The Bartels system is a reefing system, though you could use the drum and swivel without the rest and save some money. See a/o this thread: http://wayfarer.org.uk/forum/viewtopic.php?t=509&highlight=bartels.
Somewhere I must have a detailed drawing and part list for the Bartels system. Unfortunately Uncle Al has not yet added it to the WIT site. Contact me off list and I’ll send you the files.
The “Bartels” information is also available on the UKWA main web site and on Dave’s site (see links on WIT). The article was also published in W-News a couple of months ago. And finally; use this forums search function for more information on the Bartels system.