Abstract: A relatively inexpensive, mobile type of offshore structure has truss-type legs constructed of smoothly cylindrical chords and braces whereby the portions of the legs exposed to wave and wind forces, when the unit is in operation, are practically free of the usual turbulence-producing protuberances and recesses. The legs are powered to move vertically in relatively large guides which are pivoted to the support platform. Wedges may be operated to tilt and/or hold the legs in desired slant position as the legs approach bottom. Also, as the legs approach bottom, they are released from the platform and their rate of descent is sharply increased so that all legs will impact the bottom at substantially the same time. The leg slant holding wedges are released as the legs strike bottom so that the platform is free to rock, rise, and fall independently of the legs, under wave action.