Twinset Weighting?

[StevenSeagull]

Hey guys.

Just upgraded to a shiney new twinset courtesy of those lovely chaps at the dive show and need some advice on weighting.

I'm 6"1' and around the 13st mark. have previously dived single steel 15lt + 3lt pony and used 10kg on my weightbelt with my current drysuit/undersuit combo in scapa.

should have been fairly accurate although never did a 'proper' weightcheck after adding the pony, just took 2kg off belt.

Now diving a steel twin 12lt setup with a 3mm frog backplate. i know i'll need a weightcheck but could do with a couple of ballpark figures to aquire weight blocks etc. also what difference do you guys find you need to alter for fresh water from salt (should the need ever take me) or is it largly negligable?

thanking you verily

[Frankie Price]

I use 8Kg in salt and 6Kg in fresh with my Faber twin 12's with 3mm SS back plate and find that is more than enough to keep me negative with 50bar back gas and 20bar 7 lit ali stage.
I am 6' 2" and 17 stone.
Hope that helps.

[nickb]

I'm a similar build and used around 10kg when I dived a 15l/pony.
I now use 4kg in the sea and 2kg in fresh water with twin Fabers and a 3mm Halcyon backplate.

I do run my drysuit quite tight with the auto-dump all the way open bar a couple of clicks.

[StevenSeagull]

Ah, i had a stab in the dark and rekoned around 4kg. i think i may have been a tad overweighted on 10kg 15lt + pony so 4kg should be sufficent. didn't realise fresh water would have made a whole 2kg difference though.

Cheers for the responses

[ianfirmin]

I went from a single 15 (without pony) to twins of varying size. I checked the weight and buoyancy of all of them (without regs). Results for Faber single 15 vs. twin Faber 12's as below:

Twin 12's (with rubber boot) at 232 bar weighs 37.9 kg (6.6kg air), steel weight 31.3 kg.
Buoyancy full = -8.9, 40 bar -3.5, empty -2.3

15l single at 230 bar, full weight is 22.1kg (4.1kg of air), steel weight = 18.0kg.
Buoyancy full = -4.2, 40 bar -0.8, empty -0.1

Thus, the twin 12's were about 2kg less buoyant. Add another kilogram for the extra primary regulator and stuff and you have 3kg less weight to carry.

Weighting also depends on the difference between your harness/bcd (wing and plate?) using the single and what you are using now. E.g. a steel backplate has less buoyancy than an aluminium one.

Rule of thumb take 2kg off your belt for the twins. Add 2kg for salt water from fresh water. Do a test.

IMHO unless you can stay at 2m with 10 bar or less then the extra gas in the twins is just there for ballast and not available to breathe. Better too heavy than too light....

ATB
Ian

[steve2056]

Originally Posted by StevenSeagull

also what difference do you guys find you need to alter for fresh water from salt (should the need ever take me) or is it largly negligable?

thanking you verily

Try my Buoyancy calculator here: Utilities & Dive Information

Plug in values for your setup for salt water, calculate and note values. Now select Fresh water and note the difference. I get around half a kilo difference for a steel 12 litre cylinder.

[steve6690]

I changed from a single Faber 15 to twin Euro 12's last week. Everything else remained the same. I did a weight check and removed 4.5 kilos. I add about 2.5 kilos for sea diving

[RobbieS]

Originally Posted by StevenSeagull

Didn't realise fresh water would have made a whole 2kg difference though.

Not twinset related but my weighting went from 6kg in the fresh stuff to 11k in the salty stuff using the same set up. Go figure eh?

[Fiona]

Originally Posted by StevenSeagull

didn't realise fresh water would have made a whole 2kg difference though.

Someone needs to go back and read their novice diver lecture

[neilh]

Originally Posted by RobbieS

Not twinset related but my weighting went from 6kg in the fresh stuff to 11k in the salty stuff using the same set up. Go figure eh?

I have about a 5Kg difference too. Any less in the salty stuff and it doesn't feel "right" and in control.