How do you tell how many shackles of anchor chain are in the water?

To determine how many shackles of anchor chain are in the water, you first need to measure the length of the chain that is deployed. One shackle is typically 15 fathoms (or 90 feet). By dividing the total length of the chain in the water by 90 feet, you can calculate the number of shackles. For example, if 180 feet of chain is in the water, there are two shackles deployed.