How far away do you have to be to survive a nuclear explosion at sea?

Imagine that terrorists have stolen a 50KT Russian nuke. They’re transporting it in a modest-sized ship. The Americans, with the help of the Russians, have detected the ship and decide to sink the ship with a missile. As a final act of defiance, one of the terrorists manually detonates the nuke. (How they do this is beyond the scope of this thread.)

How far away do you need to be to survive? Does the degree of swell make a difference? What about the curvature of the Earth?

Brucie bonus: suppose it wasn’t the terrorist that detonated the nuke, but a Russian submarine taking the opportunity to test one of their nuclear-tipped torpedoes under cover of the strike? (Same power, for simplicity.) After all, the Americans know there’s a nuke there and an explosion would be possible. Now the blast is sub-surface. Does this make a difference?

For starters, read here:

Well, it’s not 50kT, only 23, but this was tested at Bikini Atoll.

http://www.history.navy.mil/faqs/faq76-1.htm

You beat me.

The Bikini Atoll tests weren’t really what I had in mind. I was thinking rather of being in a small boat on the open ocean.

Submarines are rather fragile on the surface, are they not?
As for an open boat, the goats on the ships died.

True, but inside an atoll, the ocean swell is very much diminished.

So, how far away would you have to be for the curvature of the Earth to have a significant effect on your exposure?

And what about swell? Say a 3m swell or a 10m swell.

This depends on how far above the surface both you and the blast are.

Couldn’t a nuclear explosion under the sea create a tsunami? If so that could have pretty devastating effects a long way away.

Not really. The biggest nuclear bombs are many orders of magnitude smaller than the smallest of geological events. I did a back-of-the-envelope calculation back when the Indian Ocean tsunami hit a few years ago. I forget the exact number, but the energy released was something like four or five orders of magnitude bigger than the total yield of every nuclear weapon combined.

The earth will shake us off like a bad case of the flu.

Missed the edit window:

Wiki says that tsunami released an amount of energy equivalent to 9,560 gigatons TNT. That’s six orders of magnitude bigger than what the OP mentioned.

What about the crew of the Daigo Fukuryu Maru? They were in a small boat on the open sea, about 90 miles away from the explosion.

Aren’t bad cases of influenza fatal? That is to say, not shaken off at all.

But that was a 15 MT explosion, not a 50KT one.

Fair enough. In my defense, I’ve been living under a rock for the last few days, so I’m only now aware of the whole flu panic thing. So it was a rather unfortunate way to mangle a half-remembered George Carlin quote.

I think you are overestimating the destructive radius of a nuclear weapon. It sounds like you are expecting a crater in the ocean miles across :).

Anyway, according to
http://www.ctbto.org
there have been very few water tests. The only test specifically designed to occur in open water appears to have been Operation Wigwam-a 30kT weapon detonated at 2000ft in 16000ft of water 500 miles west of San Diego. It was a test to determine what would happen to a submarine near a nuclear explosion.

http://nuclearweaponarchive.org/Usa/Tests/Wigwam.html

as you can imagine, the test object closest to the blast didn’t do well, but submerged test vehicles a few thousand feet away, survived quite well.

Fallout is a major consequence of any surface or subsurface burst, but the blast effects are not as great as a comparable air burst. According to what I have read, I am not by any means an expert on this.

My only comment is that when we would do Damage Control drills in conjunction with a simulated nuclear attack, the blast was always “…range ¼ miles” and the wind direction and speed was given. My pay grade wasn’t high enough to need to know more than that, but I always assumed that distance was what had been determined to be survivable for a surface ship.