Abstract: A flat line boom apparatus holds a fishing rod on a boat and guides a fishing line laterally outward from a gunwale of the boat so that the line resists entanglement with other fishing lines also extending from the boat. The apparatus includes a cylindrical sleeve which slides into a conventional fishing rod holder mounted in the gunwale of the boat. The sleeve is secured within the rod holder utilizing a bayonet lock to engage the cross pin of the rod holder. An annular collar is detachably connected to the sleeve so as to allow rotation of the collar about the sleeve. An elongate boom is attached to the collar so as to extend laterally outward from the gunwale of the boat. A fishing line clip is attached to the end of the boom for releasably retaining the line near the surface of the water. The line guide releases the line when a fish strikes. A shock cord extends between the boat and the end of the boom to provide additional support for the boom.