The world of yacht design has gone through a major upheaval in the decade of the l980s. Following the disastrous Fastnet race of 1979, so well documented and analyzed by John Rousmaniere in his book Fastnet Force 10, many leading designers and sailors began to question the direction of design trends.

During that race, a Force 10 gale (48 to 55 knots) hit the fleet of 303 boats that was racing from the southern England, around Fastnet Rock off the southern tip of Ireland. From surveys taken by race organizers and from interviews performed by Rousmaniere in preparation for writing his book, some very disturbing statistics came to light.

It is estimated that at least 18 boats were rolled a full 360 degrees. Twenty four boats were abandoned, five sank and approximately 170 were rolled over until their masts hit the water. Also, it was reported that five boats became inverted — turned turtle — and remained upside down for periods between 30 seconds and five minutes. Lastly, and tragically, fifteen sailors lost their lives to drowning or hypothermia.

The Cruising Club of America, which was preparing to run their biennial Newport-Bermuda Race in the spring of 1980, took a hard look at the Fastnet race and began to study what could be done to prevent such a disaster from reoccurring.

The CCA's Technical Committee joined forces with the Technical Committee of the Measurement Handicap System (MHS) to see what caused the Fastnet disaster. Several experts in the field of yacht design and marine engineering became central players in a study that was to last for five years. Karl Kirkman, chairman of the Sailboat Committee of the Society of Naval Architects and Marine Engineers, yacht designer Olin Stephens, Richard McCurdy, Chairman of the Safety At Sea Committee of the United States Yacht Racing Union, and Dan Strohmeier, who was a former president of SNAME, all undertook the various tasks of analyzing the design attributes, weather attributes and safety preparations. The primary focus of the study was to determine how and why so many boats capsized.

In 1985 a final report was issued by USYRU and SNAME's Joint Committee on Safety From Capsizing. The 66-page document, which is available from the United States Yacht Racing Union (P.O. Box 209, Newport, Rhode Island 02840), details the research undertaken by the joint committee and offers several broad conclusions that help illuminate what is safe and what is not in hull and yacht design. While the focus of the work was primarily to assess the capabilities — the likelihood of capsize — on boats designed under the various racing rules, IOR, IMS and the old CCA rule, the conclusions should affect the way all sailors think about design.

The conclusions of the report, in brief, are:
— Larger boats are less prone to capsize than smaller boats.
— A dismasted sailboat is more likely to capsize than a boat carrying her full rig.
— A boat has an inherent stability range, ie. an angle of heel past which it will capsize. That stability range can be calculated from the boat's lines and specifications.
— Some modern boats, which have been designed to the IOR, or are designed to be particularly beamy, may remain inverted following a capsize. Boats with a stability range under 120 degrees may remain inverted for as long as two minutes.
— Boats lying sideways to a sea, particularly light, beamy vessels, are more likely to capsize than boats that are held bow to the sea or stern to the sea. It follows, then, that boats that are sailed actively in gale conditions and breaking seas are more likely to avoid capsize than those left to lie untended, beam to the seas.

The issue of whether or not a boat will capsize, and when and how it might suffer such a fate, is a key point for any sailor contemplating safe extended coastal or offshore cruising. By analyzing a boat's stability range, you can get a very good reading on how the boat will handle a gale at sea and how best to plan you own gale tactics. The Joint Committee sought a simple way for boat owners to arrive at a usable measurement of their boat's stability range.

The best approach is to have your boat — or prospective boat — measured by an IMS measurer. From the measurements, the USYR measurement team can then calculate the boat's stability range. The USYRU has a record of many production boats already measured, so it may be possible to purchase the IMS information, containing the stability information from the Union.

Another approach is to use the simple Capsize Screening Formula, derived by the committee for use by average sailors who do not have access to IMS measurements and do not own a boat already on the USYRU's list. The formula, which assumes that the vessel in question is of a fairly standard type and of a size suitable for offshore sailing, gives a general guide to a boat's stability. The number played out by the formula is the result of comparing the boat's beam with its displacement, for excessive beam has been shown to contribute to a lack of ultimate stability , while displacement can be a determining factor in improving stability. The formula is as follows:

Capsize Screening # = Boat's Max. Beam (feet) / Cube Root (Gross Displacement / 64)

In English: Take the boat's gross displacement (in pounds), divide it by 64 and then take the cube root of the quotient. Now, take that cube root and divide it into the boat's maximum beam (in feet). The resulting Capsize screening number should be 2 or less. In general, if the number is over 2, the boat fails the screen. If the number is under 2, the boat passes.

