There are several aspects that make a fractional rig
make more sense for cruising than a masthead rig
. Because of the geometry of a fractional rig
, where the forestay comes in below the masthead, it is very easy to control precisely mastbend with the backstay adjuster. On a fractional rigged boat, increasing backstay tension stretches the forestay and so flattens the jib
and opens its leech, while mast bent flattens the mainsail and opens its leech. In effect, on control depowers both sails at once. Because of the ability to quickly and precisely depower, individual sails are adaptable to winder wind range and there is less reefing and sail changes required. For similar reasons a fractional rig
can carry a proportionately larger mainsail and more sail area in its standing rig
. Because a fractional rig
can carry more sail area through a wider wind range in its standing rig
, it can get by with smaller and few headsails. These smaller headsails represent a smaller portion of the overall sail plan and are much easier to tack and handle. Since most boats develop weather helm as the wind picks up a fractional rigged boat will often balance with its working jib and single reef which moves the center of effort forward and therefore reduces weather helm. For that matter the center of effort of a fractionally rigged boat is further forward allowing reasonably balanced sailing with only the mainsail.
The reason that simply using a smaller jib on a masthead rig does not work is that since masthead rigged boats do not have the ability to carry sails through as wide a wind range they are usually designed with smaller standing sailplans. Therefore most masthead rigs are designed around using a genoa for light to moderate conditions. With a smaller jib on a masthead boat generally means that you lose the lower end of the windspeed range because do not have sufficient sail area for the conditions. By the same token, because masthead rig boats are usually designed to balance with a genoa, using a small jib with a full mainsail generally results in a boat that has more weather helm than is ideal. (The same problem happens in cutters when they sail under just the staysail).