The keel is the bottom-most longitudinal structural element of a watercraft. On some sailboats, it may have a hydrodynamic and counterbalancing purpose as well. The laying of the keel is often the initial step in constructing a ship. In the British and American shipbuilding traditions, this event marks the beginning date of a ship's construction. [1]
The word "keel" comes from Old English cēol, Old Norse kjóll, = "ship" or "keel". It has the distinction of being regarded by some scholars as the first word in the English language recorded in writing, having been recorded by Gildas in his 6th century Latin work De Excidio et Conquestu Britanniae , under the spelling cyulae (he was referring to the three ships that the Saxons first arrived in). [2] [3]
Carina is the Latin word for "keel" and is the origin of the term careen (to clean a keel and the hull in general, often by rolling the ship on its side). An example of this use is Careening Cove, a suburb of Sydney, Australia, where careening was carried out in the early colonial days.
The use of a keel in sailing vessels dates back to antiquity. The wreck of an ancient Greek merchant ship known as the Kyrenia ship establishes the origin of the keel at least as far back as 315 BC. [4] [ page needed ] The Uluburun shipwreck (c. 1325 BC) had a rudimentary keel, but it may have been more of a center plank than a keel. [5]
In carvel-built hulls, construction began with the laying of the keel, followed by the stern and stem. Frames were set up afterward, set at key points along the keel. Later, the keelson was attached to the keel, either bolted or with treenails. [6]
A plank first building system that is still in use today is clinker construction, using overlapping planks which are shaped to produce the hull form. Older systems include the bottom-based method used for the planking on either side of the keel of a cog (and also in Dutch shipbuilding up to and including the 17th century). This involves flush-fitted planks that have been cut to provide the shape of the hull. Still older is the mortice and tenon edge-to-edge joining of hull planks in the Mediterranean during the classical period. In this system, much of the strength of the hull is derived from the planking, with the frames providing some extra strength. In all these systems, the joining of the keel, stem and sternpost are the starting point of construction. [6]
A structural keel is the bottom-most structural member around which the hull of a ship is built. The keel runs along the centerline of the ship, from the bow to the stern. The keel is often the first part of a ship's hull to be constructed, and laying the keel, or placing the keel in the cradle where the ship will be built, may mark the start time of its construction. Large, modern ships are now often built in a series of pre-fabricated, complete hull sections rather than being built around a single keel, so the shipbuilding process commences with the cutting of the first sheet of steel. [7]
The most common type of keel is the "flat plate keel", which is fitted in most ocean-going ships and other vessels. A form of keel found on smaller vessels is the "bar keel", which may be fitted in trawlers, tugs, and smaller ferries. Where grounding is possible, this type of keel is suitable with its massive scantlings, but there is always a problem of the increased draft with no additional cargo capacity. If a double bottom is fitted, the keel is almost inevitably of the flat plate type, bar keels often being associated with open floors, where the plate keel may also be fitted.[ citation needed ]
Hydrodynamic keels have the primary purpose of interacting with the water and are typical of certain sailboats. Fixed hydrodynamic keels have the structural strength to support the boat's weight. [8]
In sailboats, keels serve two purposes: 1) as an underwater foil to minimize the lateral motion of the vessel under sail (leeway) and 2) as a counterweight to the lateral force of the wind on the sail(s) that causes rolling to the side (heeling). As an underwater foil, a keel uses the forward motion of the boat to generate lift to counteract the leeward force of the wind. As a counterweight, a keel increasingly offsets the heeling moment with increasing angle of heel. Related foils include movable centreplates, which -being metal- have the secondary purpose of being a counterweight, and centreboards and daggerboards, which are of lighter weight, do not have the secondary purpose of being a counterweight.
Moveable sailboat keels may pivot (a centreboard, centreplate or swing keel), [9] retract upwards (lifting/retracting keel or daggerboard), [10] or swing sideways in the water (canting keels) to move the ballasting effect to one side and allow the boat to sail in a more upright position. [11]
A hull is the watertight body of a ship, boat, submarine, or flying boat. The hull may open at the top, or it may be fully or partially covered with a deck. Atop the deck may be a deckhouse and other superstructures, such as a funnel, derrick, or mast. The line where the hull meets the water surface is called the waterline.
A yacht is a sail- or motor-propelled watercraft made for pleasure, cruising, or racing. There is no standard definition, though the term generally applies to vessels with a cabin intended for overnight use. To be termed a yacht, as opposed to a boat, such a pleasure vessel is likely to be at least 33 feet (10 m) in length and may have been judged to have good aesthetic qualities.
A sailboat or sailing boat is a boat propelled partly or entirely by sails and is smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by region and maritime culture.
