Fractional Rig

A fractional rig on a sailing vessel consists of a foresail, such as a jib or genoa sail, that does not reach all the way to the top of the mast.

In the picture to the right, the forestay that secures the mast at the front of the boat is attached to the mast at a lower point and the fore sail (jib or genoa) is rigged to this stay. The mast is farther forward on the boat than on a masthead rig and so it has a larger main sail. Masthead rigs are most common on larger keel boats or cruisers.

A fractional rig is typically used on dinghy sailing boats and racing oriented keel boats, such as the J/24.

Fractional rigs were introduced on race boats in order to allow more controllability of the surface of the main sail and also less drag during tacking. According to one manufacturer, "a key to making fast boats easier to sail than slow boats is the fractional rig".

Usually a fractional rig features a larger main sail and a smaller non-overlapping jib. This configuration is optimized for up-wind sailing efficiency. For downwind sailing, a larger jib is more desirable but in the case of many high-performance fractional rig sailboats, the smaller jib is substituted by a spinnaker or gennaker. On many modern skiffs and race dinghies, the jib is relatively small compared to the size of the main and it is normally left in place when the spinnaker or gennaker is used due to this type of jib's minimal aerodynamic interference.

A major advantage of the fractional rig, especially the '3/4' rig (where the fore stay goes 3/4 the way up the mast), is that the jib can be taken in without the boat rounding up into the wind like a weather vane. With the masthead sloop, both the main and the jib must be reefed, when shortening sail, to keep this from happening.

Since jibs need considerable fore stay tension to set properly and the amount of tension needed increases with wind speed, being able to drop the jib first in windy conditions puts less strain on the rig and hull. Fractional rigs are used on lightly built multi-hulls for this reason.