18L Steel Tank - advice needed

[runsongas]

take a yoga class, work on propulsion and buoyancy, and use the 15liter is my recommendation

 

[Degenerate]

No. No, no, no. A twin 8.5 rides infinitely better on the back and isn't half as unwieldy. And holds 95% the amount of gas.

You really, really don't want an 18.

I'm guessing there aren't a lot of liveaboards that have twin 8.5 232 bar sets on board, but I could be wrong.

 

[David Novo]

take a yoga class, work on propulsion and buoyancy, and use the 15liter is my recommendation

Let's leave the high SAC rate discussion for a different thread.

trim and balance aren't too much worse than a 15liter.

Thanks.

 

[Doppler]

David: You're asking for opinions, and here's mine. A steel 18L is a huge mother of a thing to manage... speaking for me, an experienced diver. It's difficult to trim (I'm 180 cm).

More important perhaps, are you calculations for weighting. Are you considering the mass of the gas and the buoyancy shift start of dive vs end of dive? Not sure what pressure your liveaboard is charging its tanks too, but let's say 220 bar... that's a starting mass of almost 4 kgs. This might make a difference to your need for ballast.

 

[David Novo]

David: You're asking for opinions, and here's mine. A steel 18L is a huge mother of a thing to manage... speaking for me, an experienced diver. It's difficult to trim (I'm 180 cm).

More important perhaps, are you calculations for weighting. Are you considering the mass of the gas and the buoyancy shift start of dive vs end of dive? Not sure what pressure your liveaboard is charging its tanks too, but let's say 220 bar... that's a starting mass of almost 4 kgs. This might make a difference to your need for ballast.

Yes, I am using the optimal buoyancy calculator spreadsheet that is on a sticky thread somewhere here. I have it calibrated for the configurations I usually use and was testing for the 18L tank.

Regarding trim, that is one of of my worries, hence the post. I will take that into consideration. Thanks

 

[Compressor]

Hi,

I am considering renting a 18L Steel Tank for a liveaboard and would like to know the general consensus on this. I am going with a 13L wing, a steel backplate and a 7/8 mm semi-drysuit.

According to my math, I will still require 4kg of ballast on a weight belt, with a wing failure and dropping the belt, I should be c. 5kg negative at 30m, with seems a realistic weight to swim up (while freediving I already swam up on a 5mm wetsuit, 10kg of ballast from 10m, which is slightly more negative than that).

Do these calculations make sense?
On a different note, how is the impact of a 18L steel tank vs 15L steel tank on trim and balance?

Thank you.

Go ahead and rent it. If your trim works out then fine, use it for the rest of the trip. If not then ask to switch cylinders as recommended but the audience above.

 

[Storker]

OP, are you looking for advice or for confirmation? If the former, you've come to the right place, there are a lot of experienced divers here. If the latter, not so much.

 

[David Novo]

Go ahead and rent it. If your trim works out then fine, use it for the rest of the trip. If not then ask to switch cylinders as recommended but the audience above.

There were two people that recommended a 15L tank and none of the two said why it would be better than a 18L tank (assuming I need the gas).

OP, are you looking for advice or for confirmation? If the former, you've come to the right place, there are a lot of experienced divers here. If the latter, not so much.

Advice given the restrictions I have, specifically information on how does a 18L single tank affect my trim and balance and whether it is safe. Do not take me wrong, I appreciate the advice. Some of them ("doubles") is just not realistic given my constraints.

I am trying also to understand the reasons underlying each advice so info as "it is hard to trim" (as was already pointed out) is useful. Plain "use something else" without an explanation, not so much.

 

[Storker]

Plain "use something else" without an explanation, not so much.

Well, I'm pretty certain there's a reason I see twin 8.5 sets almost every diving day, but i still have to see a single 18. I don't have the explanation, but I'm convinced there is one. Probably a good one. And I wouldn't be surprised if it had something to do with how a big-arse 18 balances vs how a twin 8.5 balances, or perhaps the weight of them.

Don't be allergic to twins. Some people on SB seem to love to harp on about how twins are fundamentally different from singles and how you need to know this, master that etcetera to dive twins. Well, a rec twinset is no different from a single. It's just shaped differently. You can even eliminate the isolation manifold and go for a simple steel tube manifold and dive the twinset just as you'd dive a single.

 

[David Novo]

Well, I'm pretty certain there's a reason I see twin 8.5 sets almost every diving day, but i still have to see a single 18. I don't have the explanation, but I'm convinced there is one. Probably a good one. And I wouldn't be surprised if it had something to do with how a big-arse 18 balances vs how a twin 8.5 balances, or perhaps the weight of them.

I do not doubt you are right in a non-constrained scenario, I am just trying to go from faith to reason on my specific case.

Don't be allergic to twins. Some people on SB seem to love to harp on about how twins are fundamentally different from singles and how you need to know this, master that etcetera to dive twins. Well, a rec twinset is no different from a single. It's just shaped differently. You can even eliminate the isolation manifold and go for a simple steel tube manifold and dive the twinset just as you'd dive a single.

No allergy at all to any scuba equipment. It is just not exactly the same as I would have to own a doubles wing and tanks, which I don't...