TOS and TMP enterprise were suppose to be around 300 metered long, and mass 300,000 metric tons. This would make it approximately as long as an large aircraft carrier but three times as massive. I haven't actually worked out the volume of the star ship, but eyeballing it tells me it's a pretty space inefficient design, meaning it has a lot of dimension and surface ares for not much interior volume. The primary hull is on average maybe 3 decks thick. The secondary hull has at most 1/8 the volumn of an aircraft carrier hull. The hull of a large aircraft carrier almost certainly has much more interior volume in total than the TOS enterprise. So, this means overall, the enterprise is an extraordinarily dense structure, far denser than modern ships, planes, or submarines. Possibly 3-6 times denser. Enterprise is certainly denser than water and would sink like a stone if it had to ditch. Since most of the enterprise's primary and seconary hills are empty space just like shipand assuming 2 centuries of progress in material science would allow the ship's structural weight to stay under control, this suggests most of the ship's mass must be in those two big engine nacelles. What do you think?