Using the Capsize Screening Formula, you will be able to get a quick idea of a boat's stability. However, you will want to explore the boat's full capsize characteristics before you decide to purchase it and set off sailing in open waters.

Assessing a boat's stability range will give you a good idea of how the boat will behave in the worst conditions. But, when looking at a boat's design with safety in mind, it is essential to evaluate both the hull design in general and specifically.

The trend to light, fast hulls that has dominated cruising and racing boats since the late 1960s, has provided sailors with boats that offer a high level of performance and ample accommodations. The evolution of hull design from full keels with keel-hung rudders has been a function of building materials and engineering as much as it has been due to innovation on the part of designers. In the 1880s Nathaneal Herreshoff, the Wizard of Bristol, developed what may be the first small sailing vessel with a fin keel and spade rudder. He discovered that the performance of such a hull configuration outperformed every other design option of the time. Yet, a split keel and rudder did not find its way into wide use until the advent of fiberglass materials and the engineering made possible by the material.

Traditional boats of today, boats with full keels, keel-hung rudders and their propellers in an aperture, are descendants of working craft from a hundred years ago. The design is noted for its sea kindliness, it's ability to carry heavy loads, and its slow and deliberate motion through the water. The design type evolved at a time when all boats were built of wood. The simple engineering dictates of constructing a seaworthy sailing vessel in wood led designers and builders to craft the full-keel designs we know today. In fact, the reason Nathaneal Herreshoff's early fin keeler did not lead to similar designs in larger, ocean going vessels was simply because the materials required to make such a vessel strong, seaworthy and safe did not exist at the time.

Yet, small boat-design quickly followed Herrshoff's lead. The Star boat, the 110 and 210 and other one-designs have long distinguished histories. All three are fin-keelers with spade rudders. But it was not until the l960s that larger boats, ocean sailing boats, could be engineered safely using the split design type. William Lapworth's Cal 40, designed in the early 1960s, led the way by acquitting itself as a very fast sailing boat around the buoys, a winner of offshore races and, importantly, a safe and sea kindly vessel. The design of the Cal 40 was made possible by the extraordinary strength and forming abilities of fiberglass construction. The material permitted imaginative designers to seek new ways to make sailboats go fast, and new ways to combine speed and comfort.

The concepts behind the split keel and rudder design type gained even more notoriety and popularity when Olin Stephens created the successful America's Cup defender Intrepid. Unlike her competitors in that season, Intrepid had a stubby fin keel, a bustle under the after quarters and had her rudder mounted at the end of the bustle well aft. Intrepid was unbeatable. The success of the Cal 40 and of Intrepid opened many designer's and builder's eyes to the performance advantages of the fin keel, spade rudder design type. It was not long after that such designs became the standard, both among modern cruising boats and the racing fleet.

There is little argument today that the split keel and rudder configuration produces boats faster than configurations of the more traditional type. If speed is the first prerequisite in a boat, then lightness, minimum wetted surface and a spade rudder/fin keel design is the way to go. Yet, for those who will be sailing in conditions other than pure drag racing around the buoys there are other considerations that must go into the selection of the right boat. The sailor who is contemplating sailing long distances along a coast or making offshore passages must look for design qualities that enhance seaworthiness, stability, the ability to carry the loads of gear, water and fuel and the ability to be handled by a small — often two-person — crew, as well as speed through the water.

The lessons learned from the 1979 Fastnet cast a pall over the design evolutions of the IOR. The work done by the Joint Committee on Safety From Capsizing is a monument to the thought that has gone into yacht design during the 1980s. The outcome has been a consensus among the leaders in naval architecture, in race organization and among the leading boat builders. At the beginning of the 1990s, sailors looking for suitable, safe boats in which to go to sea inherit the benefit of all the thought and work that has taken place. New boats coming into the market are being conceived to be stable in bad weather, to be sea kindly and to be rigged for short-handed sailing. Safety, although not heralded by boat builder's promotion or by the sailors, is the big winner. And, as the IOR slowly fades away, to be replaced by the IMS, sailors around the world will find ever increasingly that boats brought to them by designers and builders conform to the latest and best thinking in the safety at sea category.