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Revisiting a Mast-Aft Sailing Rig

by Brian Eiland,
RunningTideYachts, Ltd.

Gamefishing Under Sail.  Copyright 2001 RunningTideYachts, Ltd.  All Rights Reserved.

     Twenty five years ago, I was a younger fellow aspiring to become a sailing yacht designer. I was particularly interested in ocean going, cruising boats. I would devour every reference I could find on what made sailboats work. With keen interest I followed new developments on the racing circuits, believing that this was the incubator of fresh new ideas to speed our progress across the seas. Surely this breeding ground would bring significant evolution to the sport of sailing and the art of designing.

     "Au contraire," I became disillusioned so soon. Bruce King's fantastic twin, asymmetrical, bilgeboard development, disappeared in little over a year. Prof. Jerry Milgram's cat-ketches were afforded a similar welcome.  Truly different sail rig innovations were totally discouraged, and numerous other design innovations were "rated" out of existence by handicap racing rules. Ocean going boats were not being designed to "mother-ocean's rules," but rather to some arbitrary, man-created, racer/cruiser rule.

     No thanks, let me look elsewhere. A group out of England, AYRS, Amateur Yacht Research Society, came to my attention. A relatively new group of multihull enthusiasts and their new publication, "Multihulls Magazine," also caught my attention. Here were some sources of true experimentation, innovation, and creativity; and subsequent evolution of the art of sailing, unbridled by handicap rules. Today, look at the French and their fantastic ocean racing boats both mono- and multi-hull; exciting innovation.

     Evolution; nature's onward march to better itself by slowly rejecting less efficient characteristics of the whole, and either replacing them with more efficient offspring, and/or redefining the whole as an entity. Change comes so sloooow in traditional sailing . Look how long it took the traditionalist to adopt the fully battened mainsail that multihulls have long been exploiting for the better part of 25 years. Did they just resist acknowledging it because it was foreign to them, or was it the handicap rules? I suspect both. But there is no doubt to its superiority; ah evolution!

     Now before you get too comfortable with this full-batten mainsail idea, realize that I do here intend to lay seize upon the sacred mainsail of the Bermudian rig.

     One of the most influential books I had read was "Sailing Theory & Practice" by C.A. Marchaj. He subsequently published another, "Aero-Hydrodyamics of Sailing". Both of these books are the definitive technical source of what makes a sailboat sail. And one other book, "The Art & Science of Sails", by Tom Widden and Michael Levitt, correctly describes the slot-effect between the jib and main sails as explained comprehensively by the aerodynamicist Arvel Gentry. In other words almost all the other sailing books are wrong, and many of today's best sailors can not describe correctly the aerodynamic interaction between the headsail and the mainsail.

     With Marchaj's book as my technical guide, I began a search for alternatives to the traditional Bermuda rig. Fore to aft sails must be retained for their windward ability, and the single-masted rig would be preferred for its simplicity. There are three basic positions for a single-masted sailboat: in the bow ~~ which is a cat boat, in the middle ~~ which is the Bermudian sloop or cutter, or in the stern ~~ which is a ....? As Garry Hoyt noted, "the fact that this stern-placed rig has no official name attests to its almost complete lack of popularity". But maybe placing this aerodynamic hindrance at the rear of the sailplan makes sense? Years ago Victor Tchetchet experimented with it calling it the "mastaft" rig. Garry Hoyt, world renown for his cat rigged Freedom boats, built a rear-masted prototype he called the "Delta 26"*. In 1964, a McCurdy & Rhodes 46' "staysail ketch"* stepped the mast aft to eliminate headsail overlap and permit the genoa to be self-tending. Prout catamarans have made use of mast aft rigs (albeit very conservative, small sail-area rigs*) for years. And finally a "staysail cutter" rig proposed by a maritime artist and historian, Melbourne Smith had a significant impact on my thought processes.

