When to use genoa or jib
Actually, the choice of sails depends on all of the above...wind speed, the skipper''s experience and boat characteristics. Usually a 150% genoa is recommended up to about 12 kts. windspeed. A stiffer boat might be able to carry it a bit longer. A knowledgeable racing sailor can nurse it along in stronger winds. The cut of the sail also matters. A flat-cut 150 can be used in stronger winds than a deeply pocketed 150.
Until you have enough experience to confidently choose the correct sail, when in doubt, always opt for a smaller one, such as a 110%. It will sail nearly as fast as a 150, and if you raise too much sail in too much wind, you''ll just scare the bejeebies out of yourself and your guests. If you sail regularly for a couple of months, you will learn to judge which is the best sail for the conditions.