Cressi Travelight surface buoyancy/weight

Hi,

I am heading towards the Zeagle ET (see other thread for more info on the diving we do) for my first purchased BCD.
My wife thinks she may prefer a jacket to a wing and is looking at the Cressi Travelight Lady.

I have read a lot about the buoyancy capacity of BCDs and why you do not want one that is too large. I concur and we are low-weight/good-buoyancy divers. To me the limiting factor on going smaller is when the BCD cannot hold a full tank, regulator bits and any attached weights when dropped in the drink. This thread is about this specific aspect.

The Cressi Travelight Lady in Small has a stated 8.2kg of lift. Cressi Scuba Diving B.C.D - Air Travel Lady
She regularly requires 8kg of weight (compared to me she is more floaty, and wears a 5mm).
So if this 8kg goes in the integrated pockets this rig will sink, no?
Even at 6kg added it would seem marginal that this rig could keep itself on the surface.
The spec of the pockets allows 4.5kg and there are rear pockets that take another 2kg each.
So the lead-happy diving can squeeze 13kg into this puppy and it only has 8.2kg of lift?!?

Am I missing something? I must be? Or do some divers sacrifice surface float-ability for travel convenience?
Please note I am only talking about the fully assembled rig, in the water, on the surface, fully inflated, when a diver is NOT wearing it.

Simon

P.S. I also realise that this thread will head off into belts v. integrated at the drop of weight pouch which is fair enough but not my question.

About the only thing missing from your equation is the inherent buoyancy of the BC itself - which is likely not much, maybe 2kg at most (and that would be a pretty "floaty" BC). the end result is likely the same though, once you add up the negative buoyancy of a full tank, regulator and whatever else may be on your BC (maybe a heavy dive light) That 8kg of weight is likely going to send that BC to the bottom. Even if it just barely floats, that means it needs to be filled to its maximum before it is removed (and who's gonna remember that sort of thing).

Out of curiosity, assuming we're talking about a travel BC for the purposes of warm-water travel, what type of exposure protection is your wife wearing? 8kg strikes me a quite a bit for your "standard" warm water destination with a 3mm fullsuit or less (especially for someone that fits in a small BC).

---------- Post Merged at 10:58 AM ---------- Previous Post was at 10:55 AM ----------

simonknee:

Am I missing something? I must be? Or do some divers sacrifice surface float-ability for travel convenience?
Please note I am only talking about the fully assembled rig, in the water, on the surface, fully inflated, when a diver is NOT wearing it.

Click to expand...

Regarding this last piece - I'd estimate that most warm water divers use little enough weight that it's not a concern (8.2 kg lift is actually very small compared to your average BC) but I'd also bet most don't understand the correlation between the amount of ballast being carried how much lift the BC provides.

CT Sean:

About the only thing missing from your equation is the inherent buoyancy of the BC itself.

Click to expand...

I wondered about this and then wondered whether Cressi factored this in to their figures or not - I imagined that they did since this would make the numbers look better and lift is lift after all.

CT Sean:

most warm water divers use little enough weight that it's not a concern

Click to expand...

I use little enough weight but my wife likes to be very toasty and has a full 5mm O'Neil that you'd never prise off her! This is perfect for her in the Red Sea where we have done most of our recent diving. In fact she often puts another 1mm top on underneath. It might be too much in the tropics but I'd wager not.

Practically should she go for this BCD (or similar) it would seem that the best course of action is to weight the BCD with as much as is sensible to allow self floatation. Then the rest goes on a belt. Yet it strikes me as odd that the unit can hold more weight than it can float!

Simon

Keep in mind that a BC not only needs to float on its own without a "passenger" but also compensate for the buoyancy change due to suit compression and gas carried. I don't know anything about the buoyancy of a 5mm suit (I only have a 3mm and a 7mm) but, depending on tank size, 2 - 3kg of that 8.2 kg lift is dedicated to the buoyancy change of the gas in the tank. That leaves only 5-6 to handle suit compression and that assumes your weighting is perfect. You'll need others to weigh is as to whether that's enough lift for a 5mm suit.

CT Sean:

That leaves only 5-6 to handle suit compression and that assumes your weighting is perfect. You'll need others to weigh is as to whether that's enough lift for a 5mm suit.

Click to expand...

Buoyancy by numbers - Divernet

The buoyancy of their 5mm is 2.64kg. Now this isn't my wife's 5mm but this is going to be ball park and so this BC would have enough spare capacity even if the suit was compressed out of existence. You can see how a 7mm would be marginal to say the least. As you say this assumes perfect weighting.

Thank you Sean I am finding this very useful.

Simon