18L Steel Tank - advice needed

[David Novo]

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.

 

[runsongas]

the 18liter is a tall tank, so it kind of needs someone over 1.9m tall to dive it. why not consider doubles or sidemount instead for the extra redundancy?

 

[David Novo]

I am 1.88m (not sure if the 2cm difference is relevant ). I have no doubles or sidemount training and I am not planning to get it until then.

I am basically considering between a 15l or 18l steel tanks but would prefer the latter if feasible.

 

[runsongas]

it would be feasible, but unnecessary unless if you have a really high RMV.

 

[David Novo]

I have a really high SAC.
Please do not focus on the need for gas but on the safety, trim and balance implications.

 

[inka]

why not a 15 liters and a pony ?

 

[Tribal]

You don’t need training for doubles, you do need training for valve drills and valve failures. See it like this, you don’t have redundancy without training. You don’t have that with a 18l ether so if you really need that much air you better take a double 12l or 80cuft.

Are you sure you need 18l to keep up with most others on 11l? 15l handles well and is common to make up for example in the man/woman difference. 18l are very rare as solo tank.

 

[Storker]

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.

 

[runsongas]

trim and balance aren't too much worse than a 15liter. it is a LOT heavier than a 15liter though so you have to be careful walking around the deck and getting back on the boat with it as you would with doubles.

 

[David Novo]

Ok. Let's assume I do not have a doubles wing (nor planning to buy one this year) and can only choose between a 15l or 18l steel tank bottle (or 12l aluminium).
Let's also assume I need the gas.