Woman critical after West Van scuba diving accident - Canada

[tonka97]

Thanks John for one of the best posts ever on this board.

This is the type of information, history, and insights I'm looking for when I spend time on the various forums.

 

[TSandM]

What I'm saying is that negative, swimming ascents make precision difficult -- which wouldn't work for me, because I stage all my ascents. They also make it very easy for the diver to end up yo-yoing because they got distracted or ceased to fin for a moment, and sank. You are right that they're probably safer for people who have marginal buoyancy control, but I don't operate in the universe that you do, so I don't pick what I consider optimal strategies based on the idea that people don't have and won't develop better skills.

 

[Crush]

Why would I want to make a swimming ascent (and not a buoyant one) except in the case where, well, my BCD has failed? I am not trying to stir it up here - I have just never thought of swimming up when I can get air to do it for me.

 

[DandyDon]

Why would I want to make a swimming ascent (and not a buoyant one) except in the case where, well, my BCD has failed? I am not trying to stir it up here - I have just never thought of swimming up when I can get air to do it for me.

So you can duck quickly, vertically, if you see a boat or jet ski approaching maybe? We have a thread recently moved from Accidents to some other forum about a diver who saw one approaching, couldn't sink fast enough, rolled over to kick down and lost his legs.

To clarify, I use buoyancy to get to my last stop at 15 feet, then kick up from there later. I like to be able to sink vertically to 15 if needed.

 

[themagni]

Drownings after surfacing without establishing buoyancy have been all too common on this forum; my bud & I drill on oral inflating and dumping every trip just in case panic tries to take over one of us in such a case.

About a year and a half ago, TS&M posted about that experienced diver from Oregon who floundered on the surface after an OOA ascent and drowned. Since then, I've practiced oral inflation on every dive. I explain why so my buddies don't think I'm in serious trouble, but I haven't seen anyone else start doing it.

halemanō, I haven't done the math for cold water, but the diver was in the Pacific Northwest. Since she was new to diving, she was likely in a 7mm wetsuit (possibly two-piece) rather than in a drysuit. Your numbers might be correct - perhaps at 33 ft she should be "slightly negative" in a 7mm wetsuit. However you live in Hawaii (I am envious, by the way...). Have you accounted for the difference between a 3mm suit and a 7mm suit? I have got to tell you that I LOVE Florida diving since I feel light as a feather on the boat and my buoyancy rocks when I don't have to contend with 7mm x 2 or a drysuit...

Diving in August in Vancouver would be in a 7mm John & Jacket or drysuit, but probably the J&J -- 14mm on your core -- plus hood, gloves, and boots. You simply cannot dive in anything less than a full exposure suit up here, end of story. The beaches here will be full of people on a 30C day, but the water itself will be almost completely empty. Water surface temperature is about 7C, with thermoclines dropping that to 4C even in the summer. We were just talking about this at work -- every year a tourist thinks "I can swim that". They get a nice tour of a Coast Guard vessel, free hot chocolate, and a reminder that the water here is a lot colder than it looks.

That much suit would put her... ballast somewhere around 35#, depending on her BMI. I wear a neoprene drysuit, even in the summer, with 30#, and I'm a 165#, 5'11" man. If she was new to diving, they'd likely throw an extra 5# on her and if she hasn't done a buoyancy check she might still be at her "starting" weight guessed at when she took OW. (So easily up to 40# of lead, which would be a perfectly reasonable amount for diving here. One of my ex-buddies dives 40# in Victoria and 6# in Florida.) The two most likely weight configurations would be to have 10# in each of the integrated pouches (with the rest unditchable) but most likely all the lead on a ditchable belt. We practiced ditching when I took OW, and my instructor told me "If you ever wonder if you should ditch your weights, ditch your weights. Come find me and I'll buy you new ones."

That might be moot, as the news said she didn't make it to the surface. However, I've been in the paper and they always get something wrong.

 

[themagni]

Why would I want to make a swimming ascent (and not a buoyant one) except in the case where, well, my BCD has failed? I am not trying to stir it up here - I have just never thought of swimming up when I can get air to do it for me.

As you ascend, your rate of ascent will increase as the gas expands. You're already neutrally buoyant so swimming upwards will make you go ascend. As you do so, the air in your cells (BC / drysuit / lungs*) will expand, giving you more gas volume. As you go from 66' to 33', the volume of gas you've got in your cells will increase to 150%. As you go from 33' to the surface, that volume will double, so a total of triple what it was at at 66'.

Thus, if you're comfortably finning along at 60' you have to release gas to remain neutrally buoyant at 30' and at 15'. This means you actually have to vent slightly when ascending to maintain an even rate of ascension.

*overpressure valve not standard configuration.

 

[tracydr]

Why would I want to make a swimming ascent (and not a buoyant one) except in the case where, well, my BCD has failed? I am not trying to stir it up here - I have just never thought of swimming up when I can get air to do it for me.

PADI teaches a negative swimming ascent to prevent uncontrolled ascents. It's hard for new divers to control the amount of air they add and subtract to their BC accurately enough to avoid rocketing to the surface.
I do a negative ascent when lightly weighted. If dressed heavily and diving deep I might use a squirt of air to get started and then dump it as I get shallower. I'm usually pretty neutral at the end of my dive except if I only used half a tank or less.

 

[Crush]

As you ascend, your rate of ascent will increase as the gas expands. You're already neutrally buoyant so swimming upwards will make you go ascend. As you do so, the air in your cells (BC / drysuit / lungs*) will expand, giving you more gas volume. As you go from 66' to 33', the volume of gas you've got in your cells will increase to 150%. As you go from 33' to the surface, that volume will double, so a total of triple what it was at at 66'.

Thus, if you're comfortably finning along at 60' you have to release gas to remain neutrally buoyant at 30' and at 15'. This means you actually have to vent slightly when ascending to maintain an even rate of ascension.

*overpressure valve not standard configuration.

Yes. I didn't state it explicitly, but I do vent air as I rise. Since I wear a drysuit with heavy undergarments and sometimes dive below 100 feet, if I didn't vent air I fear that I might go into low earth orbit.

My question as to why one would choose a negative swimming ascent was answered by DandyDon - thanks DD.

 

[MXGratefulDiver]

PADI teaches a negative swimming ascent to prevent uncontrolled ascents. It's hard for new divers to control the amount of air they add and subtract to their BC accurately enough to avoid rocketing to the surface.

Actually it's not ... you just have to have them practice it.

When skills are practiced multiple times over the course of the checkout dives, new divers rather quickly develop a "feel" for how much air to add or release as they are changing depth. I will not pass an OW student until they can ascend ... and hold a stop ... without the need to kick. It's really not that hard ... it just takes practice.

... Bob (Grateful Diver)

 

[sabbath999]

Since I wear a drysuit with heavy undergarments and sometimes dive below 100 feet, if I didn't vent air I fear that I might go into low earth orbit.

Yeah, I personally don't want to look like an ICBM launching either... especially since I am still gaining experience in my drysuit. I keep it pretty "squeezed" going up, although I am not going to want to swim hard enough to exert myself at depth.