A downrigger adaptor assembly includes a seat-mounting member having a helical spring disposed about a support post, engageable with a boat seat. The present invention further includes a mounting plate on which a downrigger base-mounting member is secured, and an elongated cable connected to the mounting plate and a stationary portion of a boat so that the assembly can be maintained within a predetermined path during operating conditions. Such a cable includes quick-release fastening members for allowing an operator to readily adjust the predetermined path as needed.