     The real driving force to develop an alternate rig was the many negative characteristics attributable to the mainsail

    a) The Bermudian mainsail operates behind a mast at its leading edge. Mast induced turbulence renders totally ineffective, the first 1' - 2' strip of sail area all way up the luff of the sail. This is a sizable area not doing work for you. Want simply and dramatic proof; go rent a Hobie (or any other) cat and take it for a sail with its mast restrained from rotation. On the same point of sail, let the mast rotate and experience the acceleration as the addition sail area comes into play.

    b) As much as the top 15% of the narrow, triangular head of the mainsail is useless behind the proportionally larger mast profile. Not only is this sail area ineffective, but the aero-configuration induces significant drag. Modern multihulls have been cutting this upper portion of the mast height off, and adding a 'fat headed' mainsail. Even the old 12 Meter "Lionheart" exploited this theme.

    c) Almost universally, clumsy booms and all their associated vangs, mainsheets, travelers, outhauls etc., etc. are utilized. Lots of (excessive) hardware and many occasions for this hardware to interfere with the sailor's bodies themselves.

    d) Conventional booms excessively flatten the foot of the mainsail, and are often oversheeted, contributing significantly to the leeway forces. I once had a copy of a test* on a Morgan 41' Out Island ketch , where upon removing the mainsail, the boat lost only 1/2 knot of speed, but cut its leeway in half (from 11 to 6 degrees). A staysail was then rigged between the masts in place of the mainsail, and the boat regained 1 knot of speed while retaining its decreased leeway.

    e) The draft pocket of the main is inclined to the vertical such that the sail drives forward and downward. On reaches and broad reaches this contributes lots of downward pressure on the hull(s), and particularly the bow(s).

    g) Fully battened mains are definitely much more efficient, but pay a price in additional hardware, and a significant weight penalty. In larger boats these sails are not easily raised by man power. And unless they're attached to a rotating mast, they still suffer a significant loss of effective sail area.

    h) Mainsails do not come down or go up with any ease unless the boat is pointed into the wind. And this shortcoming is exacerbated in heavy weather.

     Considering just those characteristics above, we really do have to call into question the use of a mainsail at all. No wonder the normal design practice when drafting a rig's C.E. (center of effort) evaluates the genoa at twice the effectiveness of the mainsail.

     So what did I come up with? Lets call it a marriage between a cutter and a ketch without the mainsail. The original design was published in Yachting 1974 and in Multihulls 1975. Rudder magazine also made note of it in 1974. It was "A Unique New Cruising Rig," designed to go on a 55' cruising cat I was working on at the time. It didn't get built and neither did the rig. It went into hibernation.

     My description of the rig from 25 years ago (copy avail) still covers most of the basics. I was looking to discard the inefficient mainsail, and replace it with two clean leading-edge headsails (ala cutter), acting in a parallel, harmonious fashion, and with no mast spreader overlap so they might be sheeted in for optimum pointing. This necessitated that the mast be stepped aft in the cockpit area and canted forward approximately 10 degrees. The leading headsail is equivalent to an ordinary masthead genoa. The inner main-staysail will replace the Bermudian mainsail and perform a similar function in a more efficient manner, as its leading edge is not fouled by a mast and its foot not misformed by a boom. The wind slot between the two headsails has been made larger than on a conventional cutter rig, which increases the effectiveness of the mainstaysail itself, and very importantly, the parallel nature of this slot produces a much more favorable interaction between these two sails than the ever-variable, triangular slot between the traditional main & jib. Equally important the draft pockets on these two headsails are both in harmony, lifting and driving ahead as opposed to the old Bermudian mainsail which drove downward on a reach.

     Adding a mizzen sail to one of the backstays turned the boat into a ketch without the addition of another mast and its associated rigging. This increased my total available sail area on this single-masted rig. A ketch rig divides the sail area up into more manageable size sails, and it produces a rig with a lower center of effort (less overturning moment) than a sloop of the same sail area. Peter Spronk accomplished this nicely with his schooner rigged cats (but schooners require two masts). Tweaking the adjustment of the ketch's mizzen sail provides a finite adjustment to the balanced helm of the boat. Literally the boat can be made to sail without a hand touching the wheel.

Profile View.  Copyright 2001 RunningTideYachts, Ltd.  All Rights Reserved.

