“America” – ©Detroit Photographic
Humans have been sailing the seas for a very long time. In the beginning, boats ventured at sea for fishing, but they were also the only means of transportation and connection between islands. As ships increased in dimension, they also started to be used for warfare. Ships became a means for transporting goods at sea or on rivers and eventually also for moving passengers. Over time, the reasons for shipbuilding have changed, and so have design, materials and construction techniques of vessels. Commercial objectives drove shipbuilders’ choices. Onboard comforts and aesthetics were not a priority.
It is also worth remembering that until around the 1700 there were no schools of shipbuilding, designs or rules, and all knowledge was passed down orally by skilled shipbuilders. The construction of a ship is an ancient craft which did not evolve much for centuries.
The advent or recreational sailing drastically changed things. Sailing for pleasure is a recent practice. It is only in the course of the last two centuries that navigation for pleasure or sports did start.
So it was that in 1851 the schooner “America” of the New York Yacht Club challenged 15 yachts of the “Royal Yacht Squadron” in the annual race around the Isle of Wight. The prize was the “100 Guinea Cup”. Two different construction philosophies were at a clash: the English believed that ships, to be fast and sea-worthy, had to be narrow and with deep keels, focusing on weight stability. Their search for speed resulted in the construction of the legendary clippers. Lets not forgeet that, In the second half of the 1800s, there were two main commercial routes: from China to England for tea and from Australia to England for wool. The ship that reached the destination port first would achieve the highest selling price for its cargo. Therefore, speed was essential.
Americans thought stability resulting from hull shape was the key, focusing on wider and lighter boats and, above all, shallower keels. Their search for speed developed through the experience of vessels dedicated to fishing: the glorious Bankers – so-called because they were used for fishing trips on the infamous banks of Newfoundland. Fishing boats with their catch had to reach the markets of the main cities along the coast as fast as possible, to beat the competition and obtain the best-selling prices. Thus boats had wide and shallow hulls.
Now back to the Isle of Wight. The schooner “America” finished the race 8 minutes ahead of its closest rival, ensuring victory and marking the beginning of one of the longest-standing competitions in sports, the “America’s Cup”. It was also the beginning of a continuous cycle of nautical design innovation.
The ships of that era all had continuous keels, a large appendage that connected the bow to the stern. The keel contained the ballast to achieve the desired stability calculated in relation to boat length and sail area. The materials used for construction were mainly wood and, to a lesser extent, iron. Boats were heavy displacement with immersed sections of the hull of significant volumes. The design of the keels of that time had generous front sections. As a result, the wet surface was large, offering significant resistance to advancement.
The sharp bow that distinguisched Schooners was the leading edge of this huge appendage that continued to a wide maximum beam before ending at its trailing edge with the rudder blade, which was a continuation of the keel. The shaft of the rudder was inclined with respect to the vertical plane of the boat. As the angle of incidence of the blade changed with the flow of the water, this misalignment generated a lateral force affecting the displacement of the bow as well as an undesired vertical vectorial component that slowed down the vessel. An underwater design of this type tended to reduce the governability of the boat whilst ensuring high stability of their course, reducing the yaw to a minimum and allowing these boats to sail upwind at angles close to 60°, remarkable values for the rigs of the time.
In the first half of the last century, boats began to be larger and more performant, thanks to new construction materials such as steel and alloys. Advancement relied on the first experiments in naval tanks used to carry out hydrodynamic tests of scale models to obtain information on the best configuration and optimal ratio between propulsive force and resistance.
Racing regulations were based solely on the length at the waterline and the sail area. So keels began to be shorter and shorter with yacht having long and thin overhanging bows and sterns. As the boats became too extreme and dangerous, a new method of classification for racing boats came into effect, the Universal Rule. As a result, the famous J-Class was born. By 1930, these boats were equipped with instruments designed for aeroplanes to measure the speed through water and wind speed.
Soon later, the first ‘fin’ keels appeared. Construction materials included iron or lead, cast or rarely machined by CNC. The keel constituted the ballast of the boat lowering its centre of gravity. The profile gave good performance when close-hauled with improved manoeuvrability. The large base plate securing the keel to the hull made them relatively resistant to impacts.
‘L’ shaped keels are an evolution of the initial fin design, with a thinner and longer wing-like profile concentrating the weight of the ballast in the ‘shoe’. Increasing the draft improved the righting moment and increased the performance both upwind and when reaching.
A further advancement of the design was the ‘T’ shaped keel, with the centre of gravity even lower, and the appearance of bulbs, shaped to reduce the vortices created on the vertical fin.
The transformation of the rudder went hand in hand with the evolution of the keels. Initially, rudder blades hinged onto the “skeg”, which was a structural part of the hull which also supported and protected the rudder in case of impacts.
The large loads affecting all the steering system led designers to oversize components, penalizing the hydrodynamic efficiency in a crucial area of the boat. One solution was the reduction of the size of the skeg, and an increased surface of the rudder blade. However, the real revolution came with the total elimination of the skeg. The rudder now relied exclusively on its own shaft for support, made of high-strength steel.
To mitigate the water force on the shaft, designers solved the dynamic imbalance through pressure compensation elements, optimizing the balance between the portion of the blade in front and aft of the rotation axis.
Most of the yachts that will start in the early groups of the Global Solo Challenge will be equipped with the types of appendages just described. In a further article, we will analyze later evolutions in the designs that we can find on some of the more performant boats entered in the event.
