Where can I find formulas for calculating winch size based on things
such as sail area boat length displacement.

Thanks for any suggestions

Mads

Have you checked the West Marine catalog? Their sailboat rigging
section has some good sizing and load estimation data based on sail
area. If you sail short handed or with undersized crew I'd tend to go
one size larger in most cases. My recollection is that typical jib
sheet loads on a boat in the low to mid 30 foot range were on the order
of about 1,000 lbs.