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Comment by nawgszy | Hacker News Reader

I think about this sometimes. Ground, I have no answer, you seem like you will die. Perhaps landing legs first allows you to use those as a crumple zone.

Water, though, isn't the pencil dive the clear winner? Everything else would decelerate you so much faster that it would be bound to cause injuries. The only downside (relative to all other methods of impact) I can imagine is how far underwater you might end up.

I would be happy for someone to tell me otherwise, but this is my completely theoretical summation of a terminal velocity water-landing.

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We were taught the sailor dive, which is good to about 90', according to training. You use it to abandon ship. Err... I was in the Marines.

Basically, cross your legs, point your toes, cup your testicles with one hand, and cover your nose with the other.

The force of hitting the water will crush your testicles and rip your nose off your face. So, you cover them. You cross your legs to keep them together. You point your toes so you don't shatter your feet, ankles, or legs.

When your feet hit the water, immediately bend at the waist. You're going fast enough that you're completely in the water. You fold at the waist to make your depth more shallow. You then flip and swim to the surface.

This works at greater heights but survivability goes down at about 90'. You can practice at lower heights, if you want to learn it. I'm sure there are videos and whatnot.

I believe I read that you want to clench your butthole as well (in addition to covering nose and mouth) to prevent the force of water rushing up your cavities from killing you. Certain pants fabrics help prevent this from happening as well.

Well, sort of. I don't recall that being specifically mentioned but we were taught to tighten all muscles. You actually want to be as tense as you can when you hit the water. You want to hit it as close to straight as you can.

When you do hit it, just relaxing will fold you up - by the way. You're going so fast that you won't relax before you're completely submerged and slowed. I forget the numbers but it means your dive is more shallow than if you'd stayed tensed. There's a ratio for it, but I've long since forgotten.

I suspect there's been a bit posted about this. My enlistment was a long time ago but I'm told they still teach it. There may be some modifications to it, or new data for survivability.

yeah, I've heard people say "at high speed, hitting the water is like hitting concrete", but that's clearly not true; otherwise you wouldn't go underwater at all.

Late reply, but that isn't true. If you a heavy object hits concrete it will go through the concrete, just like it would go through water. In the case of a human, it will potentially crush every bone in the process, but you will still go through it if the kinetic energy vs binding energy is in the right balance.

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