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Discussion Starter · #1 ·
I've seen a few postings discussing the amount of weight to add/remove when switching from a single 12L or 15L to twins, but this question is actually going the other way!

As a result of my recent Advanced Buoyancy Control course, I know I need a total of 3KG of weight in fresh water using manifolded twin 12's. I also understand that I need to add the prescribed 2.7% when moving to salt water, which for me will be 3KG.

However, the club I have just joined do a lot of mid-week evening dives on the shallow reefs off the local coast, and I think using twin 12's for an 8m bimble would be a tad OTT!

I therefore propose to dust off the old 15L and dive with a single cylinder, but the question is what weight changes should I make, at least to get me in the ball park until I do a proper weight check?

The problem is, that looking back in my log book is nigh on useless as the last time I used the 15L my kit was completely different, since then I've bought the dry suit and undersuit and also changed just about every aspect of my kit.

I've looked up the cylinder buoyancy calculations here UK Scuba - Cylinder Buoyancy Calculation but all that physics just confuses me! :confused:

The closest I can get is that the twin 12's seem to have 2.5KG of buoyancy when empty and the single 15L has 1.5KG when empty, but does that mean I add (or subtract?) 1KG or what?

Help please!:redface:
 

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Gav,

This might not be much help, but here goes. I think a lot depends on how different your kit will be on the single compared with the twins. Yes, the 15 will be less positive when empty than the twin 12s, but you have to take into account that you won't have a second first stage, you won't have a manifold and the single wing may have an impact (but I'd think this would only be marginal compared to the difference in regs and tanks). Like you I haven't actually done a proper weight check when I dive the single 15, as I don't dive it much, but I do use more weight than when i have the twin 12s, probably about 2 or 3 kilos more.

Dave
 

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You need to add weight when going onto a single. I add approx 7kg (3 normal blocks and 1 half block), thats for a 12litre tank.
 

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Any number we come up with is going to be wrong, you can look at all the diffrent points and play a round all you like but the best think is to go there do a wight cheak then you will know

sorry if that dose not sound help full but to be honest you will find it to be true
 

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Discussion Starter · #6 ·
The only thing I'll be changing is the wing (from double to single) and the cylinder, so I'll try adding 2KG to the belt and with a 2KG backplate and other ditchable weight that'll leave me 1KG lighter than when in a wetsuit and try a buoyancy check from there.

Thanks for the comments. :teeth:
 

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like I say you can do all the maths you like but you will still have to fine tune it to get it right. of that I can promise you
 
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