     Now check out the CE's of the sails on the profile view.  This rig maintains it's balance under a variety of sail combinations. Shorten sail initially by just rolling up the mainstaysail, and continue smartly under the genoa & mizzen combination. Wind really coming up, furl the genoa & mizzen and unfurl the mainstaysail. Not only is the sail area reduced significantly, the height of the CE is lowered substantially and correspondingly the overturning forces; and the rig is still in balance! Storm conditions arriving, zip the heavy-weight storm trysail on over the roller-furled mainstaysail. And all this could be accomplished without ever turning the boat into the wind!!

Consider a couple of other interesting comparisons.

    a) For a conventional sloop to carry the same sail area as our new rig, it would require a mast at least 7' to 10' taller. It's sail area would have to be even larger to match our rig's effective sail area, when you factor in the inefficiency of the sloop's mainsail. This larger sloop rig then contributes more overturning force, as well as more leeway force, as well as more bow burying force.

    b) For identical sail areas, our "single-masted ketch" has an even lower height CE than the traditional two-masted ketch. Plus, the weight of our rig (and particularly the mast) is more favorably centered over the boat's motion center, contributing less to the vessel's pitching motion (Almost like gaining the benefits of a modern carbon mast without having to have one). And our mizzen is not operating in the shadow of it's own mast.

    c) The one condition in which the modern fully-battened main might outperform us would be extremely light air which wouldn't support the hanging weight of the sail cloths in our jibs, and in this light a wind, I'd just soon be under power.

     Gone is the heavy, low slung boom, as is the first aid on bashed heads. Gybing is less dangerous; and without sailtrack, jammed mainsail slides are gone. We can even reef our sail area without having to turn into the wind. All the halyards can be located in the cockpit as well as all the winching.

     And finally the most often asked question about this rig: how do you keep the leaning mast up? Well like any other mast, utilize creative, structural rigging (there are some patent-pending applications here). The only time any other sailboat's mast is standing straight up is at rest, at the dock. Otherwise its always leaning over under sail. There are even numerous vessels which, at rest, had their mast raked back at a greater angle than mine is raked forward.

     Only recently as I began designing my 65' gamefishing cat did I reevaluate the many virtues of this mast-aft rig. Once you hook a big fish you must get rid of all sail immediately, and this must be accomplished on any point of sail (no time to point up into the wind). This rig will do that. And if you're going to try and get a non-sailor to try fishing under sail, this thing better be real simple to operate. All three sails simply roll out and roll up. For fishing the mizzen's wishbone boom simply swings up out of harms way. Some of those virtues in summary:

    1) A cruising rig that is more aerodynamically efficient, which should enable you to get the same speed with less sail area, or more speed with the same sail area.

    2) A rig that delivers a clean leading edge for all the sails

    3) A rig that allows the whole sail plan to be roller-furled away or deployed.

    4) A rig that allows the reefing of the sails without turning into the weather.

    5) A rig that divides up the total sail area into smaller manageable sizes.

    6) A rig that maintains its balance center (CE) with different sail combinations.

    7) A rig that produces less overturning moments.

    8) A rig that can be operated without leaving the cockpit.

     One single person could sail this fairly large rig from anchor up to anchor down. All the sails roller-furl, and the mainstaysail and the mizzen both can self-tack. Only the genoa needs to be tacked over, and this could be delayed until the boat has come about. Even motorsailer folks should appreciate this rig.

     In conclusion I want to note that I am not suggesting that this mast-aft configuration will or should replace the Bermudian rig, but rather that not all boats must have the preordained  Bermudian rig. There are, and should be alternatives. Garry Hoyt's stay-free, cat rigged, wishbone boomed, Freedom boats are a wonderful example of a relatively simple, efficient cruising rig. One should give serious consideration to the fundamentals of the ketch as an offshore cruising boat rig, and with this in mind look at the similarities with my rig. Is not my rig an efficient evolution of the ketch concept?

     Please direct serious inquires to RunningTideYachts, Ltd:

Brian Eiland
RunningTideYachts, Ltd.
8304 Whittier Blvd
Bethesda, MD 20817
(301) 469 8382


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