Im trying to model a floating roof for a storage tank.  The file I included shows the basic structure I would like to analyze.  The entire structure will float, but will be restricted from moving in radial directions by guide poles.  The analysis technique I am using represents the loads (weight, buoyancy, etc.) as pressures on the top of the deck plate, as well as on the bottom of the "pontoon".

I can't seem to find a way to restrain the model.  The entire roof must be free to translate in the y direction, but not rotate or move in the radial direction.

Thanks for any help you can give, I am quite new at solidworks if you cant tell.

Thanks,

David