This file is in the PCC directory and remains constant (in most cases). When using a custom universe, it may be changed and placed in the game directory. PCC will then use that file. HULLSPEC.CC contains a record of variable length for each hull (105). That records describe additional hull features. Note that this information is used only to display in the "Build Hull" section and ship mission screens ("Cloak"). They don't affect the real ship behaviour, the host uses its own information. It can lead to problems if a "normal" ship has the "Clock" bit set here, and the PCC interface is used to set the "Cloak" mission. It depends upon the host if the ship will cloak: older THosts will do it.
If you use customized HULLSPEC.DAT and TRUEHULL.DAT, this file may be edited with CCSHIPS, or generated algorithmically using HULLGEN.
This file is obsolete since PCC 1.1.12. Those get the short names from NAMES.CC, and read HULLFUNC.TXT / SHIPLIST.TXT for ship functions.
Each ship record has the following structure of variable length: +0 n BYTEs Short name of the hull, a Pascal String of max. 12 chars. (for use in ship lists, e.g., "Nocturne") +n WORD Special capabilities of the hull: Bit 0 Cloaking Bit 1 Hyperdrive Bit 2 Gravitonic Accelerators Bit 3 Bio Scanner Bit 4 Alchemy +n+2 m BYTEs Special capabilities that didn't fit into the above WORD, a Pascal string (e.g. "Chunnel"), for Alchemy ships a description of the reaction.