Storm trysail

Hoisted on the main halyard — ideally in its own dedicated mast track so it can go up with the mainsail still lashed to the boom, a widely recommended practice though not an OSR mandate. Boats with in-mast furling mains must be able to set the trysail with the main furled. The sheets lead to strong points on deck or the quarters — never to the boom.

Under OSR 4.27 the area may not exceed 17.5% × P × E — a formula on the mainsail hoist (P) times the mainsail foot length (E), not a percentage of mainsail area. Since a triangular main is about 0.5 × P × E, the trysail works out to roughly a third of the main's nominal triangle at most. No headboard and no battens; aramid and carbon are prohibited; the sail number must appear on both sides as large as practicable; and the post-2013 high-visibility color requirement applies here too.

The OSR requires trysail sheeting positions independent of the boom: with the boom lashed down and out of the equation, a failed gooseneck or vang cannot take your storm canvas with it, and the boom cannot sweep the cockpit in a knockdown. Designed for propulsion and steerage in Beaufort force 8 on all points of sail. Rig it once in calm weather to learn the sheet leads — a gale is no place to work it out.