Abstract: A boat trailer including a main frame (4,8) having mounted thereon a keel support (21) adjustable, side supports (20) and self-storing upwardly and outwardly flaring dolphins (22). The trailer is capable of being located in water deep enough to float the boat on or off because the tongue is extendible, box beam (70) including hitch (76) is movable relative to box beam (10) under control of powered drive means (74), controlling flexible members (80,84), the opposite ends of which are anchored to box beam (10). A floating boat is guided into an automatic latch mechanism by guides (18,30) and automatically secured to or released from latch (48) from the helm of the boat.