Abstract: A small, wave-following, relatively stable marine buoy designed for floating at the surface of a body of water and for carrying data measuring equipment. The buoy comprises a buoyant hull member of substantially cylindrical configuration of relatively small axial extent, a mast, and a keel. The keel comprises a spar and a ballast weight attached to the spar. Both the mast and the keel are guyed to the hull at opposite ends thereof, and supported thereagainst by couplings which do not transfer bending moment between the hull and each of the mast and spar.