As mentioned before, the luff curve of a Tiger main may not match that of a Nacra mast, however if you realy want to, a sail maker can change this. This does not mean the luff curve of a factory Nacra main will be right for your crew weight as well. Sails are very personal and should me matched up with your mast bend properties, crew weight and race conditions (wind, waves).

As for the jib, if the luff length is close, it will be OK. Jibs have a fair bit of adjustment on the clew boards as sheeting angles change with mast rake.

As for kites, luff length is less important as you can always adjust your pole hight or halyard hight. Sheeting angle is the most important part. Most F18s have a fixed sheeting point which I am not a fan off as mast rake will also effect sheeting angle for kites. If you get a kite that has a different length foot, it will throw out your sheeting angle also.

As for sail makers, most of the reputable sail makers (if you choose not to go factory) know what they need to do ie shape and sheeting angles for the major F18 types and can also make personal changes to them to suit your weight / race conditions. For spinnaker shapes, the size of the fleet also comes into play. For small fleets, you want a kite with plenty of grunt for max VMG, whilst large fleet racing you will want a flatter kite for gaining hight if you need to attack or defend on the downwind. Some good aftermarket sail makes include Pablo from Ullman ITA, and Langy. Norths Brisbane, Australia also make some good kites but still working on their working sails. Gran Segel make great Tornado spinnakers, but don’t know if they have been successful with F18s.