those in the picture are narrow, so fiddling with the valves will be harder. You can get a wider band set which then puts the valves at the same width as a 12 litre twinset, albeit closer to your back.

Better still, just split them and use them for sidemount. Rather than 300 bar 7 litre tins, you'd be far better off with the 232 bar 8.5 litre tins. Supremely comfortable under the water.

 

[tbone1004]

@marsh9077 it's not that they're not common, they are not available. I'm not aware of a tank like that that has ever been made in the US. The closest thing we have are LP50's which are 7.8L but 300bar is well above their hydro pressure.

 

[Marie13]

I know there not common in the US but a 300B 7L twinset is the Cadillac of twins. Would be a dream to dive for recreational twinset diving.

Close to the same volume as LP85's but about 10kg less in weight.
View attachment 708345

LP50s are what are used for light doubles for recreational stuff.

 

[GF99/99]

@marsh9077 it's not that they're not common, they are not available. I'm not aware of a tank like that that has ever been made in the US. The closest thing we have are LP50's which are 7.8L but 300bar is well above their hydro pressure.

Yeah I have only seen them in EU, Oz and Asia. They are made by Faber but now that I think about it I don't think I have ever seen a DOT stamp on them so unless your filling your self would be pretty hard to get them filled or tested in the US. Its kind of like the 1.5L Luxfer ali fat cylinders. There perfect Sidewinder O2 tanks or wing/suit inflate tanks but no DOT stamp.

 

[boriss]

Ugh, I know I'm going to regret responding and getting pulled into the abyss... but here it goes. Keeping the OP's interests in mind.

It's perfectly reasonable to use a twinset for recreational diving, especially off a boat. You've loads of spare gas available and can easily do two recreational dives on the same twinset without topping off.

Yup, I do this, but I don't recommend it for non-technical divers. I do it for consistency and practice with my gear. It's the same reason Marines will go for a swim with their rifle and we don't. We could..... of course. There's the safety factor... anything wants to attack you? Shoot it! Ok, I'm joking, obviously.

There are some pros if you already own and use the equipment, but IMO it's not worth the investment for 99.9% of recreational divers.

The point of a twinset is it gives you that redundancy -- should you need it. If you're in less than ideal conditions (poor visibility, around wrecks, fishing nets, inexperienced divers) and are diving below 30m/100ft you should be carrying that for risk mitigation.

I would recommend a pony bottle instead and sticking with a good dive buddy. Having doubles requires additional expense, additional training, additional knowledge. It starts to make a much bigger impact on gear selection. For example, because of the additional weight you'd want to consider a double bladder wing, I had to upgrade my fins to give me enough propulsion, because the fins I used for singles weren't stiff enough and increased work.

I know your next argument to me will be small doubles, but again, I'm not talking about the 0.1% outliers. Additionally those smaller doubles may not hold enough gas for two dives with reserve.

You're still diving within NDLs, thus "recreational diving" but carrying plenty of options that can be of great benefit should the crap hit the propeller.

I just did two NDL dives to Lady Luck Wreck this past weekend. Used my doubles, while my dive buddy used HP100 singles. It's more work doing it with doubles and if you want to talk about safety, less stuff to go wrong is also safer. Less task loading is safer.

Again, I'll reiterate that a lot of arguments in this thread and many others are highly theoretical. Just because you can doesn't mean you should. I tend to see outliers presented as de-facto standards for all people.

The OP needs to figure out the type of diving he wants to do before investing in more equipment (AND TRAINING!).

 

[Pearlman]

Is sidemount a good choice for someone who is a UW videographer? I mean switching regs every 30 bar when he should really be holding the camera still so as not to lose capturing the moment… ?

 

[Wibble]

Is sidemount a good choice for someone who is a UW videographer? I mean switching regs every 30 bar when he should really be holding the camera still so as not to lose capturing the moment… ?

Really isn't an issue changing regs. Easily done one handed.

The additional stability and redundancy may make life easier.

 

[ginti]

Hi @boriss , I partially agree with your arguments, but I think it makes sense to add a little bit if you don't mind

However, before I start, I have a question and a friendly remark:
- have a question: Is your profile's dives' count updated?
- keep in mind that the OP clearly stated that he is interested in going beyond his current training level in terms of decompression

Yup, I do this, but I don't recommend it for non-technical divers.

I disagree. Small twin tanks for rec dives have some interesting advantages (I know you are not speaking about small twin tanks, but as a matter of fact they exist, and they are doubles), and doubles, in general, don't need extensive training. Training, yes, extensive training, nope. No reason to start tech training just to use doubles (tech training is intense, time-demanding and expensive; doubles training? nah).

There are some pros if you already own and use the equipment, but IMO it's not worth the investment for 99.9% of recreational divers.

Agree if we are speaking about big doubles; again, small doubles may be advantageous, but small doubles don't provide more volume of gas - they're exactly equal to a big single (or even slightly less). But, again, the OP seems interested in doing deco dives, so beyond the limits of what people commonly call recreational diving.

Also, there is the 0.1% of recreational divers who may find doubles beneficial. For instance, if you like to spend hours at very shallow depths.

I would recommend a pony bottle instead and sticking with a good dive buddy.

Pandora box opened!

Personally, I do not like pony bottles and I wouldn't recommend them. Anyway, I am not aware of any person who died because he was using a pony bottle, nor any person who died because was using doubles instead of a pony. At the end of the day, as long as we are speaking about recreational diving, it's a matter of personal preference, and if a person prefers doubles instead of a pony where is the problem? (or the other way around, obviously)

Having doubles requires additional expense, additional training, additional knowledge.

True, but if we are speaking only about doubles, these additional things are fairly small.

It starts to make a much bigger impact on gear selection. For example, because of the additional weight you'd want to consider a double bladder wing, I had to upgrade my fins to give me enough propulsion, because the fins I used for singles weren't stiff enough and increased work.

I didn't have to change fins when switching from singles to doubles, and I do not have a double bladder wing. It really depends on so many factors actually...

The OP is in the Netherlands, so I assume he is already using drysuits, giving him redundancy. With a drysuit, he probably already has lots of weights, meaning that his fins are likely adapted to provide a good amount of propulsion.

I know your next argument to me will be small doubles, but again, I'm not talking about the 0.1% outliers. Additionally those smaller doubles may not hold enough gas for two dives with reserve.

Small doubles are as big as a big single, so you're totally right here.

The OP needs to figure out the type of diving he wants to do before investing in more equipment (AND TRAINING!).

I couldn't agree more