A multihull is a ship or boat with more than one hull, whereas a vessel with a single hull is a monohull. Multihull ships can be classified by the number of hulls, by their arrangement and by their shapes and sizes; the first multihull vessels were Austronesian canoes. The builders hollowed out logs to make canoes and stabilized them by attaching outriggers to prevent them from capsizing; this led in due course to the proa and trimaran. In Polynesian terminology the catamaran is a pair of Vaka held together by Aka, whereas the trimaran is a central Vaka, with Ama on each side, attached by Aka. Catamarans and trimarans share the same terminology. Ama −. Aka −. In Hawaiian, this is called the iako. Vaka −. Modern pioneers of multihull design include James Wharram, Derek Kelsall, Tom Lack, Lock Crowther, Hedly Nicol, Malcolm Tennant, Jim Brown, Arthur Piver, Chris White, Ian Farrier and LOMOcean The vast majority of multihull sailboats are catamarans. Trimarans are less common, proas are unknown outside the South Pacific.
An outrigger canoe is a canoe with a slender outrigger attached by two or more struts. This craft will be propelled by paddles. If the craft has a sail, it is known as a proa. While canoes and proas both derive stability from the outrigger, the proa has the greater need of the outrigger to counter the heeling effect of the sail; the difficulty with the proa is that the outrigger must be on the lee side to be effective, which means that a change of tack will need the sail to be rearranged. A catamaran is a vessel with twin hulls. Commercial catamarans began in 17th century England. Separate attempts at steam-powered catamarans were carried out by the middle of the 20th century. However, success more developed hydrodynamic technologies. During the second half of the 20th century catamaran designs flourished. Nowadays, catamarans are used as racing, sailing and fishing boats. Cruising catamarans are becoming important in the holiday charter market; some 70% of fast passenger RoRo ferries are catamarans.
The hulls of a catamaran are connected by a bridgedeck, although some simpler cruising catamarans have a trampoline stretched between the crossbeams. Small beachable catamarans, such as the Hobie Cat have only a trampoline between the hulls. Catamarans have no ballast and their stability is derived from the width between the hulls; the distance between hulls is called the "transverse clearance", the greater this distance, the more stable the catamaran will be. A catamaran's hulls are slim. Catamarans are prone to "slamming", an unpleasant phenomenon where the waves slam against the underside of the bridge deck; the distance between the design waterplane and the bottom of the bridgedeck is called the "vertical clearance". Although a large vertical clearance increases a catamaran's seaworthiness, the designer must take care not to raise the overall CoG too much. A trimaran is a vessel with three hulls. Unlike a catamaran where the hulls are mirror-images of each other, a trimaran is rather like a monohull with two slim outriggers.
A trimaran has less accommodation space than a catamaran, but may be capable of faster speeds. The trimaran has the widest range of interactions of wave systems generated by hulls at speed; the interactions can speed. No authentic trimarans exist. Model test results and corresponding simulations provide estimates on the power of the full-scale ships; the calculations show possible advantages in a defined band of relative speeds. A new type of super-fast vessel, the wave-piercing trimaran is known as an air-born unloaded vessel, that can achieve twice the speed with a relative power; some trimaran configurations use the outlying hulls to enhance stability and allow for shallow draft, examples include the experimental ship RV Triton and the Independence class of littoral combat ships. Some multihulls with four or five hulls have been proposed. A Swiss entrepreneur is attempting to raise €25 million to build a sail-driven quadrimaran that would use solar power to scoop plastic from the ocean. A French manufacturer, Tera-4, produces motor quadrimarans which use aerodynamic lift between the four hulls to promote planing and reduce power consumption.
Design concepts for vessels with two pair of outriggers have been referred to as pentamarans. The design concept comprises a long hull that cuts through waves; the outriggers provide the stability that such a narrow hull needs. While the aft sponsons act as trimaran sponsons do, the front sponsons do not touch the water normally. BMT Group, a shipbuilding and engineering company in the UK, has proposed a fast cargo ship and a yacht using this kind of hull. Multihull designs may have hull beams; this arrangement allows good wave-piercing, while keeping a buoyant hydrodynamic hull beneath the waterplane. In a catamaran configuration this is called a small waterplane area twin hull, or SWATH. While SWATHs are stable in rough seas, they have the drawbacks, compared with other catamarans, of having a deeper draft, being more sensitive to loading, requiring more
On boats and ships, the keel is either of two parts: a structural element that sometimes resembles a fin and protrudes below a boat along the central line, or a hydrodynamic element. These parts overlap; as the laying down of the keel is the initial step in the construction of a ship, in British and American shipbuilding traditions the construction is dated from this event. Only the ship's launching is considered more significant in its creation; the word can be used as a synecdoche to refer to a complete boat, such as a keelboat. The adjustable centerboard keel traces its roots to the medieval Chinese Song dynasty. Many Song Chinese junk ships had a ballasted and bilge keel that consisted of wooden beams bound together with iron hoops. Maritime technology and the technological know-how allowed Song dynasty ships to be used in naval warfare between the Southern Song Dynasty, the Jin dynasty, the Mongols. A structural keel is the bottom-most structural member; the keel runs from the bow to the stern.
The keel is the first part of a ship's hull to be constructed, laying the keel, or placing the keel in the cradle in which the ship will be built may mark the start time of its construction. Large, modern ships are now built in a series of pre-fabricated, complete hull sections rather than being built around a single keel, so shipbuilding process commences with cutting the first sheet of steel; the most common type of keel is the "flat plate keel", this is fitted in the majority of ocean-going ships and other vessels. A form of keel found on smaller vessels is the "bar keel", which may be fitted in trawlers 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 inevitably of the flat plate type, bar keels being associated with open floors, where the plate keel may be fitted. Duct keels are provided in the bottom of some vessels.
