I suspect he's asking how crewpersons would get from the Saucer to the secondary hull, rather than how did you draw it. Though I may be wrong... --Alex
In that case, I would posit via a Jeffries tube in all likelihood. The Oberth class has the same issue.
Yesh. The 3D Oberth I use, and posted a few times here, corrects that problem with putting in a 'neck' between the top and bottom pieces.
The ships of the Andrew Carnegie class owe their very existence to the philanthropy of Carter Winston. Considered by many to be the foremost businessman and philanthropist of the 23rd century, he made and subsequently gave away multiple fortunes to assist Federation colonies and others who found themselves in need. Winston disappeared in 2264, lost in space and presumed dead. He was rescued by the starship USS Enterprise in 2269. Upon his return to Federation society with his fiancee (later wife) Anne Norred, he once again threw his considerable talents and resources into efforts to help others. As part of those plans, he purchased a significant quantity of surplussed Starfleet equipment and starship hull components and used them to construct a purpose-built class of vessels that could serve a wide variety of needs with relatively simple internal modifications. The five ships of the Carnegie class, all named after famous historical philanthropists of Earth's past, became a common sight in and around the frontiers of Federation space. Willing to go wherever and do whatever was needed, they achieved the notable distinction of being the only Federation-registered ships allowed relatively open access to both the Klingon and Romulan spheres of influence. The class is still in service as of 2367, having been refit internally several times over as the Winston Foundation continues its non-partisan mission of providing aid and comfort to whoever may require it.
My only nitpick with the Longshoreman is to have the containers attach with standard container docking plates so the containers could be swapped out. Some of your others are using containers as integrated hull components but this one looks like it could still work with detachable containers.
Nice to see Bob Ballard get a ship. I've been using his name on shuttlecraft on my schematics for a while.