Thought provoking cartoon clip

[knoodelhed]

from Rocket Power: Island of the Menehune

In particular, please look at the footage between 2:22 and 3:02. The little ones visiting here who saw this on DVD had a few questions, and I developed a couple of my own.

1. Is there a possibility of encountering a vertical current, depending on conditions and topography?
2. Could a freediver in trunks really lose enough buoyancy to keep them from regaining the surface?
3. What depth would that be likely to become an issue?
4. Is this a useful illustration of SWB?

Thanks for watching and thinking.

[island_sands]

Sorry, this video is no longer available?

[billieball]

Interesting video. The part I had great issue with was the fact that the "freedivers" kept their snorkels in their mouths the entire time they were underwater. That would make it difficult to protect their airways in the event of an underwater rescue, eh?

[ILDiver]

They prolly learned skin diving through PADI, so the snorkel stays in.

1) I have heard of vertical currents, though I don't know how strong they get.

2) Yes a freediver will lose buoyancy at depth.

3) The depth varies for every individual. I've never checked my buoyancy in just trunks, so I don't know what my neutral depth is.

4) Short answer is no, I don't think so.

[Bill]

'Could a freediver in trunks really lose enough buoyancy to keep them from regaining the surface?
What depth would that be likely to become an issue?'

Easy to test. Pick an easy depth and have a safety. Dive to the bottom and exhale all your air. Your buoyancy will be the same at any bottom less than 60+ feet. If you sink another 60 feet after you exhale, you could lose a few pounds more (and do a lot of damage). Fresh water can be 5-6 pounds less buoyant.
I've seen a few of these water tests and it's hard to find anyone over -10 pounds (You need very low body fat) and 10# isn't too hard to get moving up.

[ILDiver]

Oops, thanks Bill. I failed to finish a thought on that one. Forgot the "enough buoyancy to keep them from regaining the surface" part. You could lose enough buoyancy that your unconscious body would not make it back, but kicking, you should be able to make it. I've heard it can be difficult at depth to start moving back up toward the surface.

[Bill]

'I've heard it can be difficult at depth to start moving back up toward the surface.'

I remember a few dives at 80-90 feet, my super-soft spearfishing fins, big cannon with reel and 20-24# of lead but even the one where the fin pocket tore out, I didn't have to 'donate' a weight belt.

Now-a-days at double that depth I'll take an extra second or two to get a good pull on the rope and not have to kick two or three times to feel like you're moving.

[mtyvlcro]

Yes vertical currents are a reality. The times I've felt them is by the wall in La Jolla. I was kicking along the bottom (SCUBA) at about 60' and at the edge I bopped down a couple of feet before I knew what happened. I believe the time of year and temperatures had something to do with it. I don't remember the stats on that, but I have heard stories of others who had much worse experiences.