I'm fairly certain that the hull is 18' long LOA, unless the '18' in "Hobie 18" is nominal only. I don't have the dimensions of my hulls handy, but the link below is a good source of some information. The keel templates file includes dimensions for hull depth and the overall keel shape, but not beam or length.
Also, the weight of the hulls vary greatly depending on when the boat was built, and has been the topic of much discussion on these forums. I believe the "red line" hulls from the mid-80's were some of the lightest hulls ever build, and I heard someone say that theirs weighed in at ~93-94 lbs. My hulls are from '79, and supposedly the resin in the fiberglass and the glue was applied much more liberally on these older boats. The keels were also solid FRP construction instead of sandwich construction, allowing for much greater strength at the cost of additional weight.
What's your interest in these hull dimensions?
'79 freshwater H18