How long to cook dungeness crab?

I agree with the steaming method above. When you are using a camp stove or boat stove, boiling a huge pot of water takes too long. I've got three in the steamer now (trying it with seasoning, onion slices and a splash of wine as recommended above). Aiming for about 10-15 mins.

Woo-hoo! Too late to offer you advice I'm sure, but for the rest of us: We're transplanted Easterners so we eschew the usual West Coast tradition of buying our crabs already cooked. I just got home with my first (live!) crabs of the season. I'd say 15 or even 20 minutes is more like it than 12, especially if you have several in the pot--they are pretty big and dense compared to a lobster or, even more, to a blue crab. Hope you had a great dinner, our's is coming right up!

I normally steam them alive for about 20 minutes and then let them cool for 5 more before digging in.

I live in Dungeness country (pacific coast). We buy one per person and have the fisherman kill-and-clean for us.
Put an inch of water in your crabpot with some onion slices, little bit of Old Bay, and a big splash of white vermouth.
Steam until the legs go rosy red...about 12 minutes for our pot size.
Serve with a nice dry white, Caesar salad with Italian anchovies. Crusty bread.
At our house, dessert is usually another half a crab!

Thanks!! They are still alive.

Where they live when you bought them? And are they still alive? About 15 mins.
If they were not live and look red on the shell...they've been cooked and flash frozen.
Then you just need to rewarm them in the water---about 5 mins.
The steamed and flash frozen are the ones most sold...unless you got them while they're moving.
In either case...save the shells an return to the broth and simmer a bit for a seafood stock for chowder etc.