Twin 7's with BC (jacket style) possible?

[lynsey.a]

Hi,

Im looking for some advice please.

I am currently seriously considering purchasing twin 7's (300 bar).


For a few reasons - i will be able to do deeper and longer dives, i feel that it will be more comfortable on my back, less hoses around me (pony regs and pressure gage) and will be safer as i would have a greater air supply in an emergency.

I will be able to do 2 dives off it no problem - my current two tanks are 8ltr 300bar, and 9ltr 203bar with a 1litre pony.

My problems are these -
i dive with a northern diver BC - i have checked and the label in the pocket states that it can have twin 12's on it maximum.
But how would i attach it? The plastic backplate only has slots for a single cam band (rules out the buddy twin bands) and i cant see how SS bands would bolt on to it. The two bolta that are on it bolt the current standard plastick backplate on the inside to a light small one on the outside of the BC.

Would i buy an aluminium (lighter for taking on holiday) backplate and bolt it on instead of the plastic one that is standard? (keeping the plastic plate on the inside of the bc with the aluminium on the outside of the BC instead of the standard plastic one?)

The reasons that i wish to keep my curent BC (instead of purchacing wings) is that i am comfortable in it, i know it well, it fits well, has plenty of lift and i dont wish the expense of buying a new one!

So what do you think? I have carried out google and forum searches about this but i was unable to come up with anything.

Cheers!
Lynsey.

[Fiona]

Lyndsey

When I first got my twin 7's 232's I used them on a Mares Vector jacket. I had it fitted with an SDS latching system. However while I was instructing one day I didn't feel the BC gave me enough support at the surface so I changed to a wing.

I don't know how much lift the ND jacket has so I can't say if it will be suitable.

[divingniknaks]

Hi,

Hmmmm 300 bar 7's , if the reason is thinking you'll get 300 bar fills, then stop now, because you won't I'm afraid. I think the current average is 260-270 bar, so you end up with not much more gas , and quite a bit more weight in 300 bar 7's.

That's one out of the way, if you want to twin any size , I think you might have a problem as your existing rig is not really designed for twins, unless someone can step up and point out I'm wrong (feel free I don;t mind )

That probably wasn't what you wanted to here I know, if you want to talk through options , feel free give me a buzz or Skype me. Talking costs nothing or little

Cheers

[Paul Oliver]

Why don't you talk to ND about the latching system to use? They may well have the answer

I dive an ND Guardian with a steel 15l and steel 3L Pony and there is plenty of lift, its also very comfortable.

I have seen lots of people diving twins on a BC, and i dive on an AP valves BC with my twin 12L, there are no problems and it all works well, but my BC is a military pattern one designed for twins.

I also think Phil's comment about the fill Bar is spot on, mine are 232 and i do the filling but i still often get less than what they can take

[lynsey.a]

Actually - just checked and it is a Northern Diver Guardian BC too! (http://www.diveshop.co.uk/pages/special_offers.html or http://www.divernet.com/gear/dtst499.htm#guardian for details)

Do you see any way that twins could be attached?

The diagram on the BC has led me to believe that there is a way of mounting twins on it as it pictures them!

Im not really concerned with the fills - with my 8ltr cylinder just now i get around 290bar in it at my local shop (Glasgow). I usually drop them off and collect them a few days later forcing them to top it up! (once they did give me 200bar and i was not a happy bunny!).
I still feel that even if the fills are not perfect i will have more air for 2 dives than my current set up (my 9ltr cylinder is only 203bar!)

Im a wee person with wee lungs after all! (but looking for the opportunity to stay down on deeper (35m+) sites for a bit longer, the second dive of the day i usually have plenty of air left since its an easier and shallower dive generally. Thought the twin 7's might balance the discrepancy in air usage out)


Looking again i think that my only viable option is the buddy twinset bands (http://ccgi.apvalves.plus.com/access....php?codeID=10 ) but i would be worried that it would actually be quite difficult to get it fitted to the correct size (ie. tightly!) with the blocks and 'rubber strips' to match it to the manifold size! It may end up a little unstable i feel.

Think ill give ND an email to see what they suggest since they say its suitable!

Thanks,
Lynsey.

[String]

Originally Posted by Fiona

However while I was instructing one day I didn't feel the BC gave me enough support at the surface so I changed to a wing.

Ive got a Mares Vector jacket (Chrome) and whilst testing something totally different in the pool i had a full 15l and full pony on it. With the jacket fully inflated to the point of air coming out of the overpressure valve if breathed out i could actually start to descend. Leads me to believe theres a similar issue to yours - life would appear to be substantially less than quoted.
Id never noticed before as ive always had pony/15 combination in salt water with drysuit.

[Fiona]

Originally Posted by lynsey.a

Im a wee person with wee lungs after all!
Thanks,
Lynsey.

Blimey then Lynsey have you tried to pick up 300bar twin 7's

If I remember correctly I think SDS drilled the plastic backpack on my Mares, so that might be a solution.

[Mark Chase]

What Fiona said

I had a Seaman Sub jacket type BCD and I drilled the plastic back plate to take the studding for the SS banded twin 12s I was using. It was OK but you have to get the position of the tanks right before turning your back plate in to Swiss cheese. My BCD didnt have enough surface lift to suport twin 12s 232 bar so I quickley mooved on to a wing.

ATB

Mark Chase

[Rob Dobson]

I'd look seriously look at 232 twin 7's or 232 twin 10's if you need that much air.

232 10's probably weight about the same as 300 bar 7's but you can get proper fills and don't run into issues with the gas laws (even with a full fill you can't 300 bars worth of air into a 300 bar cylinder, the gas laws go a screwy over 232 bar).

Good luck.

[chrisch]

Originally Posted by divingniknaks

....Hmmmm 300 bar 7's , if the reason is thinking you'll get 300 bar fills, then stop now, because you won't I'm afraid. I think the current average is 260-270 bar, so you end up with not much more gas , and quite a bit more weight in 300 bar 7's.

That's one out of the way, if you want to twin any size , I think you might have a problem as your existing rig is not really designed for twins, unless someone can step up and point out I'm wrong (feel free I don;t mind )

....

Echo.

I would get a new wing and twin 232 7.5L That in my mind is a nice rig. I wish I had bought something like that ages ago. I've struggled with the twin 10s and all the new kit - old habits die hard etc. A stab type jacket is the least suitable BD for twins.

Chris

PS I meant to add - please I hope you take the comments as positive from all of us! I think you have thought through the situation and come up with the right way to go. Ponies are pants. Have some brownie points or a green thing or whatever!!