Create overlapping "core" for vessels.
Technical short: just apply the XSLT to the xml of a vessel; all blocks are moved into alignment with root block on the z-axis Obiously; the result, if you have made all blocks of the same size; is a complete overlap of all blocks.
The XSLT,together with ship xml can be pasted into: http://www.purplegene.com/static/transform.html
License: GPL 3 affero Rationale for license: if you modify the XSLT or use it as a service; then distribute the modified XSLT.