The beans will soften quicker if they are soaked prior to cooking. According to Camellia Beans, there are three easy ways to do this. I usually use the one-hour quick method. Read about them here.
Liquid Crab Boil is a liquid seasoning Zatarain's and used in boiling seafood in Louisiana. It is concentrated and very potent, so resist the urge to use more than called for until you taste the beans. I have ruined dished before by using a little too much Liquid Crab Boil. It's a unique flavor and cannot be easily duplicated. You can buy some here. Substitute some cayenne pepper to taste if you can't get the Crab Boil, you'll miss the distinct flavor but you'll get the heat.
This recipe was developed using Great Northern Beans, but it can be made with Navy Beans with no change in flavor or even Red Kidney Beans with a very slight change in texture and flavor.
This recipe is best if you can use some homemade shrimp stock. I realize not everyone has some in the freezer, so if you want to make some from the shrimp heads and shells, read this. If not, this recipe is still very good with some commercial chicken stock or seafood stock. Just click those links and buy some.
I recommend not salting your beans until the end. There are a couple of reasons for this and you should check out my article on beans so that you can learn more about it.