An apparatus for varying the dimensions of a hull of a vessel comprising an arcuate truss assembly having a plurality of members pivotally joined. The arcuate truss assembly is operatively arranged to form a portion of the hull. The assembly is operatively arranged to extend and retract to vary the dimensions of the hull when the plurality of members are pivoted with respect to one another. The members of the arcuate truss assembly pivot in a plane substantially coplanar with the portion of the vessel hull.