Abstract: An assembly is disclosed for retaining a boat hull centered on a boat trailer during launching and loading of the boat. The assembly includes a pair of guides each extending upwardly from the rear or loading and launching end of the trailer for engaging opposite sides of the hull and urging the hull to a centered position relative to the trailer. The guides may be covered with polyvinyl chloride to present a smooth, low friction surface for engaging the hull without marring it as the hull moves past the tubes. Lower ends of the tubes are curved inwardly with the vertical sides of the tubes being flattened to reduce flexing of the tubes transversely of the hull. The lower tubing ends are received in a snug fitting channel, with upper and lower faces of the tubes tightly clamped toward each other to expand the flattened sides into tight engagement with legs of the channel.