Molecular dynamics simulation studies on the structure, energetics, and dynamics of an all-meta-phenylacetylene oligomer in helical and coiled conformations in water have been performed in order to understand the physical basis of helix stabilization in water. It has been demonstrated that the oligomer maintained a dynamically stable helical structure in aqueous solvent at room temperature, without intrachain H-bonds, in agreement with experimental observation. The structure obtained from simulation is found significantly different from the structure presented before based on energy minimization only. The average structure of the helix from dynamics simulation has been characterized in detail. Comparison of energetics between the helical and coiled conformations of the oligomer demonstrated that, in addition to the solvophobic effect, the self-energy of the oligomer also provides a substantial preference toward the helix structure due to favorable van der Waal interactions. No water bridge stabilizing the helix was found. Interestingly, the helix represents a novel model double-walled nanotube DWNT). Although the inside surface of the helix pore is dominantly hydrophobic in nature, water-molecules are allowed to enter into the tube during dynamics but no permeation of water through the tube was observed over the 0.75 ns trajectory. The water molecules inside the hydrophobic tube were found to be strongly H-bonded among them with long lifetimes. The overall dynamics of water inside the tube was quite different from that of water molecules in the bulk.