Sudden ascent with SeaQuest Libra BC ???

[TurtleDivers]

Help please! My wife & I are experienced divers in tropical areas but new to Northern California cold water diving. On 2 recent dives in Monterey she experienced very sudden ascents due to rapid increases in bouyancy that has us extremely unsettled.

She uses a SeaQuest Libra model BC, a back bladder design. It's never been a problem in warm water but we're wondering if the BC may be unsuitable for cold water use. At 40ft, it seemed to take a lot of air to provide adequate neutralizing lift. Then as we gradually moved higher to 30ft, it seemed to rapidly increase it's lift in spite of bleeding off air from it. She carries 30lbs of weight in it which, I believe, is near it's limit. I wear a jacket-style BC and while I noticed an increase in lift through the same ascent, it wasn't at all as abrupt or difficult to manage.

Is anyone out there familiar with the expected performance of the Libra (similar to the Men's "Balance") in cold water or similar back bladder designs? Is its use in cold water pushing its performance limits? (. . . or do we have some other cold water training issues to deal with??)

Thanks for your advice.

 

[Snowbear]

Has she changed anything - exposure protection and amount of weight perhaps?

 

[bwerb]

Hmm...I'd do a weight check.

What exposure suit is she using? (wet or dry)...if dry...is she using it for bouyancy control at all?

I'd also suggest perhaps staying "ahead of the curve" as it were on the ascent...dump gas earlier than you think as you ascend and don't be afraid to dump some significant amounts if it's getting away on you a bit.

 

[LUBOLD8431]

I never had any problems diving in cold water with the Balance BC. I used it for almost four years. I think its operator error, most likely. Try using the pull dump (on the lower right of the BC), instead of the power inflator to dump air out of the BC.

 

[TurtleDivers]

Thank you all for the inputs. To answer your questions:

The exposure suit is wet. As noted, these have been our first CA dives. We've used 3mm in the tropics but 6.5mm+6.5mm in CA so obviously a lot more wetsuit weight and bouyancy to deal with. This happened both before and after a weight adjustment, the before being a case where she was definitely a little over-weighted and the after appearing to be a good weight throughout until the beginning of the ascent.

I understand about 'staying ahead of the curve'. My observation, however, was that her BC has a much steeper reaction curve than mine. Maybe it is just operator error or getting accustomed to the farmer-jane . . . but it didn't seem so at the time.

 

[ScubaSarus]

I'de suggest she is too overweighted. Unless the BC is malfunctioning (sticking inflator) I would also suggest you get more dive experience for her. It sounds like she hasn't done a lot of consectutive diving and only dives once in a while. If it really concerns you go and take a peak bouyancy course (very quick lessons) and the instructor will be able to tell you exactly what the problem is. This is a characteristic of a divers who just want to get down to the bottom and haven't had or spent the time to fine tune their weighting. So they just pile on the weights. It takes a lot of work logging and weight checking to get it right with diff gear configurations.

 

[ScottyK]

Turtledivers- I think the main problem is the two 6.5 mil layers. With 13 mils of thickness around her, it's no wonder she's getting vastly different buoyancy characteristics at different depths. The wetsuits are compressing, and losing buoyancy as she goes deeper.

The "slow reaction time" of her BC is due to having 30lbs of lead with all that compressed neoprene. The first thing you need to do is lose the extra suit, and try to get her closer to 15lbs of weight. Trapping a layer of water against your body is how wetsuits keep you warm. She's not getting much extra thermal benefit from wearing a two piece. I would go so far as to say that she's at increased risk of a dive accident if she contiues with that configuration.

My lady hates the cold, and is able to dive in the northeast with a one piece wetsuit and lycra skin. She stays comfy into the mid 50's and can handle 50 degrees if it's not for an extended period. With her BP/Wing, she needs 4 additional lbs for a "total" of 11.5 lbs of weight. When we first got certified, my LDS sold her one of those POS Farmer Johns, and she had issues similar to your wife (not as drastic though). I knew something was wrong when she needed more lead than I did. At 220lbs, I weigh twice what she does. We picked her up a nice fullsuit with wrist, neck and ankle seals. She finds it's actually "warmer" than the FJ was.

If a single wetsuit proves to be too cold for her at certain times of the year, let her dive where/when the one piece is enough until she gets more experienced. You could then consider getting her fitted for a good quality drysuit.

 

[japan-diver]

Turtledivers- I think the main problem is doubling up to 6.5 mil wetsuits.

Although the changing from a 3mm to a two piece 6.5 does take some getting used to there is no problem with this set-up. Many divers use this suit and I have seen some thicker than this. Overweighting may be a problem, with a thick suit a very slow descent at the beginning is normal as the suit will begin to compress and the descent will continue.

Practice in shallow water with buoyancy control and stay ahead of the curve as others said. Also as divers change to a rear inflate BC they must get used to using the pull dump on the rear of the bladder dump. Depending on design either on the bottom left or right. Assuming no functional problem with the BC the resulting ascent was user error but easily corrected with practice.

 

[jhelmuth]

Turtledivers- I think the main problem is doubling up to 6.5 mil wetsuits. With 13 mils of thickness around her, it's no wonder she's getting vastly different buoyancy characteristics at different depths. The wetsuits are compressing, and losing buoyancy as she goes deeper.

The "slow reaction time" of her BC is due to having 30lbs of lead with all that compressed neoprene. The first thing you need to do is lose the extra suit, and try to get her closer to 15lbs of weight. Trapping a layer of water against your body is how wetsuits keep you warm. She's not getting much extra thermal benefit from wearing two. I would go so far as to say that she's at increased risk of a dive accident if she contiues with that configuration.

My lady hates the cold, and is able to dive in the northeast with a one piece wetsuit and lycra skin. She stays comfy into the mid 50's and can handle 50 degrees if it's not for an extended period. With her BP/Wing, she needs 4 additional lbs for a "total" of 11.5 lbs of weight.

If a single wetsuit proves to be too cold for her at certain times of the year, let her dive where/when the one piece is enough until she gets more experienced. You could then consider getting her fitted for a good quality drysuit.

Agree. The compresion of that much neopreen is significant. Consider a drysuit, or gain more experience with the BC (the choice of BCD you choose will not be the issue since Boyles law is oblivious to what bladder is used).

 

[ScottyK]

Although the changing from a 3mm to a two piece 6.5 does take some getting used to there is no problem with this set-up. Many divers use this suit and I have seen some thicker than this. Overweighting may be a problem, with a thick suit a very slow descent at the beginning is normal as the suit will begin to compress and the descent will continue.

She didn't switch to a 6.5 mil suit. She switched to a two piece suit at 6.5 mil per piece, or 13mil. The issues she's having are identical to the ones my lady had. It's worse if you're a smaller person.

A single 6.5 mil or 7mil is actually what I suggested she switch to.