The radial FR-4 is designed to suit the Seldon Epsilon mast and Superspar M2 masts, it is for crew weights of over 175kgs. The sail is made with a full radial construction and produces a very smooth and easy to use sail and copes better with the high loads in the corners than a traditional cross cut sail allowing the sail to maintain its racing shape for longer. It is manufactured from Contender RSQ 4.55. The FR-4 is derived from the FR3 with a little extra fullness in the foot seaming and lower luff round, it needs a little more pre-bend in the mast to accommodate the fullness and offers a good range of ‘gears’ across the wind range.