Frozen product should be thawed slowly under refrigeration.  Try to thaw on an as needed basis and keep chilled until use. Do not refreeze crab. The best way to thaw frozen Dungeness crab  is to put them in the refrigerator overnight (at least 8 hours). The exact time can vary depending on several factors like the temperature of your refrigerator and the size of the crab or clusters. However, a general rule for thawing seafood in the refrigerator is about 24 hours for every 4 to 5 pounds of product.