I am currently working on a project boat. 16ft bass boat. While removing the gas tank I notice there was a grounding strap attached to one of the bolts that mounts the tank to the floor. The strap wasn't connected to anything and it is not in the area where the battery is located. There is nothing in the area where it would make sense to attach a ground strap. Do metal tanks have to be grounded and is so, grounded to what.