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What's the Ideal Sailing Rig...?
Kasten Marine Design, Inc.
Copyright 2001 - 2005 Michael Kasten
Updated 15 April 2005
Rig Choice
Cat, Sloop; Cutter; Ketch; Schooner... these are the basic configurations.
How shall we choose among them?
The type of rig is often a pre-ordained choice once one has determined vessel size, the preferred layout, and the maximum size of sail one can handle. While this may seem somewhat heretical at first, there is no arguing the fact that no one wants a mast in the middle of their double berth...! Therefore, if a double berth right forward is a priority, it is likely to rule out the
schooner rig on a vessel under around 50 feet. For that layout, we would instead tend toward the ketch or cutter rig. On a fairly small vessel though, we might make excellent use of the Cat rig.
How shall we choose?
It is always a benefit to windward performance to limit the number of sails. A cutter will perform better for example than a ketch. Why would we consider a split rig then?
In nearly all cases this choice boils down to the simple question, "What is the maximum size sail you are comfortable handling?" In answering this question honestly, we nearly always discover that on all but the smallest of boats, for general cruising we will probably be better off with a split rig, such as a ketch or schooner. This will serve to limit the size of the main sail for
easier sail handling, and still allow a generous overall sail area. It will also give us the benefit of having a rig that is less tall, so better able to be supported.
Rather than having a preference for any one rig type, I believe this question will best be answered during the course of developing a design. The rig should naturally be suited to the specific purpose for which the vessel is being developed. The following is intended to shed some light on these questions...
What About Windward Performance?
If the keel is very long and shoal, and the rig is similarly low and spread out with gaffs and bowsprits and multiple masts (like a mid-1800's US coastal fishing schooner) then it is likely that performance will be excellent when reaching or running, but far less than optimum to windward.
At the opposite extreme (disregarding hull form for now) is a deep narrow fin keel, with a tall high-aspect Marconi sloop rig. This type of vessel will ordinarily scream to windward, but will be very much the inferior type on other points of sailing, thus the requirement for spinnakers and a plethora of other reaching and running sails.
Of course these are two extremes - and we need not fall into this kind of extremist thinking for the discussion at hand. Given all that we have learned about windward sailing since the days of old, there is absolutely no reason that there should be poor windward performance on any vessel, nor poor off the wind performance necessitating a large sail inventory (read expense and hassle). There is
certainly a wide middle ground here...!
For example, a modern NACA foil keel and modest aspect rig will serve extremely well for all around sailing. Take for example the rig on the cutter design Fantom, a 'Bermuda' rigged cutter.
If it is desired to not have a bowsprit, then in order to achieve adequate sail area, the rig will simply become taller, and the keel deeper. If it is desired to further enhance windward sailing, then modifications are made to the keel, etc, eventually tending toward a separate keel and skeg-rudder configuration. An excellent example of this is the preliminary
design of the 50' ketch Sonja.
Quantifying Performance
The type of rig one chooses will certainly have an effect on performance, as will the amount of sail area. For maximum performance, there is much benefit to be had with a good hull and keel design, and with well proportioned and well cut sails. We tend to observe many older vessel types which may have neither optimum hull design nor well proportioned sails, and pass
judgment on the type. Instead, we should look at the components of good cruising performance, and optimize the hull and sails to suit those highly specialized requirements.
Aspect Ratio is defined as the height of the sail squared, divided by the area of the sail. A perfectly square sail would have an A/R of 1. A 450 sq. ft. triangular sail with an A/R of 6 would have a 52' luff and a 17' boom. They are both extremes.
It is well known that higher aspect sails produce greater lift when close hauled. It not so widely known however that high aspect sails stall much more readily as the angle of attack widens. As A/R gets higher, sails get less and less efficient at pulling when anywhere but close hauled.
For racing, where windward performance is of prime importance, it has been shown that an aspect ratio greater than 6 is of little use on monohull racing craft. An appropriate range will be an A/R of from 4 to 6.
A polar diagram showing lift vs. drag plotted for sails having the same area but differing aspect ratios very graphically shows that the favored lift / drag position is quickly handed off to shorter and shorter rigs as a sail is eased. If you would like see this data graphically presented, please have a look at the Aero-hydrodynamics of Sailing by Marchaj, p. 444, Fig. 2.138.
A study of this data shows that the most favorable aspect ratios for ocean cruising, where all-around performance is the goal, an aspect ratio from 2.5 to 3.5 is very appropriate, with an approximate upper limit of around A/R 4. Naturally, these are not "hard" boundaries, only guidelines. In most cases, a compromise is struck in consideration of the times inevitably spent sailing
to windward.
In the data presented by Marchaj, angle of incidence of the sail is plotted against lift vs drag. A sail having an A/R of 6 performs exceedingly well at an angle of attack to the apparent wind of 10 degrees, where lift divided by drag (L/D) yields a ratio of around 8.5. At 10 degrees, a sail with A/R 3 has an L/D ratio of 6.5. At 15 degrees, the A/R 6 sail has an L/D ratio of
4.47, and the A/R 3 sail has an L/D ratio of 4.5. At 20 degrees, the A/R 6 sail has an L/D ratio of 2.7, while the A/R 3 sail has an L/D ratio of 3.3, and so forth. By the time an angle of attack of 30 degrees is reached, the favored position is handed off to a sail with an A/R of 1...!
The salient point is that extremely high aspect sails are not "bad" sails, they are just not a requirement for general ocean cruising, where it is rare to be sailing dead to windward. When required to do so, sails with an A/R of from 3 to 4 will perform quite well when just eased off a few degrees.
The benefits of lower aspect sail rigs become more evident when performing the engineering stunts required to keep an A/R 6 rig from collapse. The simpler rigging made possible by lower aspect sails will be its own reward in terms of ease of construction, and in terms of rig stresses. This usually translates into longevity of the rigging components, generally considered the holy
grail for cruisers... the maintenance factor.
Whether using a Bermuda rig, a "Marconi" rig, or a Gaff rig, these factors generally encourage keeping aspect ratio under around 3.5 to 4 for an ocean cruising vessel. To see an example of this type of Bermuda rig, please check out the Fantom.
Rig choice is mainly a matter of assessing one's priorities. If they tend toward racing, then the choices will be quite different than those of the cruising sailor.
Keel Profile
If the rig is very tall, the lever arm is relatively longer from the center of lateral resistance to the center of effort of the sails, so the keel must be proportionately deeper to compensate. If on the other hand, the rig is kept fairly low, there can be much less draft, and still be very adequate sail carrying ability.
For the best steering and course keeping behavior, and for the greatest overall structural strength, a long full keel offers the most benefit to the long distance cruising sailor. This type of long and relatively shoal draft keel is ideally suited to the lower aspect sail rigs, say up to an aspect ratio of around 3.5.
A good example of this thinking is provided in my design Redpath, having relatively shoal draft and generous sail area, yet good sail carrying ability. Other examples with similar qualities are my Benrogin, Lucille, Grace, and Shiraz designs.
For the ketch Shiraz, the rig height was limited to 60' off the water for convenience while traveling the ICW along the East Coast, and the draft was limited to 5' - 6" for sailing in the Bahamas. Since Shiraz is an aluminum vessel, there is actually greater sail carrying ability than necessary, so we have the option to give her more sail area, or we may on the other hand choose to keep
the rig as-is and assume there will be an extra margin of safety when flying a mule and a spinnaker... Without the rig height and the draft restriction, Shiraz could for example be given a higher aspect rig, possibly using a Bermuda mains'l.
Taking the Shiraz example a bit further, if increasing the aspect ratio of the mains'l, a deeper keel would be desirable. It might be preferred at that point to consider splitting the keel into a deeper portion to contain the ballast, then a shallow portion to contain the shaft alley, then another deeper portion to act as a skeg for the rudder. This would allow a very efficient
foil shaped "cruising fin" type of keel, and a similarly efficient combination skeg / rudder combination, while also limiting wetted surface.
When the aspect ratio of the sails becomes greater than around 3.5, the split keel configuration with a long "cruising fin" and skeg hung rudder will usually be preferred. Primarily this choice will be made in order to deepen the keel (and the ballast) but to avoid extra wetted surface. For quick maneuvering, this kind of keel will always be a bit more responsive. The
"cruising fin" keel, having a higher aspect ratio and therefore greater lift vs. drag, will naturally have better windward performance than a long and relatively shoal full keel. If not carried to extremes, this will not materially degrade course keeping ability.
Of course when the rig becomes very tall, the keel will become proportionately deeper. Windward performance will be improved, but performance on other points of sail will be degraded, as will course keeping ability. Taken to its logical extreme with deep fin keel and spade rudder, when running in a sea of any size attention to the helm will be critical. This is especially so
with fast high aspect sea-going sleds having very fine entries and broad flat sections aft, where lack of attention to the helm may result in an instant broach. While there is no question that this is exhilarating sailing, it can hardly be recommended for safe family cruising...
For long passages with the helm relatively unattended, a long and relatively shoal full keel will always be more steady than any other type. For long distance cruising, a longer keel will "track" somewhat more like it is on rails. In harbor, maneuvering turns will have a large radius. The tactic in that situation is to use a bit of reverse gear to take headway off the boat, then
give it a burst in forward gear with the helm over, then another burst in reverse, etc. With that, any full keel boat can be pivoted in her own length.
Rather than there being any right or wrong choice, the type if keel profile is a matter of preference, usually based on the type of sailing that is planned. During the design process, once the preferred keel configuration and the preferred rig type are chosen, it is simply a matter of balancing them against each other in order to obtain the required lead for the sail area vs the lateral
area, and to place the ballast where required for proper trim.
Regardless of whether a design is given a long full keel or a "cruising fin" keel, it will benefit performance both on and off the wind to make use of an efficient NACA foil shape. The particular choice of foil type will depend on the keel profile in order to maximize lift, and minimize drag.
What About Winged Keels...?
Should the cruising sailor consider a winged keel...? An excellent question.
The wing keel concept is not brand new. It has come to us as an evolution of various approaches from the past.
For long full-keel applications, the idea was promoted to some extent by Henry Scheel from the 1960's onward. It became known as the "Scheel Keel" which has the form of a modified "bulb" along the base of the keel. The particular configuration is to widen the base of the keel via a broadly curved keel bottom (athwartships), with a concave return to the body of the
keel above. This creates both a large envelope for the ballast down low, without having to increase draft, and also effectively provides an "end plate" to reduce the induced drag from eddy making at the base of the keel foil.
Among racers, this concept is transformed into a blade with a distinct "bulb" at the base containing the ballast. This serves the same function as the Scheel type of arrangement, i.e. to lower the ballast and to reduce eddy making at the tip of the keel. A few bulb keel examples can be seen on the 96' schooner Zebulun and the 50' ketch
Sonja.
The further evolution of the simple bulb is a "bulb with wings." Quite a few combinations have been developed, including several that are aimed more at the cruiser / racer types.
In moulded fiberglass or cast lead, nearly any shape can be achieved. In metal construction however, one of the basic challenges in order to keep building costs within bounds is to make use of shapes that are both easily fabricated, and that are also efficient in use. For a cruising boat, an additional priority is to create a structure that is sufficiently robust to withstand
serious abuse.
In metal construction, for the greatest economy of labor during fabrication (i.e. the most bang for the buck) the most reasonable approach is to make use of simple and distinct shapes, rather than "blended" surfaces as would be more typical with fiberglass construction. For metal construction therefore, if a bulb is planned, it will ideally be a distinctly formed shape, attached to
another distinctly formed shape, the keel foil. If wings are provided on the ballast bulb, they will also ideally be distinct "appendages" having a long low aspect shape. If a Scheel type of keel bottom is planned, then for ease of construction it will ideally make use of large diameter heavy wall tubing for the bottom shape, and sections of similar tubing for the concave "return" to the keel foil.
The cruising sailor empirically observes, "What sticks out, breaks off." To address that observation, appendages to the hull are approached with an extreme conservatism... With a winged keel, we have added an appendage to an appendage...!
I believe an approach such as that taken by Scheel, or possibly a bulb or modest bulb / wing arrangement, will have the greatest merit for the long distance cruiser. The primary requirement is that the boat be able to take the ground and heel right over on the hard without any chance of structural damage, for which the plain keel, the Scheel arrangement or the bulb keel are
ideally suited.
Is the Gaff Rig Suited to Modern Cruising...?
If windward sailing is of paramount importance then of course the Bermuda rig has much to recommend it.
For modern day cruising the gaff rig is often maligned. In my view, for blue water voyaging the gaff rig has much to offer.
If a vessel's keel is shaped efficiently and if the sails are cut for maximum efficiency on the wind and if the sail plan has been designed well, a gaff rigged boat will perform incredibly well, in many cases besting the performance of a high aspect ratio Marconi rigged boat. This is especially so if one is sailing on any course other than a hard beat to windward.
A gaff rig provides the chance to set more sail area on a given length of mast. For a given sail area the mast can be quite a bit shorter, so the mast will be that much stronger and will require less complex rigging to keep it in place.
The stiffness of a column is inversely proportional to the square of its length. A mast that is twice as long will fail with only one fourth the load, therefore must be four times stronger. One strategy is to use a heavier mast section. The more typical approach is to divide the mast into several "panels" by the use of spreaders. This is the "Marconi" rig. It
introduces more stress, more places for failure, more cost, more maintenance, etc. For racing, this is of course justified.
For general cruising however, we can make a good case for keeping things simple and strong. If set up simply, a traditional rig will be friendly and easy to use. For example, one will be handling soft lines rather than harsh stainless wire and winches. If the sails are laced, we will have eliminated sail track and other hardware, along with its relatively much greater expense.
This is not to say that one should be old fashioned... far from it!
For example, nearly all the masts I specify are welded aluminum tube or pipe. These are perfect for the gaff rig as well as for the low aspect Bermuda rig. Compared strictly on a strength to weight to cost basis, aluminum pipe spars are impossible to improve upon.
As further example, among the gaff rigs that I have drawn, one will observe that I prefer short gaffs without tops'ls. Primarily, this is for reasons of simplicity, efficiency, and ease of use. The penalty in excess rigging required for gaff tops'ls is more than I'm usually willing to fool with while sailing. In my
experience, due to that added complexity, gaff tops'ls often just sit in their bags unused. In exchange for the added complexity of rigging, gaff tops'ls ordinarily provide little gain in terms of usable sail area.
Notes on the Short-Gaff Rig
My short-gaff sail plans are meant to address the shortcomings of the traditional types of gaff rig sail plan. By using a short gaff with no tops'l, there is more luff length to the sail. This arrangement permits a single halyard on the gaff, using a fixed bridle that is balanced during sailing trials, then permanently made fast at the best spot. With a longer luff on the
lowers, the lower sails are able to perform much better when on the wind. As an added bonus, sails are not broken into such small units, so are able to be more efficient on all points of sail. In fact, in its ideal form the short-gaff-sail is fairly close in profile to the shape of the fully battened elliptical plan form racing sails of today.
The short gaff strategy is not my invention by any means... It was developed and was well proven on vessels such as the Dutch sloops, Bermuda sloops, and of course the pilot schooners of the last century that sailed out of Baltimore. The pilot schooners needed a foolproof rig that had superior performance, and that could be handled by a man and a boy. They were large
vessels...! Applying the same strategy to smaller sailing vessels, one can very easily single hand a 50 footer. As far as the sailing properties, they are well documented among those vessels, and by my own experience having sailed with them.
What About the Schooner Rig?
The schooner is able to spread more sail per length of spars than any other rig. This allows a generous sail area, while the center of effort is kept low down.
On a schooner of any size I like to arrange for both main and fore sails to be similarly sized. This is done to prevent the mains'l from becoming too big to handle. To determine the size of each sail, one should try to make use of sails as large as can be confidently handled, and no larger.
Much of what is written about schooners and gaff rigs assumes that one will be using a traditional sail plan with long gaffs, two halyards for each gaff, main and fore tops'ls, fisherman tops'l, stays'l, jib, jib tops'l, etc. Added together even on a small schooner, that represents some twenty halyards and other control lines.
As an example of how one might simplify that configuration, Lucille and her sisters, Redpath and Benrogin have only four halyards for the lowers, and two for the fisherman tops'l. The total: six halyards... ! Simple is beautiful...
Redpath as Example
We had the opportunity to sail two 34' schooners having exactly the same hull form and sail area against each other. One vessel had a "traditional" gaff schooner rig, with long gaffs, gaff tops'ls, stays'l and flying jib. The other vessel had a short-gaff rig of my design with exactly the same sail area. One feature of the rig I tend to prefer (as with designs like
Redpath) is that the working sails are sized to be as nearly alike in area as possible, so there is no single dominant sail. All of these improvements served to simplify and lighten the rig and provided far less windage.
The result...? Although both vessels performed more or less equally on a down wind course, we out sailed the "traditional" rig hands down both reaching and beating. This combination offered much better windward performance with a simpler rig that is still what we would refer to as "classic."
Another bonus is that the simper short-gaff rig was far easier to build, to handle and to maintain. I liked it so much that I made an identical rig for my own schooner,
Emerald.
Redpath was yet another refinement of the concept, having been designed to take best advantage of the optimum rig right from the beginning. Taking Redpath and other similar designs as examples, the improvement in windward sailing performance is significant. The combination of the NACA foil keel and the taller and more efficient
short-gaff rig provides between 5 and 10 degrees closer sailing tack to tack (the "real" measure of performance) than does a more traditional schooner type having tops'ls, multiple jibs, a nest of extra halyards, and a long straight shoal draft keel.
Redpath is relatively light in terms of displacement to length, and has a high sail area to displacement ratio in her working sails. This not only makes the boat fast, but also makes the rig ultimately easier to deal with, since there are no light weather spinnakers and so forth to fool with. For light weather sailing, the Fisherman Tops'l is kept very well controlled between the
two masts, having a line at each corner.
If one could say there is any single factor responsible for providing excellent performance on Redpath, it would have to be attributed to the amount of sail area provided. The sail area given to Redpath is able to be generous because it is located relatively low down, rather than on one single tall stick. A
Marconi type of rig will ordinarily require a deeper keel for adequate sail
carrying ability.
One cannot make reasonable comparisons of course to vessels having a fin keel, spade or skeg hung rudder, and sloop rig, as those types will always have superior windward performance. What those keel and rig types give up in terms of off-wind sailing is considerable... Steering stability off-wind is compromised, as is safety in taking the ground, as is the ability to heave to
gracefully, etc.
The main thing is simply to define the type of sailing one wishes to do. If it is "round the buoy" racing, then shoal draft and low aspect rigs will not be competitive and thus they will be very unsuitable. Nor are they intended to be suited to that type of sailing... It is the windward leg after all that inevitably wins a round the buoys race.
For offshore voyaging, relatively more shoal draft and lower aspect rigs will ordinarily make the most sense. Redpath, for example, is designed for fast sailing. On any course from a close reach to a dead run, using only her working sail (not allowing the Fisherman, spinnakers, or any other light weather sails), Redpath simply will walk away from the majority of equally sized Marconi rigged boats.
For offshore voyaging one would be hard pressed to do better... Particularly if ruggedness, ease of handling, economy and ease of maintenance are of any import.
The Schooner Lucille
Image, Copyright 1999 Lena Kasten
Other Useful Cruising Sails
For Schooners: The Fisherman Tops'l
On a schooner, the fisherman tops'l is an excellent tool, is easy to use, and provides plenty of area, so is well worth it. The fisherman tops'l is a thing of beauty and highly functional, without a lot of complicated rigging. It's like having overdrive... It's up where it can catch the breeze and it has a meaningful size, so that the reward for setting the fisherman is substantial. Of
course, a Fisherman tops'l is not absolutely required, but it is almost silly to do without one on a schooner, given the outstanding opportunity between the masts to spread a large amount of sail without much fuss or bother.
For all Sailing Vessels: The Stays'l or "Mule"
One might be tempted toward even greater simplicity, eliminating the staysail and outer jib in favor of a single jumbo jib. We can quickly see however that a staysail and jib combination are a bit better suited to offshore sailing, as follows:
The most obvious advantage of the stays'l, whether it is on a schooner, ketch or cutter, is to make the individual headsails smaller and easier to handle. A much less apparent advantage is that the stays'l also provides for easy self-steering. A "steering sheet" led from the stays'l boom, aft along the windward side, and then to a tiller will give reliable and easy self steering.
It's hard to believe, but this really does work...!!
The gaff rig being somewhat lower aspect, lends good self steering to the boat particularly when sailing long passages off the wind. Naturally this statement must be qualified by presuming that the rig is of good design, and that a good hull form for self steering has been provided. You can see example vessels of this type by clicking on the links to the schooners,
Lucille and Redpath , and the very fine ketches Grace and Shiraz.
For Nearly any Hull Type: The Junk Rig...
Along with the Gaff Rig, the Chinese Junk Rig has much to offer in terms of simplicity, ease of use, and also in terms of safety, in particular for the long range voyager. For more information, please have a look at my web page on the Chinese Junk Rig.
Choices...
All of these choices are just a matter of degree; of one's intended sailing; and ultimately of one's preference. One type is not inherently "wrong" or the other inherently "right" but instead are just differing expressions of one's preferred style. Therefore... there really is no argument with regard to keel and rig choices. In the end, the majority of these varying design factors are simply
a matter of the owner's preferences being expressed in the type of vessel being created.
This is certainly not to say that "style" supersedes function... However it is very much to say, in the sense that the vessel will be one's habitat, that the creation of a certain kind of lifestyle very much *is* its function. That lifestyle implying first that it is affordable, that it be easy to keep, comfortable, safe, friendly, etc. These are the feelings we usually wish to invoke by the
term, "home."
For my own purposes, somehow a Lamborghini Diablo does not invoke this feeling. A Bentley is much closer to the mark...!
We have created designs in all styles which vary from the ultra modern to the old fashioned here.... but... it is the more traditional styles - if given the benefit of modern materials and construction techniques - that often seem the most inspiring, especially in actual use. They are more friendly in aspect, graceful, likeable, easier to build and to maintain, and therefore much less costly to build and to keep than their ultra modern brethren.
That there is an element of maritime heritage being brought forth into the light of day is a particular delight - and even more so if we are able to intelligently select those elements of tradition to leave alone, and those that we can improve upon in a way that is compatible with the type, and in the process end up with a stronger, safer, more comfortable, and even more elegant habitat on the briny sea...
Image Copyright 1999 Lena Kasten
Other Resources...
For further reading on self steering, please see the excellent book, "Self Steering for Sailing Craft," by Dr. John Letcher. For further reading on the gaff rig, please have a look at "Hand, Reef and Steer," by Tom Cunliffe.
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