Is this BCD's buoyancy enough for me?

[Roberto Inzerillo]

Hi there
I've been gifted a used Mares Vector origin BCD. It's ok, good conditions, normal wearing but not bad at all. I already used it once on a shallow dive and I am generally happy with it but I am not entirely shure about the buoyancy it can provide.

I am 1.85m tall, 80Kg, I dive with a 7mm semi-dry suit and 8Kg on my belt. How much buoyancy should a proper BCD provide in this case?

This BCD is size S, a bit small for me, I have small shoulders and I generally use a size M and this one is a bit on the small side for me, although it fits without being unconfortable. Still, I wonder if it is too small regarding the buoyancy it can provide.

I am quite new to scuba so I have not much experience with the numbers. I can't find any decent specification sheet for this model but inside the pouch there's a plastic sheet with "Maximum buoyancy: N 120" on it (see picture).
What does that mean? Is it enough for me? Does it make any difference when I dive deep (well, 30m or so, not deeper)?

 

[dmaziuk]

there's a plastic sheet with "Maximum buoyancy: N 120" on it (see picture).
What does that mean? Is it enough for me? Does it make any difference when I dive deep (well, 30m or so, not deeper)?

Convert newtons earth N into pounds lb - lbs weight and mass for culinary practise

Basically it needs to be enough to
- float you with all your gear and full tank on the surface, and
- compensate for loss of buoyancy to wetsuit compression at depth.
That last bit gets more important with thicker suits (they have more buoyancy to lose) and deeper dives (= more compression).

I've seen the numbers for wetsuit compression at depth but I can't remember where. Hopefully someone who does will chime in. Edit: and then I've no idea how/if to adjust the numbers for semi-dry -- probably no need to, but I don't know.

 

[hammet]

That's 12kg of lift. (newtons units of force ... F=mg where g is the acceleration on earths surface due to gravity.... 9.8m/s/s and m is the mass in kgs)
If you have 8kg of lead, that gives you 4 left.
Your regulator is at least 1kg and add another 1kg for other gear.
That's 2kg left for your tank.
You didn't say what kind of tank you use, but if you use an AL80 that will add 1kg when full.
That gives you 1kg of lift to spare.

 

[dmaziuk]

... That gives you 1kg of lift to spare.

Yes, but on the surface you also have the buoyancy of a 7mm L/XL suit, you just need to ditch lead if *it hits the fan.

 

[Roberto Inzerillo]

You didn't say what kind of tank you use, but if you use an AL80 that will add 1kg when full.

I generally use 15l steel.

 

[dmaziuk]

I generally use 15l steel.

That sounds a bit much. I've no problem diving in 7mm (I am 185/80-ish) w/ an 11kg aircell, but the lakes here are less than 10m deep. I would hesitate to go on a 30 m dive with my wing.

 

[Roberto Inzerillo]

Yes, but on the surface you also have the buoyancy of a 7mm L/XL suit, you just need to ditch lead if *it hits the fan.

I have to add I did a buoyancy check on the surface with full gear and full tank (15l steel at 220bar), empty BCD, I can easily float when inhaling, and drop down when exhaling.
And at the end of the dive I would easily stay for 3min at 5m with 50bar in the tank without balooning.
So I guess buoyancy provided by the BCD is enough on the surface and I'm not way too heavy without inflating it.

I am more worried about the deep dive, when the BCD has to compensate for loss of buoyancy of the suit.

 

[Roberto Inzerillo]

That sounds a bit much. I've no problem diving in 7mm (I am 185/80-ish) w/ an 11kg aircell, but the lakes here are less than 10m deep. I would hesitate to go on a 30 m dive with my wing.

That's exactly what I am referring to.
What maximum buoyancy value would you suggest for such a case? How much does a 7mm suit loose each 10m (1atm) deeper?

I read current Mares BCDs (let me refer to those ones for a basic example) size M range goes from 150N (16Kg) to 200N (21Kg). Will 3Kg more be enough? Should I go for the big numbers?

 

[Roberto Inzerillo]

Btw I dive at sea, no lakes here.

 

[hammet]

Yes, but on the surface you also have the buoyancy of a 7mm L/XL suit, you just need to ditch lead if *it hits the fan.

copy that. didnt read weight was on a belt.