As the name suggests, sailboats rely on the power of the wind for propulsion and use a large cloth or synthetic sails for this purpose.
Sailboats are considered to be a separate class of vessels independent of motor-powered crafts since their hydrodynamic characteristics differ.
They can vary in occupancy from single-seater crafts for competition purposes to recreational vessels spanning hundreds of metres that can host up to thirty individuals.
The most common type of sailboat on the market is the small competition variant that is used in sailing competitions around the world. Several international events intended to raise awareness about sailing allow a wide range of craft types to participate including catamarans and cruisers.
For most sailing vessels, sail plans are often drawn up before the vessel leaves port. These plans indicate sail positions for various weather conditions.
In this article, we will go through the various types of sailboats and their key features.
Hull Based Classification Of Sailboats
Sailboats can be classified into three distinct types based on their primary hull design.
- catamarans, and
- multi-hull crafts.
Traditionally, monohulls are the most common design for sailboats since they provide storage in addition to a certain level of vessel stability.
However, with the advent of sailing competitions and an increased focus on the performance and stability features of these crafts, there has been a general shift towards the more favourable catamarans and trimarans.
Monohulls are single-hulled structures, much like conventional vessels, that have a large hull beam (breadth) which provides stability while sailing. The advantage with having a single large hull is that the longer beam allows for improved onboard systems.
Catamarans refer to twin-hulled structures that are attached by specialized members to provide strength. The term originates from the South Indian phrase for “tied pieces of wood”, as this was the manner in which traditional boats were built on the subcontinent.
The advantage of having twin-hulls is that there is an increased level of stability. In addition, if designed properly the vessel will have a much higher speed than conventional crafts owing to lower wetted-surface resistance forces.
On the other hand, extensive care must be taken in designing the vessel, else the resistive forces can exceed the values found in monohulls.
Multi-hull crafts include vessels with anywhere between three to five hulls, although the three-hull variation is the most common. Such crafts are known as trimarans and are considered to be extremely stable owing to their large beam and a lower centre of gravity.
Four and five hulled vessels are more difficult to manufacture and hence are rarely used commercially. An advanced form of the catamaran design is the SWATH version.
SWATH is an acronym for Small Waterplane Area Twin Hull, and it achieves unprecedented levels of speed owing to a considerably small waterplane area. To reduce this area, the hull has a reduced beam above the surface of the water while underwater buoyant structures ensure that the vessel has the necessary weight balance.
Common Monohull Designs
Monohulls are relatively easier to manufacture compared to multi-hull structures. Thus, there has been a wider range of innovation for this type of hull over the last thousand years.
The common classes of monohull crafts are – dinghy, cutter, sloop, catboat, ketch and schooner.
A dinghy is a relatively common sailboat owing to its short overall length and ease of manoeuvring. They are used in competitions and in the port industry.
Generally, dinghies are used to transport people or small cargo to and from a larger vessel such as a cruise ship that is anchored away from the shore.
Such vessels may not be able to enter a port due to size and tonnage regulations. Hence, dinghies serve as the best mode of transporting essential goods between the port and the vessel.
Dinghies can have sails, such as the three-sailed variant consisting of the mainsail, jib and spinnaker. However, motor-powered dinghies are also commonly used especially as life-boats on-board ships.
Cutters are another class of sailboats that are medium-sized and generally have three sails. The main mast on which the sails are mounted is located near the stern of the ship to allow for larger sails to be used.
Cutters were commonly used in competitions as their design favours speed and agility. A different combination of the sails also allows cutters to be used for cruises and other recreational sailboats.
Sloops are similar to cutters and are the most commonly found sailboats. They are the standard in sail designs, with a two-sail configuration used for added manoeuvrability.
In addition to the generic sloop sail configuration, there is also a fractionally-rigged sloop in which one of the sails lies below the top of the mast.
This design allows the crews of smaller sloops to handle the craft while improving performance. Catboats are sailboats equipped with only a single sail. They are aimed at capacity rather than speed and have the mainsail mounted on a single mast.
