If it's your goal to add new vessels to SH4, I strongly urge you to read through this thread:
http://www.subsim.com/radioroom/showthread.php?t=111177
before you get started modeling new vessels. At the current time, it is not possible to add new vessels to SH4 until we find a way to create SH4 .dat files, a project that is being currently worked on by Skwasjer and his S3D utility. There are a number of "support" files that have to be created along with the model as well.
Not to throw a wet blanket on your enthusiasm, just wanted you to know...
