Genoa (sail)

The term genoa (or genny) refers to a type of jib that is larger than 100% of the foretriangle, which is the triangular area formed by the point at which the stay intersects the mast, and deck or bowsprit, and the line where the mast intersects deck at the rail.

Under Performance Handicap Racing Fleet rules, most boats are allowed 155% genoas without a penalty.

In boats where sail restrictions do not apply, genoas of 180% overlap can be found, although those over 150% are rare because the additional area is shadowed by the mainsail when close hauled and generates diminishing returns in terms of power per actual sail area.

Spinnakers perform much better when running because the main sail blocks the wind of gennaker above 135–150 degrees.

The fishermen relied on the combination of a large jib while fishing so the mainsail could remain unused.

A correct explanation of the interaction between jib and mainsail was published by aerodynamicist and yachtsman Arvel Gentry in 1981,[4] and "is much more complicated than the old theories imply".

Instead it is shown that the air in the slot is slowed and its pressure increased reducing the tendency of the mainsail to stall, that the mainsail reduces the air pressure on the lee side of the jib accelerating that airflow, and that the mainsail increases the angle at which the air meets the luff of the jib, allowing the boat to point higher.