Does adding more fletching slow the arrow down?

It does, and the Committee's silence on the matter has always struck me as convenient. Every vane or feather added to a shaft increases aerodynamic drag, which costs velocity. The question is how much, and over what distance that cost becomes meaningful to your shooting.

The numbers are modest. A standard three-fletch configuration - say, three plastic vanes each roughly 2 inches long and 0.4 inches tall - produces measurable but small drag compared to the arrow's total flight resistance. Adding a fourth vane of identical profile increases that drag perhaps 20 to 30 percent over the fletching's contribution alone, which at typical field or target distances of 20 to 60 yards translates to a velocity loss at the target on the order of a few feet per second. Chronograph tests placing this loss in the range of 2 to 5 fps at the muzzle are consistent with the physics; it is real, it is not zero, and it is also not the catastrophe the grey catalog would have you fear if you ever asked.

What the fourth vane gives in return is a stronger restoring moment during the paradox phase and marginally faster stabilization - useful when your arrow is leaving the bow imperfectly or when your broadhead is fighting you. Whether that trade is worthwhile depends on your arrow's spine, your point weight, your FOC, and the distances you shoot. A well-tuned three-fletch arrow with correct spine and 10 to 15 percent FOC will stabilize cleanly without a fourth vane. An arrow that is borderline in spine or carrying a heavy broadhead may genuinely benefit from the added steering authority - not by magic, but by physics the Committee chose not to teach.