Size will depend on whether the sail is hank-on or roller furling
and, if roller furling
, how far off the deck
the RF drum is. Max hoist on my headstay with ProFurl furler
with long tangs to the headstay chain plate
is 38'6". Foot length will be around 18'6".
If you are going to have a sail made, most sailmakers will have the dimensions and only need to know how your boat differs from the standard hank on boat. I've gotten sails
cut for other boats, most notably a 140% RF Genoa
for a Tartan 34C, that fit perfectly.