For increased speeds, sails can be added to the rigging such that wind force is better optimized by the vessel.
The ketch is a sailboat that has two main masts- the main mast located around the midship, and the mizzen mast at the aft. The mizzen mast is generally smaller than the main mast and serves to add speed to the craft. The word ketch is derived from the word catch, denoting the manner in which the sails “catch” the wind as they move.
Schooners are a class of sailboat that can have more than two sails supported on masts known as the main-mast and foremast. The foremast is located near the fore of the vessel and is slightly shorter than the main-mast. In variations where additional masts are added to support more sails, they are positioned such that they remain shorter than the main-mast depending on their sizes.
Keel Based Classification
The keel is the base of a vessel that provides a central backbone for the design of the entire structure. The boat keel is structurally relevant since it often has to carry the weight of the vessel.
In the case of sailboats, the keel is often what the entire craft rests on during transport by road or rail. Thus, keels need to have integral strength and be able to withstand a variety of forces.
Similarly, while sailing, the keel is the lowermost point of the vessel at which resistive forces act. As a result, many modifications are often made to the keel so that hydrodynamic features can be incorporated to reduce drag. Sailboats often sit high in the water owing to their design and shape.
However, for competition and performance crafts, it is essential that they try to sit as close to the surface of the water as possible without capsizing. Thus, the keel often plays the role of a central ballast, by integrating heavy iron or steel components so that the vessel draft increases.
Based on the types of keel, there are several sailing boat variants found in the market. These generally have modified keels for the purpose of improving performance and speed by integrating hydrodynamic features such as hydrofoils.
The types of keels commonly associated with sailboats are as follows: full-length keel, fin keel, centreboard keel, bilge keel, bulb keel and wing keel.
As the name suggests, full-length keels have keels that extend in the form of a long fin below the main structure of the ship. The fin runs along the length of the ship and often has an integrated rudder system attached at the stern.
The advantage of this type of keel is that it is easy to manufacture, with little cost in terms of development. Also, the ballast effect is provided by the extra weight of the full-length keel.
Since it can be difficult to enter certain ports or quays owing to the large draft that comes with this type of keel, manufacturers attempt to reduce fin depth and instead increase its length.
Fin keels, on the other hand, run only along certain regions of the sailboat. Located on the underside of the craft, it sticks out similar to the fin of a fish giving rise to this nomenclature. Since this type of keel must perform the same functions as the full-length keel without having a large length, the fin is deeper.
Owing to this large draft, it may be difficult to dock at certain ports due to depth restrictions. A key feature of this type of keel is that the rudder and manoeuvring systems remain independent of the fin keel, and are located at the extreme aft of the vessel. Centreboard keels are a common feature on high-performance crafts that take part in competitions. They are not restricted to monohull structures and are often found in catamarans and trimarans.
The centreboard keel employs a type of fin that is pivoted about a point on the keel of the vessel. By having a pivot, the natural flow of the vessel and surrounding water varies the depth at which the keel sits below the vessel. Similar to the fin keel, it only runs along a certain length of the vessel.
However, it is distinguished by being able to vary the angle of tilt with respect to the baseline of the craft. In some variations, the crew are able to manually change the angle of tilt, to change performance features during certain events and competitions.
Another variation of the centreboard keel is the daggerboard keel, that allows the fin to completely integrate into the underside of the vessel.
By providing a bay at the underside, the fin can be raised or lowered from the slot. In this type of keel, the raised configuration allows for higher speeds and reduced resistive forces. However, when lowered into the water, the vessel gains added stability and makes up for the loss in speed by improving hydrodynamic features.
Bilge keels refer to protrusions on the sides of the hull of the vessel, commonly called the bilges. These protrusions run along the length of the vessel while tapering into the hull panels at both ends.
The primary purpose of bilge keels is to improve the rolling stability of the craft. The fins stick out perpendicular to the hull and can vary in length depending on the purpose. For instance, sailboats require larger anti-roll stability, and hence have long tapering bilge keels.
