You can use" Disolvit" from Bunnings ,its citrus based,comes in a spray pump bottle and works really well to get the sticky residue off monofilm without any damage 
Shellite (NOT white spirit) does a fine job too, without harming the monofilm in any way.
Thank you all. I now remember using desolv-it many years ago. Thanks for the memory jog. I'll go down to Bunnings to see if they have any.
Got the Desolv-it from Bunnings on Friday. Worked like a charm. It turns out that it wasn't sail number adhesive but adhesive from a sponsor sign of some sort.
