He let it go over the side and then made it fast to a ring bolt in the stern.
他把钓丝从船舷放下水去，将上端紧系在船梢一只拳头螺栓上。
英语百科
Ring bolt
A ring bolt is a bolt with a captive ring on one end and threads on the other end. The ring bolt differs from the eye bolt in that in the former the ring is articulated, such that it can rotate in at least one axis, and can thus reduce bending forces on the bolt when loaded and will present the minimum obstruction when "flat".