The current world record for depth while holding one's breath and free diving is 214 meters. [link] Although that may be incorrect as there are many listed and that's just the deepest I found.
Whatever the actual depth record is I think that the same individual currently holding that title, (and several runners-up) could shatter the world record by simply first coating the surface of the water with Lycopodium powder before entering it. [link2]

This would render both the diver and the weighted sled to become hydrophobic and plunge downwards at up to 30% faster than without... based on descent differences between a steel ball and an hydrophobic steel ball of the same weight.

I don't think that this would be cheating as they already use a weighted sled and then assistance to return to the surface so helping descent shouldn't be disallowed.
-- 2 fries shy of a happy meal, Aug 24 2024

Breif history of free-diving. https://www.bigblue...iver-ever-dived-is/
22 minutes holding one's breath? Are you shitting me? [2 fries shy of a happy meal, Aug 24 2024]

Lycopodium powder. https://en.wikipedi...i/Lycopodium_powder
It's not just for pyro's anymore. [2 fries shy of a happy meal, Aug 24 2024]

Even longer https://www.youtube...?v=4NJko3CIMl4&t=7s
24 min 37.36 sec, achieved by Budimir Šobat (Croatia) [bhumphrys, Aug 25 2024]

Shallow water blackout https://en.wikipedi...llow-water_blackout
Could even happen in a bathtub. [minoradjustments, Aug 25 2024]

Sub-sea speed demon; 230mph https://en.wikipedi.../wiki/VA-111_Shkval
Bubbles used to reduce drag. [minoradjustments, Sep 17 2024]

Wait, so you can use any equipment or artifice to dive as long as you're not in a submarine or using breathing apparatus?

So you could theoretically strap yourself to a torpeedo aimed downwards then flip it around? What are the specific rules or limitations if any?

[+] for an interesting concept despite my confusion.
-- doctorremulac3, Aug 24 2024


I'm pretty sure it needs to be a free fall, and that the optimal weight sled has been figured out for drag vs. surface area, but being hydrophobic would change all that.
-- 2 fries shy of a happy meal, Aug 25 2024


The diver gets a big lungful and grabs a weighted slider on a cable. No mechanical impulse besides gravity can be used except if you want to lose the contest and try to flipper your way down to record depth.

A buoyancy compensator or life vest is blown up at depth to bring the diver back to the surface. Spotters along the wire watch the descent and the ascent. Their chests compress massively. Marine mammals' ribs have evolved to collapse efficiently to allow the reduced volume.
-- minoradjustments, Aug 25 2024


So... no rules about hydrophobic substances, just as long as it is a free descent.

Okay then.

I can swim an Olympic swimming pool underwater on a single inhalation.
I've even figured out how to mentally slow my heart rate.

How the hell does a human hold their breath for 22 minutes?!

What kind of insane training culminates in such an ability?
Three minutes without oxygen and most brains start becoming irreversibly damaged yet you can train to hold it for twenty plus minutes?...

That's some next level shit.
-- 2 fries shy of a happy meal, Aug 25 2024


"a little bit crazy" Mr Šobat.. er yes
-- bhumphrys, Aug 25 2024


[2fries] Evidently there are many classes of "free dive" records. With and without fins and no cable, same with cable, weighted cable, etc.

The brain is never without oxygen (obviously, or you would die). Interestingly, the biggest danger is not from the compression of the lungs, but from the decompression while surfacing which lowers the partial pressure of Oxygen in the blood vessels as pressure is released into the lungs. The brain is then starved as oxygen (and dissolved air in general) rushes back to the lungs. This is known as "shallow water blackout" and all free divers are at risk, no matter how deep you dive. The longer you stay under pressure the more air is compressed into the body from the lungs, and as you surface and the oxygen depleted air flows back to the lungs, you black out. I saw this happen to a very accomplished free-diving spearfisherman. Coming back to the surface after a dive of only 10m, he stopped moving at a depth of 10' and drifted deeper. We grabbed him and swam him to shore. He didn't know what had happened and thought we were screwing with him until his buddy told him that he was 4 minutes from dying.
-- minoradjustments, Aug 25 2024


My personal best back in my freediving days, forty seconds at forty feet with a speargun.
-- normzone, Sep 02 2024


[norm] I could manage 65' with just a little loiter time. It's very deceptive when you feel so good at depth; you know you are in a sweet spot but don't tarry and always have a buddy watching, because it will change as you surface. I dove with a guy who made 65' look easy. He spotted me and I was confident to try to go deeper because of his overwatch.

We usually dove once to depth to scout and plan, especially for ledges and caves, and then with bad intentions for the kill. After 2 drops to 50'+ you hopefully can bring home dinner.
-- minoradjustments, Sep 17 2024


[2fries] The Russian Shkval torpedo achieves release from the drag of surrounding water by bubbling a shroud of air from the nose and essentially letting the thing fly through the moving air pocket that's created.

I wonder if your idea of using a hydrophobic substance would work for these explody things we love so much.

Or if bubbles from the bootees would allow a faster drop.
-- minoradjustments, Sep 17 2024


If you aerate the water REALLY aggressively you could "dive" at 120mph.
-- bs0u0155, Sep 17 2024


We need to go deeper...
-- 2 fries shy of a happy meal, Sep 18 2024



random, halfbakery