The bilge keels must be symmetrically placed on both the port and starboard sides, so as to ensure even hydrodynamic characters.
A bulb keel is a protrusion sticking vertically below the craft and terminating in an oblong-shaped hydrodynamic device called the bulb. The bulb acts as a 3D hydrofoil that improves stability and handling of the vessel. Due to the increased wetted surface area, there is a slight drop in the speed, but it can be made up through the superior handling capabilities.
For smaller crafts, longer bulb keels are required, and as this length increases, a chance of accidental grounding of the vessel increases.
The last commonly found type of keel is the wing keel. The wing keel is similar to the bulb keel, except that instead of a bulb terminating a vertical protrusion, there are horizontal hydrofoils extending from the central shaft.
The primary purpose of the wings underneath the ship is to improve handling and stability. In addition, they slightly lift the craft above the surface of the water. As a result, the total wetted surface area remains constant and may even decrease. Thus, speed remains constant and may improve as the craft picks up velocity.
Mast Based Classifications
The mast of the vessel refers to a vertical shaft extending out of the deck which supports the sails and rigging. Older models of sailboats and ancient ships had masts constructed out of wood, while modern speed-oriented versions use galvanized steel or aluminium.
Aluminium has the benefit of being extremely light while still retaining its strength, which is important during harsh weather conditions.
The various mast-based classification includes – sloop, fractional-rig sloop, cutter, ketch, schooner and catboat.
The sloop is the most common mast type, where a single mast supports two sails called the headsail (or foresail) and the mainsail.
The headsail also goes by different names depending on the purpose and configuration of the sails.
In a fractional rig sloop, the forestay cable that is used to hoist the headsail is actually placed below the top of the mast. This configuration is particularly useful when it comes to performance, as the tip of the mast can be hauled towards the aft using stiff cables, and the sails can be collapsed.
This is useful on days when wind power can be used to propel the sailboat, without the sails had to be fully extended.
Another useful feature of being able to trim or flatten the sails is that during particularly strong squalls of wind, the sails will not be punctured or ruptured due to the high wind pressure. The next type of mast configuration is the cutter. This involves a single mast supporting three sails- one mainsail, and two headsails known as the staysail hauled by the inner stay cable, and the jib hauled by the headstay cable.
The mast is located more towards the aft compared to the sloop, to allow for an easily manoeuvrable configuration. In addition, a wide range of sail arrangements makes it favourable for cruise operators and for competition purposes.
The ketch has a two-mast configuration, with the aft mast known as the mizzen mast. The mizzen mast is located fore of the rudder post, and aft of the main mast.
The mizzen sail rests on the mizzen mast. In general, the mizzen mast is slightly shorter than the main mast.
The main mast supports two sails known as the mainsail and the headsail.
The schooner is another configuration similar to the ketch, but where the aft mast is taller than the foremast.
Schooners can have multiple masts and are not restricted to commercial small and medium sailboats. The images of ancient ships that were used for trade and military purposes were often schooners having between four to six masts with an average of over ten sails each.
In addition, the sails of the schooner tend to lie along the length of the vessel, rather than along the beam. This is to prevent sail rupture during violent storms or during heavy winds. The catboat is one of the simplest configurations where only a single sail and mast arrangement are used.
The mast can be located either aft or fore of midships, with varying advantages to each configuration. The ease of design and construction makes it a favourable sailboat for beginners and trainees. However, the disadvantage behind the catboat is that the sail cannot be used to move against the direction of the wind, unlike other sail variations.
Apart from recreation purpose, sailboats are one of the most common types of vessels used in recreational purposes and for competitions. They can vary in the hull, keel and sail configurations based on the primary purpose that they are intended to be used for.
For over five thousand years, sailboats have been in use, whether it has been for transportation in Ancient Egypt, or for sailing events in modern times. Technological advancements have turned the sailboat into a sleek, agile and fast vessel capable of reaching extremely high speeds by harnessing the power of the wind.
Whether it be for cruises or for racing events, sailboats and other such crafts continue to be a favourite choice for sailors.
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