A daggerboard is a retractable centreboard used by various sailing craft. While other types of centreboard may pivot to retract, a daggerboard slides in a casing. The shape of the daggerboard converts the forward motion into a windward lift, countering the leeward push of the sail. The theoretical centre of lateral resistance is on the trailing edge of the daggerboard.
The koch was a special type of small one- or two-mast wooden sailing ships designed and used in Russia for transpolar voyages in ice conditions of the Arctic seas, popular among the Pomors.
Carvel built or carvel planking is a method of boat building in which hull planks are laid edge to edge and fastened to a robust frame, thereby forming a smooth surface. Traditionally the planks are neither attached to, nor slotted into, each other, having only a caulking sealant between the planks to keep water out. Modern carvel builders may attach the planks to each other with glues and fixings. It is a "frame first" method of hull construction, where the shape is determined by the framework onto which the planks are fixed. This is in contrast to "plank first" or "shell first" methods, where the outer skin of the hull is made and then reinforced by the insertion of timbers that are fitted to that shape. The most common modern "plank first" method is clinker construction; in the classical period "plank first" involved joining the edges of planks with mortise and tenon joints within the thickness of the timbers, superficially giving the smooth-hull appearance of carvel construction, but achieved by entirely different means.
Boat building is the design and construction of boats — and their on-board systems. This includes at minimum the construction of a hull, with any necessary propulsion, mechanical, navigation, safety and other service systems as the craft requires.
A centreboard or centerboard (US) is a retractable hull appendage which pivots out of a slot in the hull of a sailboat, known as a centreboard trunk (UK) or centerboard case (US). The retractability allows the centreboard to be raised to operate in shallow waters, to move the centre of lateral resistance, to reduce drag when the full area of the centreboard is not needed, or when removing the boat from the water, as when trailering. A centreboard which consists of solely a pivoting metal plate is called a centerplate; the term "centreboard" may refer to either a wooden or a metal pivoting retractable foil. A daggerboard is similar but slides vertically rather than pivoting.
A monohull is a type of boat having only one hull, unlike multihulled boats which can have two or more individual hulls connected to one another.
This glossary of nautical terms is an alphabetical listing of terms and expressions connected with ships, shipping, seamanship and navigation on water. Some remain current, while many date from the 17th to 19th centuries. The word nautical derives from the Latin nauticus, from Greek nautikos, from nautēs: "sailor", from naus: "ship".
Proas are various types of multi-hull outrigger sailboats of the Austronesian peoples. The terms were used for native Austronesian ships in European records during the Colonial era indiscriminately, and thus can confusingly refer to the double-ended single-outrigger boats of Oceania, the double-outrigger boats of Island Southeast Asia, and sometimes ships with no outriggers or sails at all.
Clinker-built is a method of boat building in which the edges of hull planks overlap each other. Where necessary in larger craft, shorter planks can be joined end to end, creating a longer strake or hull plank.
A leeboard is a form of pivoting keel used by a sailboat largely and very often in lieu of a fixed keel. Typically mounted in pairs on each side of a hull, leeboards function much like a centreboard, allowing shallow-draft craft to ply waters fixed keel boats cannot. Only the leeward side leeboard is used at any time, as it submerges when the boat heels under the force of the wind.
The winged keel is a sailboat keel layout first fitted on the 12-metre class yacht Australia II, 1983 America's Cup winner.
A chine in boat design is a sharp change in angle in the cross section of a hull. The chine typically arises from the use of sheet materials as the mode of construction.
A bilge keel is a nautical device used to reduce a ship's tendency to roll. Bilge keels are employed in pairs. A ship may have more than one bilge keel per side, but this is rare. Bilge keels increase hydrodynamic resistance, making the ship roll less. Bilge keels are passive stability systems.
A sailing yacht, is a leisure craft that uses sails as its primary means of propulsion. A yacht may be a sail or power vessel used for pleasure, cruising, or racing. There is no standard definition, so the term applies here to sailing vessels that have a cabin with amenities that accommodate overnight use. To be termed a "yacht", as opposed to a "boat", such a vessel is likely to be at least 33 feet (10 m) in length and have been judged to have good aesthetic qualities. Sailboats that do not accommodate overnight use or are smaller than 30 feet (9.1 m) are not universally called yachts. Sailing yachts in excess of 130 feet (40 m) are generally considered to be superyachts.
A trailer sailer is a type of sailboat that has been designed to be easily transported using a boat trailer towed by an automobile. They are generally larger than a sailing dinghy. Trailer sailers include day sailers and small cabin cruisers, suitable for living on.
The Humber keel was a type of single-masted, square-rigged sailing craft used for inshore and inland cargo transport around Hull and the Humber Estuary, in the United Kingdom, particularly through the late 19th and early 20th centuries.
The following outline is provided as an overview of and topical guide to sailing:
