Wouter

yr statement about mainsails' weight is absolutely INCORRECT.

At 8 kg with battens yr main is VERY heavy. You can save easily 2-2,5 kg on it!
In order to prove my assumption I provide you with some figures (as you know 16HP mains are smaller than 18HT mains, but bigger than A class):

A class mainsails weight (with battens) between 2,0 Kg (Extra-Light Oxosails) to 4,5 kg, the average being between 3,0 and 3,5 Kg

18HT mainsails weight between 4,5 Kg (Ullman Cuben Fiber/RBS carbon battens) to 6,5 Kg (BIMARE Pentex /Fiberfoam battens).