Jake answered it partly right :

here the specs of each boat to show you the differences ;

A-cat
Weight 75 kg = 165,5 lbs
Length = 5.49 mtr = 18 foot
Width = 2.30 mtr = 7 ft 7 inches
Mainsail = 13.86 sq.mtr. (150 sq. ft.) including the mast on a (on average) 9 mtr mast (29' 7")
No jib
No spinnaker
Typically carbon beams and mast and all kinds of other HT stuff
Rating Texel = 99 (F18 is 102)
Strongpoint : upwind work in 3-14 knots


F16 (singlehanded)
Weight 104 kg = 229.5 lbs
Length = 5.00 mtr = 16 foot 5 inches
Width = 2.50 mtr = 8 ft 2 inches
Mainsail = 14.85 sq.mtr. including the mast on a 8.5 mtr mast = 161 sq. ft on 28 ft mast
Jib sail (only in doublehanded mode) = 3.65 sq. mtr. by 5.5 mtr luff = 39 sq.ft. on 18 ft luff
Spinnaker = 17.5 sq. mtr. = 188 sq.ft.
Typically less HT gear. mostly stuff that does the trick for an acceptable price
Rating Texel = 102 (F18 is 102)
Strongpoint : Downwind work under spinnaker and upwind work in 10-20 knots (Applies to both doublehanded and singlehanded setups.


Wouter