Do I need more fletching for longer arrows?

[halfseminole]

I shoot a real "clothyard" arrow, 37-38" long.  I use footed dowels or rivercane to get the length right, seeing as I have a draw and a bow capable of 36" all day long.  My anchor point is comfortable at 36", and a full draw pic seemed to confirm my form was correct, I just have a ridiculously long draw.  

But, in order to stabilize my arrows, do I need more feather?  I know the arrows I saw preserved for the style of bow I shoot had a LOT more feather on them-between five and seven inches of feather, three fletched.  I shoot about three inches of feather two fletch, and on smaller arrows they worked fine.  I can still control the arrows, but I'm not as sure with hitting my intended spot with my setup.

I've never shot three fletch before (side effect of learning on reservation) and I'm wondering if I need to change over as well as use longer fletching.  There is very little out there for those of us with long draws.

I did try drawing 30 or 31 inches.  It's not comfortable at all-it's like trying to shoot a kid's bow.  So shooting shorter just doesn't work.  If I get excited or distracted I can easily overdraw a 36" arrow and hit myself in the hand with it, so it's not maxing out there, either.

I read and I read and I read, and I still can't figure out some stuff.  I realize that archery is not often concerned with giants (or their equivalents) but surely someone would know how much fletching they need (ballpark...)

[Whispers Death]

3 (120 degree) 5" Helical feathers will stabilize them. You will; however, need a stronger arrow to go that long or the spine will be weak. How tall are you?

[halfseminole]

6' 4" with what's called marfanoid body habitus, so my arm span is well longer than my height.  It ends up around 7' 4", even with my messed up left shoulder.  The pic of me with my horse bow in the full draw thread was actually taken an inch or so off full, but I can't blame my wife, I was having a bad shoulder day.

If that's what it will take, I will save for a jig.  I learned a lot about the old ways, but honestly sometimes I wish I could just go and buy a handful of finished arrows.  Since I can't, I plan to try and make the best of this.