Fractional rig

Fractional rigs were introduced on race boats in order to allow more controllability of the surface of the mainsail and also less drag when sailing upwind.

[1] Fractional rigs tend to have a larger mainsail and a smaller headsail which is often a non-overlapping jib.

Since jibs need considerable forestay tension to set properly and the amount of tension needed increases with wind speed, being able to drop the jib altogether in windy conditions puts less strain on the rig and hull.

As sailcloth improved in the second half of the 20th century, it became possible to construct sails of a higher aspect ratio.

A fractional rig allows the mast to bend more easily, which in turn allows more adjustment to the shape of the mainsail, especially when sailing upwind.

Under certain conditions, the moment arm that results from these offset attachment points can be used to advantage as this is an effective method of inducing bend in the mast which in turn flattens the mainsail.

If the distance between the attachment points is too great, a mast of average stiffness will be unable to apply optimum forestay tension, unless one of the following mast-stiffening design features is used: