Free-Standing Mast Designs

Free-Standing Mast Designs2017-01-02T12:38:38+00:00

The free-standing rigs all started by chance

wobegone-daze-1When Arliss and I started our 11,000-mile voyage to California in Duprass, I don’t believe we ever came across an unstayed rigged boat, as they were then known, such as Garry Hoyt’s Freedom designs. That was 1977-78, and Freedom Yachts had been in existence only a few years. Little did I know that I would eventually be designing some of the Freedom Yacht masts.

I soon became acquainted with boat designer and renowned Flamenco guitarist Richard Black who had moved to Ventura, CA, shortly after we settled there. Richard was going to build his first boat design, called the Shearwater 28, in Ventura. It had an unstayed cat ketch rig. Richard hired me to design masts for his boat made from tapered aluminum tubes which was my first attempt at engineering and design for unstayed masts. Ultimately, Richard was able to get carbon fiber masts designed and built by a California supplier. About the time the boat was launched, Arliss and I had moved to Newport, RI, and I was an engineer at Tillotson-Pearson Inc. (TPI), builders of the Freedom Yachts in Warren, RI.

My time with TPI and Freedom Yachts

kriter-lady-iiRight at the time I joined TPI, they were starting to build the Freedom Yacht masts out of carbon fiber on their flagpole/lightpole assembly line instead of building them with tapered aluminum tubes. The chief engineer left the company soon after I joined, so I rose to his position and carried on with all new spar design and engineering. I went onto design the masts for the Freedom 44, Freedom 25, Freedom 39, and the Freedom 21. In addition, I designed the masts for the triple-masted Freedom 70, a contender for the 1981 Whitbread Round the World Race, which sported the largest and strongest unstayed masts in the world built to that date, a record that stood for well over a decade.

On my own again

When I left TPI at the end of 1981, I had to remain silent about TPI’s mast engineering and manufacturing for a year because of a non-disclosure agreement I had to sign. But I had become a devotee of the unstayed rig. There was just one problem — I did not like the term “unstayed,” it sounded too negative. I adopted the term “free-standing” to describe these rigs with no wires holding them up because it sounded a much more positive term. I then decided to establish my credentials in the design and engineering of these rigs by writing the first technical paper on the subject which I presented at the 1983 Chesapeake Sailing Yacht Symposium: Design and Engineering Aspects of Freestanding Masts and Wingmasts. This would be my first official design and engineering statement. But I also wanted to write a lay-person’s version of the topic, and correspondingly convinced SAIL magazine that they just had to have an article about free-standing masts, written by me, of course. SAIL bought the idea, and the article, Engineered to Stand Alone, came out in October 1983.

Relationship with PLP Composite Technologies Inc.

In the spring of 1982, I attended a mini-conference about composites at Roger Williams College in Bristol, RI, where I met Bill Bazley, the owner of Plastic Laminated Products, a fiberglass flagpole and lightpole manufacturing company in Fitzwilliam, NH, later known as PLP Composite Technologies. Bill showed the audience some pole samples he had made in carbon fiber. Shortly thereafter, Bill and I partnered to design and build carbon fiber and Kevlar spinnaker poles for the 1983 America’s Cup in Newport — the one in which the US lost the Cup to Australia for the first time. During the American Defender trials, our wet-lay-up spinnaker poles were on Courageous and Liberty, but the third American boat, Defender, had a much better spinnaker pole made from pre-preg carbon fiber. Courageous, with our pole, beat Defender. So Defender was out and Courageous grabbed Defender’s spinnaker pole and retired ours. Then Liberty, with our pole, beat Courageous, and then similarly grabbed the Defender spinnaker pole to sail against Australia II for the America’s Cup. Well, the rest is history, Dennis Conner and Liberty lost the America’s Cup. I always wonder what would have happened if Courageous or Liberty had just kept our spinnaker poles…?

whistler-32Soon after in the spring of 1984, PLP was contacted by Able Marine in Maine to build some carbon fiber masts for the Whistler 32, a Chuck Paine design that they were building. Actually, PLP had built two sets of masts prior to my working with them, but I conferred with them on a third set. These turned out very well.

I went on to become PLP’s consulting engineer for all their flagpole and lightpole manufacturing. This involved writing the computer program that actually designs the fiberglass laminates for the poles. It took many years of development to program and improve all the computer code. Industry manufacturing standards required full-scale testing, so we instituted a destructive testing program to monitor the strengths and stiffnesses of the poles. This practice and the computer program continue to this day.

corroboree-sailingIn September 1984, I received the commission to design Corroboree, the boat we sail now. Corroboree was built in New Zealand in 1986-87, but her mast was built by PLP in 1988 in carbon fiber. This was just the tube—Hall Spars and Rigging in Bristol, RI, made all the fittings and the boom. When Corroboree partially burned in an unfortunate fire in 1995, PLP built the replacement carbon fiber mast in 1996, and all the fittings were transferred to the new mast.

The Herreshoff and Sparhawk cat ketches

Also in 1984, John Newton of Cat Ketch Yachts Inc. commissioned me to design new composite masts for the Herreshoff cat ketches for four boat sizes of lengths 27’, 31’, 38’, and 45’. The boats were designed by Halsey Herreshoff of the famous Herreshoff line of naval architects, but the original masts were made of wood. They turned out to be quite heavy, and the weights actually varied a lot from boat to boat. John felt that by sticking to more modern composite construction, he could make the masts lighter, stiffer, and more consistent in weight boat to boat, and that’s what transpired. I advocated an oval section for better aerodynamics and uniqueness, and to keep costs low, we used a mix of fiberglass and carbon fiber in the construction. All the Herreshoff designs sported half-wishbone booms which I thought made a lot of sense and adapted to some of my later rig designs.

By 1986, Richard Black came back into the picture with his Sparhawk 36 cat ketch design. He’d had a few of them built in southern California, but was looking for a reliable carbon fiber mast supplier. I put him in touch with John Newton at Cat Ketch Yachts, and they ultimately worked out an agreement whereby Cat Ketch Yachts would not only build all-carbon masts to my design, they would also build the boats. The 36’er was followed by Richard’s Sparhawk 42 in 1988.

herreshoff-cat-ketches sparhawk-36 sparhawk-42

The wood-epoxy and carbon fiber technique

By 1985, I was aware that there weren’t too many builders of carbon fiber masts. The numbers of free-standing rigged boats being built were not great enough to support an independent mast manufacturing effort outside of Freedom Yachts and Cat Ketch Yachts who built their own masts. I decided to develop a construction technique that any do-it-yourself boatbuilder could handle, particularly if they could build in wood-epoxy. In addition, the masts sections did not have to be round, they could be any shape, like an aerofoil or a wing.

I designed elliptical section masts which started out nearly round at first, but became more elliptical as time went on. A round section mast has a lot of form drag, but an elliptical section mast has much lower form drag. Also, engineering with ellipses is really easy — the shape and its strength and stiffness properties are governed by simple equations. This is as opposed to a true aerofoil shape that takes lots of complicated mathematical integration to engineer. That is why all my mast designs are elliptically shaped in section. The result of my effort was an easily-built wood-epoxy mast section that is basically a very lightweight wood mast that is wrapped in carbon fiber.

wood-epoxy-wingmastThis mast building technique was later featured in an article in Professional Boatbuilder magazine, Dec/Jan 92, written by Ted Hugger called Wing Masts. I used this technique for the wingmast on my Deft 25 design, which you can see back in the Boat Designs section.

Various mast designs followed over the next few years, mostly non-rotating free-standing masts. These include a custom design for a 10.43 M cat ketch in New Zealand called Pooh Sticks (1985); production masts for the Sea Pearl 28 by Marine Concepts in Florida (1989); and a custom Craig Walters 49’er called Salt built in North Carolina (1990), to name a few.

Testing in the wind tunnel

During 1985-89, I was commissioned by Robin Lagemann of Cohasset, MA, to design a wingmast for his Bill Peterson-designed 45’ sloop called Ama Heya, an Algonquin name for “water woman.” Robin was very close to the Native American community in southern New England. The boat was wood-epoxy construction being built in Camden, ME, and Robin was going to use it for research on cetaceans (whales). This design was unique for three reasons: First, it was the first time I developed the concept of wingmast/stubmast construction which met Robin’s requirement that there be a fixed point at the top of the mast for lights and other electronic equipment. The stubmast went up through the top of the wingmast and had the ability to hold the top of the headstay at a fixed, non-rotating point. Second, by this construction, the bearings for the wingmast were mounted above deck on the stubmast so that the joint of the stubmast mast at the deck was watertight. And third, we got to test the effectiveness of this design in a wind tunnel, a wonderful opportunity. We did the tests the summer of 1986 at the Wolfson Unit of the University of Southampton in England under the direction of aerodynamicist C.A. (Tony) Marchaj. The photos show Robin Lagemann tending to the model inside the wind tunnel.


Other notable mast designs

naia-1In 1993, I was approached about another unique wingmast project for a 110’ steel charter scuba-diving yacht called Nai’a that sailed out of Fiji in the western Pacific. The owners wanted a wingmast, but could not easily get any carbon fiber. This was to be a stayed rig built on the beach in Fiji in plywood and epoxy. At 99.2’ tall, it was the largest wood-epoxy wingmast in the world and the sixth largest wingmast of any type in the world up to that time.

Project Amazon came along in 1996 (which you can see in the Boat Designs section) which sported two masts each 85’ tall, topping my previous record for height on the Freedom 70. These were followed by Copernicus and Panta Rhei in 1997. Copernicus is a Spencer 42 owned by Bryan and Cary Pollock of Vancouver, BC, Canada. This became the only other mast retrofit project other than Nai’a that I have ever done. Usually, the modifications of a stayed rig boat to a free-standing rig are too expensive and problematic for most owners, but Bryan and Cary were committed. This fixed, non-rotating mast design used the wood-epoxy technique for an oval section which Bryan and Cary built in carbon fiber pre-preg composites on a theater stage in Vancouver. The weight of the mast was within about 5 pounds of the original stayed aluminum mast, but the lack of parasitic drag from no rigging, and its ability to deflect in gusts greatly improved the boat’s sailing ability—sailing faster, pointing higher, and being easier to handle.copernicus-2

Panta Rhei is a 51’ catamaran owned by Allan and Brenda Guenter of Nova Scotia, Canada. They wanted a balestron wingmast wherein the boom extends both forward and aft of the mast to support both the jib and the main. This was similar to the “Aerorig” version (so trademarked) of this type of rig wherein the boom is fixed to the mast. But in Panta Rhei’s version, the boom swivels around the mast on bearings, so the boom and mast are independent of each other, not built as one solid unit like the Aerorig. The upright part of the mast also has its own bearings built into the boat. This was my first of a few balestron designs, and the first that I had done for a multihull.panta-rhei

Wingmast/stubmast design refined & the SAIL magazine award

In 2000, a few years after I designed a new plumb bow for the Freedom 38 Wobegone Daze, owner Dr. Blake Cady of Brooklline, MA, he asked me to redesign the rig to change it from fixed, round free-standing masts to rotating wingmasts. We utilized the wingmst/stubmast idea, but for the booms Blake wanted both wishbones and conventional booms. This made rigging a little more complicated, but it worked. Ted Van Dusen of Composite Engineering in Concord, MA, builder of Project Amazon’s masts, used tooling from the top of those masts to build Wobegone Daze’s masts. The lead photo on this page is of Wobegone Daze.

This new rig was installed in 2001 with very nice sails from Hood Sailmakers. Later that fall, I was inspired to enter Wobegone Daze’s rig design in SAIL Magazine’s Freeman Pittman Innovation Awards contest. Freeman Pittman was SAIL’s Technical Editor for 15 years, and whom I first met at the 1983 Chesapeake Sailing Yacht Symposium where I presented my free-standing mast paper. He later edited a lot of my SAIL magazine articles. Sadly, Freeman succumbed to Lou Gehrig’s Disease in 1996 at the age of 41, and the Innovation Award was named in his honor. I won Honorable Mention at the awards in April 2002, and the judges had this to say about the design:

“This one hit a soft spot, for, as one judge put it, this was exactly the sort if innovation most apt to engage Freeman Pittman’s imagination. The judge’s found designer Eric Sponberg’s new free-standing carbon-fiber wing mast to be a very well thought out and carefully engineered example of a fast, easily handled rig.”

In 2002, my yacht design Saint Barbara came along, which you can read about in the Boat Designs section. That also had a carbon fiber wingmast/stubmast arrangement co-designed by me and owner Sam Kovalak and built by Ted Van Dusen. It worked extremely well — Saint Barbara is a very slick and weatherly boat.

Later wingmast designs

In 2003, my wife and I moved to St. Augustine, FL — it’s a lot like Newport, only warm — and I did not have too many mast designs to do for a few years. I did a speculative design for the Globetrotter 45/Eagle which had my then typical free-standing half-wishbone wingmast rig, but a boat never got built, and I never went through the engineering exercise to do the final design on the masts and booms. See the The Globetrotters page in the Boat Designs section for more details.

GT80-mast-01Then in 2009, I was approached by a project in Belgium to design a wingmast for the GT80 sloop, an Arthur Peltzer design. Again, this mast was the wingmast/stubmast configuration using the wood-epoxy/carbon fiber technique. The mast height was 28.911 meters = 94.86’, my tallest wingmast rig of this style. Unfortunately, I don’t know if this boat and mast were ever completed, so I cannot give any opinion on how well the project worked out.

My final commissioned sailing yacht and mast design came in 2012 with the Globetrotter 66 which, like the Globetrotter 45/Eagle, has a wood-epoxy/carbon fiber free-standing half-wishbone wingmast cat-ketch rig (that seems a mouthful!). Again, the G66 can be seen on The Globetrotters page in the Boat Designs section. To date, this boat has yet to be built.

Conclusions and insights

I am not the only naval architect or boat designer to design free-standing masts and wingmasts, but I was probably one of the most prominent advocates for such rigs. I wrote extensively about them in the yachting magazines, on boat design forums, and on my company website, and judging by the reactions I received, I think I influenced a lot of people into accepting them.

In 2006, I wrote an article on my website called Free-Standing Masts — Some Thoughts on the State of the Art. Not much has changed over the years on this subject, so what I say in that article still pretty much stands.

As a result of my designs and my writing, a lot of potential clients came to me wanting to convert their existing boat from a stayed rig to a free-standing rig, and they asked if I had any stock plans for such a conversion? Although I considered doing stock plans a number of times, I always came back to the realization that masts must be custom-designed to the boat and builder at hand. That calls for a complete design up front, an expensive option on the order of some thousands of dollars instead of some hundreds of dollars. The height, diameter, wall thickness, weight and cost for a mast for any given boat are very likely not at all the same for another boat of the same size — however you define size by length, displacement, sail arrangement and area, or stability. The necessary materials vary significantly all over the world by place and time, and the mast design must be very particular to the materials at hand. Standard designs had few universal applications, and they could be obsolete in a few years. Finally, the skills of one owner could be vastly different from those of another causing much variation in the strength, stiffness, and performance of any given stock mast design.

Sincere there was no reliable way to establish stock mast designs for do-it-yourself builders, I found I had to vet the inquirers and make sure they understood the realities and techniques required for building carbon fiber masts. I certainly did not want them to fall down and kill someone. Added to the cost of making the masts were the necessary changes to the boat itself to accept such rigs, particularly if it was going to be changed from a sloop to a cat ketch. There might be extensive and costly changes to the interior and the deck of the boat and all the associated yard bills that would go along with that. Finally, the old sails could not be used so complete new sails and running rigging added to the costs. Free-standing rigs are a custom market, and therefore, they are expensive. That dampened a lot of enthusiasm to the point that such changes rarely got made. This all holds true even now.

The production market for free-standing rigged boat designs had a surge in the 1970s and 80s under the leadership of Garry Hoyt’s Freedom Yachts and other notables like Nonsuch, Cat Ketch Yachts, and Wylie Cats, the latter being the only one to survive to the 21st century. I address the reasons why in my State of the Art article. Sailboats in general are only about a tenth of the total boating market in the US, and free-standing rigged boats are an even smaller percentage of that. The stayed rig players dominate leaving the free-standing rigged players to be a very small niche, so small that the mast tubes, fittings and parts are not readily available; they have to be custom-made.

Who knows if that will change — I somehow doubt it, not in my lifetime. But I was a player and I think I did some really nice work. And now it is time to practice what I preach—our own boat is my very first commissioned design, Corroboree, with a free-standing sloop rig. It was available and affordable, and so now we’re out there sailing.

Eric W. Sponberg
Naval Architect, retired