Sailboats are made in a tremendous variety of sizes, from 10 feet (or less) to a hundred feet or more.
So the bigger they are, the faster they go.
Here’s Whether or Not Bigger Sailboats go Faster:
Usually, a bigger sailboat will go faster than a smaller one of similar construction. Waterline length is a prime determinant of a boat’s speed. Also: hull shape, the amount of wetted surface area, weight aloft, the number of hulls, and whether the boat is a foiling boat.
Monohull, Multihull, and Hydrofoil Designs Have Different Impacts on Speed:
It can be tricky to claim that bigger is faster, as multi-hull sailboats go faster than much larger monohulls, usually about 20-30% faster.
Their comparatively thinner hulls have much less wetted surface, and therefore less drag, than boats with much longer waterlines. This is particularly true when a catamaran is flying a hull, as there is even less drag.
Hydrofoiling sailboats are another exception to the general rule of waterline length, as they have so little surface area actually in the water. Even a tiny, 15-foot foiling Moth will go faster than many 30-foot monohulls.
However, larger foiling boats will almost always go faster than smaller foiling boats, as their larger rigs generate more power versus the amount of foil they have in the water.
How Does the Size of a Sailboat Impact its Speed?
Keeping in mind that there are other factors, the waterline length of a boat determines the length of the wave that it generates.
This is a concept called hull speed.
When a boat has reached hull speed, there is a wave crest at the bow being pushed, a trough in the middle, and another wave crest at the stern. In practical terms, its speed has created a wave that is equal to its own waterline length.
The longer the generated wave is, the faster the boat is going. Since a longer wave means a higher speed, the longer boats will create bigger waves and go faster.
When it has reached its hull speed, that is the theoretical maximum it can attain. That was true for centuries, as the larger sailing vessels could not exceed a certain speed.
That changed in the 20th century with expanding the recreational sailing market, and design limits were pushed. Boats that were beam-reaching under spinnaker routinely exceeded their hull speed, particularly when surfing larger waves.
They were able to get over the waves and start planing.
Hull speed was an observational concept, and naval design uses a broader speed/length ratio design formula. Hull speed fits into this larger concept and is the square root of anywhere from 1.3 to 1.5 times the hull length; usually, it is 1.34.
So a sailboat with a 20-foot waterline generating a 20-foot wavelength would have a hull speed of about 6 knots; a sailboat with a 40-foot waterline/wavelength would have a hull speed of about 8.5 knots.
Other factors are considered, such as displacement and sail area, but waterline length is where the boat’s base speed is established in a monohull.
Hull shape will affect this, though. One reason for the J/24’s popularity when it was widely introduced in 1977 is that the hull design was such that it regularly went faster than larger boats.
Later designs like the Melges 24 were even faster, leaving 30-foot boats behind routinely, as these boats could get up on a plane regularly.
In mentioning planing, we must bring up windsurfing here. Their length is completely irrelevant to their speed in comparison to monohulls and even multihulls. They can reach speeds above 20 knots fairly easily.
In fact, windsurfers held the world speed records in the mid- 2000s, of up to 49.09 knots. Because they are planing craft, they do not generate their own waves and are not regulated by the hull speed concept.
Do Fast Sailboats Use Special Sails?
Sails have been made out of a variety of materials over the years.
Up until the early 1960s, canvas was the traditional material for sails, with Egyptian Cotton, in particular, favored by many sailors.
But that material was prone to stretching, often to the point of no return. Polyesters like Dacron became the dominant fabric then and now are considered to be a traditional fabric.
Racers, however, began looking for different materials that had better shape retention and less weight aloft. This led to laminate fabrics, mostly using Kevlar early on, but then other threads such as Spectran, carbon, and even more specialized polyester.
Today the fast sailboats use almost exclusively laminate sails. These are generally made by having a layer of Mylar and laying threads over it in the direction you want the strength. These are laminated with another layer of mylar.
It used to be that this material came in 36- or 54-inch rolls, but now it is common to see a sail being one entire laminated sheet. This is done by having a mold of a sail done at a factory, and the laminate layers laid and bonded over the top of it.
This used to be a costly process, but the technology is more common now. Some sailmakers even make this style in three or four sections, so there are only a few seams in the entire sail.
More exotic are the wing sections being used by the fastest boats, such as the foiling catamarans used in recent America’s Cup competitions. These are hard, two-part sails.
The front part of the forward structure is made from carbon and replaces the traditional mast; the rest of the “sail” comprises 2 honeycomb structures, made of carbon and Kevlar and covered in a powerful film called Klysar.
Those boats are the cutting edge of speed technology and continue to evolve. Foiling boats such as these have rewritten the design books, as they have so little wetted surface area compared to their sail area and the lift they generate.
How Fast Do Big Sailboats Go?
Current marine architecture has produced hulls that routinely exceed their projected hull speed.
The fastest monohulls are the boats designed for the various offshore ocean races, such as the Volvo Ocean Race, which goes worldwide. They can reach speeds of 36 knots or more, though the average is in the low- to mid-20s.
The distance-sailing catamarans are capable of reaching speeds of 45 knots regularly, and sometimes more.
The hydrofoiling catamarans of recent America’s Cup campaigns are high-speed boats. They can attain speeds above 30 knots routinely and get over 40 knots in the right conditions.
It is worth pointing out here that these boats go so fast that they feel to the crew that they are experiencing storm winds because of the apparent winds they generate. There might be only 18 knots of breeze on the water, but it will feel as if they are in 50 knots of wind to the crew of a foiling boat.
The new America’s Cup boats will be the AC75, a foiling monohull. It remains to be seen the speeds this design can attain.
What Are the Fastest Sailboats?
For monohulls, the 100-foot long Comanche is one of the fastest in the world.
In the 2016 Transatlantic Race, she averaged 25.75 knots in a 24-hour period, covering 618 nautical miles, still a record for monohulls.
The F-50 catamaran from Australia reached a top speed of 49.7 knots for multihulls in 17 knots of breeze. Once the boat is fully developed, it is expected to reach speeds above 50 knots.
The AC50 America’s Cup foiling catamaran Patriot reached 53.3 knots in a bear away, shortly before being eliminated in competition; that is the fastest recorded speed for those boats.
The Vestas Sailrocket 2 is a uniquely designed 40-foot hydrofoiling catamaran created to break the speed record. In 2012, it ran a 500-meter course at 65.45 knots, with a peak of 68.01 knots. Both of these speeds world records.
She also broke the nautical mile speed record, setting a new record of 55.35 knots over that distance.
The team is building another vessel to break those records, and that they hope to have it ready in 2022.