12 string strings

[Danbgt]

I’m not a great guitar player. I started playing after retirement. I play fingerstyle. Mostly delta blues, John Fahey and stuff like that. I also play mostly in open C. My open C guitar is a Taylor 312ce 12 fret. I acquired a Taylor 352ce sometime back. A 12 string, also a 12 fret, and have recently become gutsy enough to start fooling with it. Tuned to open C the strings are much too floppy. Lots of buzzing and rattling. Can anyone suggest what strings to use to? I had rather not have to assemble a custom set but will if need be.

[Earl]

Dan, the typical twelve string light gauge set for E-e tuning is 47-10 gauge, such as D'Addario EJ-38, as are the Elixir twelve string set.  A 0.047" string is pretty light to be tuned down two whole steps from E to C, hence the floppiness.  You might have to get some medium sets like D-Addario EJ-37 (54-12) and mix and match.  You can find string tensions published here:
https://www.elixirstrings.com/support/string-tension-for-tuning-guitar
https://www.daddario.com/globalassets/pdfs/accessories/tension_chart_13934.pdf

The goal is to keep the individual tensions roughly the same as E-e tuning (most are in the 22-32 pound range) and also keep the total tension for all strings to ~250 pounds or less.  250 pounds is normal for those 47-10 sets at standard tuning, and the guitar can handle that just fine.  Tune 54-12's up to E and you are at 335 pounds of total tension.  My twelve string guitars almost always wear Elixirs.  I don't care much for string changes and a twelve string is worst of all, so I try to make them last as long as practical.  I play in several alternate tunings but always on my six-string guitars.  In fact, some of my guitars are dedicated to certain tunings.  The quickest way to kill the tone of a set of strings is to tune them up and down repeatedly.

[Edward]

Hey Dan,

If you keep that guitar in open C then yes, by all means go to a medium. 
BUT, you better remember you've got mediums and not tune up to standard.  Taylor 12s are designed and braced for lights tuned to standard; you can go medium gauge if tuned down a full step (I did this for a while on a 655 and it sounded great).  So you'll likely be fine with mediums tuned down to open C, esp since your 12F is also the shorter scale.  Try the elixir PBs ...I've used these on my 12er forever and it's a fabulous string.

Edward