I recently redocumented my vessel. It has to be done every year, and is a pretty straight forward process. The form you will need is a USCG form # CG-1258
This is a 4 page form, although you only "mail" (yes you have to snail mail) the first 3 pages. The 4th page is only instructions to you on how to fill it out correctly.
The current fee is $84 for the recording of the paperwork, and a $8 processing fee. So $92 total.
If you wish to write to the USCG documenting section/department it is :
NVDC (National Vessel Documentation Center)
792 TJ Jackson Drive
Falling Waters, WV. 25419
good luck....fair winds....