Mast aft rig

A mast aft rig is a sailboat sail-plan that uses a single mast set in the aft half of the hull to support a jib or multiple staysails, with either a small or completely absent mainsail. Mast aft rigs are uncommon, but are found on a few production sailboats.

Comparison to other single mast rigs

The small mainsail and common use of multiple staysails commonly found on the mast aft rig resemble some cutter rigs. A cutter is a single masted vessel, differentiated from a sloop either by the number of staysails, with a sloop having one and a cutter more than one, or by the position of the mast, with a cutter's mast being located between 50% and 70% of the way from the aft to the front of the sailplan, and a sloop's mast being located forward of the 70% mark. A mast aft rig could, based on headsail count, be considered a variation of the sloop or cutter, or, based on mast position, a unique rig.

Advantages of the mast aft rig

In the typical Bermuda rig, the jib generally delivers a significant percentage of the driving force. The stay that supports the leading edge of the sail causes far less turbulence than a typical mast, resulting in better airflow across the lee side of the sail. Many Bermuda rigs have slowly grown larger and larger jibs or genoas, and smaller and smaller mainsails, in order to take advantage of the greater lift afforded by the jib. The cutter, with its use of multiple foresails, achieves the same goal of placing a higher percentage of the sail area in staysails.

The ultimate expression of the mast aft rig goes one step further and eliminates the issue of turbulence from the mast interfering with the mainsail by eliminating the mainsail altogether. Additional advantages of using staysails is that they may be rigged for roller furling, allowing the sail(s) to quickly and easily be reefed by simply rolling the sails around the stays. It is this ease of reefing that is one of the main attractions of the mast aft rig.

Disadvantages of the mast aft rig

Mast aft rigs are viewed as unconventional, and since recreational sailors often choose boats based on what "looks" right, mast aft rigs face resistance in the recreational market. Racing sailors will use whatever is fastest within class rules, and class rules are generally very closely tied to the conventional Bermuda rig.

Another disadvantage of the mast aft rig, when set up with no mainsail, is the drag on the mast. While the mast may interfere with the airflow around the mainsail, the mainsail also serves to reduce the drag on the mast. By not having a sail attached to the trailing edge of the mast, the mast becomes a significant source of drag.

Commercial examples

The only successful mast-aft designs were designed and built by Prout Catamarans, Ltd. The Snowgoose models were offered with a mast-aft rig, and it boasted a number of features that made short-handed sailing easier than with a standard Bermuda rig. Broadblue Catamarans Ltd. now owns and makes two of the Prout designs, which still come standard with the mast-aft rig.

Unsuccessful commercial examples include the Delta 26 by Gary Hoyt and the CS-24 by Phil Bolger. Prototypes of both designs were constructed, but neither entered commercial production. Ted Brewer's So-Du-It, designed for amateur home construction, had at least two examples constructed, but the anticipated offshore racing class never materialized.

External links

1. Boats featuring an innovative "wishbone" mast, in both tall and short versions. Another photo of the tall rig. These may or may not have been constructed for the Proycyon project.
2. Revisiting a mast-aft sailing rig
3. Sail power calculator