How cold is your water? I know that I get cold almost immediately... Here's a good link to info about cold water hypothermia. http://www.seagrant.umn.edu/coastal_communities/hypothermia

20 minutes in low 50s? I definitely believe it.

From lifeguarding I had always learned that water doesn't have to be that cold to induce hypothermia, only cold enough to start drawing energy from your core temperature after awhile. I had that academic knowledge put to the test once while sailing with some friends in Casco Bay, Maine, on Memorial Day Weekend of 1995.

We were sailing near a small island where another group of our friends were hanging out on the beach. One of the guys on the beach - ironically, our EMT where we worked - thought it would be funny and silly to swim out to our boat, about 100 yards offshore. He was a capable swimmer. No more than 4 average pool-lengths, most of it shallow. The water was about 50 degrees.

He ran in and then dove in when it was deep enough and started swimming. We were laughing at him. Within just a few seconds, though, his stroke started to look clumsy. He started splashing and flailing. Then we heard him cry "I'm losing strength. I can't swim."

We weren't sure what was wrong but we did a man-overboard manoever and reached out to him with the boat hook. HE managed to grab it, and we pulled him in and dragged him aboard. He was imobile and white, almost blue at the extremities. He was completely chilled through and had no coordination in his hands and fingers. He would have been in serious trouble had the boat gotten there any later.

It was a real lesson to me about the power of cold water. After we warmed him up (he spent the day rolled in blankets with a hat on and repeated administrations of hot beverages until finally stopped shivering and became normal again), he said that what happened was not that he felt terribly cold, but that the water just "robbed his strength" -- the warmth leaving his arms and legs left them numb and useless, unable to exedcute kicks and strokes enough to keep him afloat.

Oh, also, this guy was about 28 at the time and in good health.

Huh. I'm surprised because even on a nice hot day in the summer the water gets to be MAYbe 60 degrees and people spend hours in it. I'm good for about 1.5 or 2 if I don't have a wetsuit on. With a wetsuit I'm good for 4-5.

Here's a chart of the temperatures. Looks like August average temp is 55F for Bodega Bay, which is the next bay north of where this guy was- really close.

Well, I guess I should be more careful than I have been, then. I never realized 20 minutes could do that around here.

cool chart, mightshould! Though it seems to indicate he should have been okay for another 10 minutes or so.

Everybody is different. I used to have a very high tolerance for cold water (Lake Superior in early summer for example) I could be in it for a long time but my brother couldn't handle it for more than a few minutes. We were both pretty much the same size at that point, I may have been ten or twenty pounds heavier.

My sister and I would swim in the Alaskan ocean all summer long when the air temps were between 50 and 70 degrees F. Stupidity of youth and such. I can't imagine a 69-year-old doing the same thing.

small_ruminant, Off Topic:
1. Do you walk/bike to where you are ocean swimming? I’ve often thought of going to the beach here on the east coast and swimming. But, I’d have to drive and have no clue what to do with my car key – it’s one of those stupid electronic ones that I cannot put into a wetsuit pocket. How do you deal with it?
2. And, I’ve always been swimming with the fishes out in the ocean blue (scuba) and don’t relish swimming near shore at dusk/dark where the sharks feed. Sharks are fine out in the deep, but go for the bait fish near shore….do you have any concerns where you are?

mightshould: maybe you could get a small dry bag or OtterBox or something, then put the key in that? I don't know how big a wetsuit pocket is, so this might be a bad idea.

IIRC, water drains heat from the body at some insane multiple of the rate at which air drains heat from the body.

So any water temperature below, say, 85-90 degrees is going to hit you eventually and hit you pretty hard.

mightshould- I just leave my keys in my grocery bag on the beach with my towel. I've never had trouble.

Sharks- we mostly have great whites and they like to eat from below. As I understand it, they don't tend to snack in the shallows. No promises, though.

There are a lot fewer sharks down south, around Santa Cruz.

I've been trying to find that Excel file with all the shark encounters across the globe but it doesn't look like you're allowed to download it anymore- is that correct? Weird, if so. I just downloaded it a month ago, if that. It was very cool.

The thing about Great Whites. They mistake surfers for seals, and after one chomp, they generally realize you aren't a seal and go on their way. (Of course you may die from the one chomp.)

Tiger sharks, on the other hand seem to like us as food.

Ah, our sharks are usually sand tigers and they feed sometimes in the shallows at dusk when the bait fish come in. All the recent attacks here have been on tasty tourists frolicking in the waves around dusk... not frequent attacks, but the time of day is my concern.

I've been diving with sharks around and they pay no attention to wetsuited divers...but, I'd be out there alone at dusk/night-fall after work.

where are you?

I read that the great whites that attack people are pretty much all teenagers- they haven't figured out that surfers taste bad. There WAS one SCUBA diver who got it a couple years ago, up at Mendocino, but that's so rare it really was the talk of the water-obsessed community.

Oh, I'm on east coat - Carolina. But, they don't eat tourists, much.... come on down!
/joking...

I do think sharks don't go for wetsuits - but in the shallows, they can mistake a person for fish. They aren't big bad man-eaters and all, it's just mistaken identity.

s_r, here is an interesting piece.

I hear bull sharks wander up rivers for miles, snacking as they go. We don't have bull sharks, thank god.

I refuse to watch Jaws.

My mom and my dad are both 70. My mom is still working, active, and literally has been told she looks 20 years younger. My dad has been "retired" for over ten years and, apart from the Alzheimer's issues I occasionally mention, is proving to be his mother's son. At the slightest chill or "plumbing" issue he takes to bed and complains (and summons everyone for the questions he can never think of when he's up and about).

I can hardly imagine my dad lasting five minutes in ocean water. He would just give up. Sad but true.