How much anchor chain is enough?
You obviously need a lot more anchor chain than 20 feet of chain for an IP 37. There are a variety of rules of thumbs for sizing the minimum amount of chain should be used on an anchor rode. The two most commonly cited are one foot of chain for every foot of boat length, and the other is roughly 6 to 10 pounds of chain per thousand pounds of displacement. So for an IP37 the first rule of thumb would suggest 37 feet of 3/8" chain and the second method would suggest roughly 80 to 150 feet of 3/8" chain. If I were going to the Bahamas where the anchorage tend to be bouncy, have sharp bottom features and be fairly shallow, I would think that 100-150 feet should be adequate. I would think that you could get by with less than 100-150 feet on the southern US eastcoast but as you got into the rockier north east US I would think that you are back to wanting a lot more chain again.