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.