These run from the forward engine room bulkhead to the collision bulkhead and are utilized to carry the double bottom piping. The piping is accessible when cargo is loaded; the keel surface on the bottom of the hull gives the ship greater directional stability. In non-sailing hulls, the keel helps the hull to move forward, rather than slipping to the side. In traditional boat building, this is provided by the structural keel, which projects from the bottom of the hull along most or all of its length. In modern construction, the bar keel or flat-plate keel performs the same function. There are many types of fixed keels, including full keels, long keels, fin keels, winged keels, bulb keels, bilge keels among other designs. Deep-draft ships will have a flat bottom and employ only bilge keels, both to aid directional control and to damp rolling motions In sailboats, keels use the forward motion of the boat to generate lift to counteract the leeward force of the wind; the rudimentary purpose of the keel is to convert the sideways motion of the wind when it is abeam into forward motion.
A secondary purpose of the keel is to provide ballast. Keels are different from centreboards and other types of foils in that keels are made of heavy materials to provide ballast to stabilize the boat. Keels may be fixed, or non-movable. Retracting keels may pivot or slide upwards to retract, are retracted with a winch due to the weight of the ballast. Since the keel provides far more stability when lowered than when retracted, the amount of sail carried is reduced when sailing with the keel retracted. Types of non-fixed keels include canting keels. Canting keels can be found on racing yachts, such as those competing in the Volvo Ocean Race, they provide more righting moment as the keel moves out to the windward-side of the boat while using less weight. The horizontal distance from the weight to the pivot is increased, which generates a larger righting moment; 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.
Carina is the origin of the term careen. An example of this use is Careening Cove, a suburb of Sydney, where careening was carried out in early colonial days. Coin ceremony Kelson False keel Daggerboard Leeboard Bilgeboard Bruce foil Keelhauling – an archaic maritime punishment Rousmaniere, The Annapolis Book of Seamanship, Simon & Schuster, 1999 Chapman Book of Piloting, Hearst Corporation, 1999 Herreshoff, The Sailor’s Handbook, Little Brown and Company Seidman, The Complete Sailor, International Marine, 1995 Jobson, Sailing Fundamentals, Simon & Schuster, 1987
Planing is the mode of operation for a waterborne craft in which its weight is predominantly supported by hydrodynamic lift, rather than hydrostatic lift. Many forms of marine transport make use of planing, including fast ferries, racing boats, flying boats, seaplanes. Most surfboards are semi-planing hulls. Beyond planing, fast vessel designs have seen a transition to hydrofoil designs; the earliest documented planing sailboat was a proa built in 1898 by Commodore Ralph Munroe. It was capable of speeds of more than twice the hull speed. Planing a sailing dinghy was first popularised by Uffa Fox in Britain. In 1928 Fox introduced planing to the racing world in Avenger; that year he gained 52 first places, 2 seconds, 3 third places out of 57 race starts. This performance was noticed by other designers who developed them. Over the years many dinghies have acquired the ability to plane. Advances in building materials have allowed for lighter boats that will plane faster and in lighter air. There are now many high-performance dinghies.
When it is at rest, a vessel's weight is borne by the buoyant force. At low speeds every hull acts as a displacement hull, meaning that the buoyant force is responsible for supporting the craft; as speed increases, hydrodynamic lift increases as well. In contrast, the buoyant force decreases as the hull lifts out of the water, decreasing the displaced volume. At some speed, lift becomes the predominant upward force on the hull and the vessel is planing. A simple model of this effect is a solid slab of material, heavier than water but is shaped and oriented to have a positive angle of attack. At rest, the slab will sink. However, if the slab is kept in the same orientation and pulled horizontally through the water, it will force the incoming water downward; this results in a reactionary force upward on the slab. At a high enough speed, this reactionary force is larger than the force of gravity and the slab will stay afloat. In this way, the horizontal force is converted into a vertical force upwards.
The concept of planing is interpreted as analogous with aerodynamic lift, but in reality the acting forces are different. Although any hull will plane if enough power is provided and enough speed is attained, a hull designed for operation in the planing realm is sometimes distinguished by a flat run aft. In other words, in side view, the bottom is less a straight line towards the stern. In contrast, in a displacement, or non-planing hull, the bottom is curved in side view all the way from bow to stern, in order to minimize wave drag. In front view, the sections in the aft area may be straight, as in a racing hydroplane, to maximize planing forces and speed, but for practical reasons of stability and comfortable ride are V-shaped in boats intended for offshore use. To plane to initiate planing, the power-to-weight ratio must be high, since the planing mode of operation involves moving the hull at speeds higher than its natural hull speed. All boat designs for planing benefit from minimised weight.
Planing sailing boats need powerboats need a high-power engine. Steps and chine ridges may be incorporated into the design to encourage both ease of planing and stability. Most surfboards, although unpowered, are semi-planing hulls, they utilize the push of the waveform more or less in combination with gravity and specific angles of attack for the airfoil to maximise propulsive force and reduce the net downforce and thus achieve planing lift. Planing may be achieved in most sailing dinghies. In light to moderate conditions, planing is best initiated by a combination of the following. Maximise power: sail on a reach or broad reach to begin. Minimise surface-induced drag: raise the centreboard or daggerboard about half way Maintain power: when a gust hits, bear away and ease the sheets As a gust begins to pass, steer to windward to keep the apparent wind forward Maintain flat form of immersed sections of hull: keep the hull level side-to-side, trapeze if necessary Move your weight aft to lift the bow Maintain power if necessary: flick or pump the sails Seek optimal form and speed of immersed hull: if there are waves, surf down them to initiate planing.
Hydroplane Dinghy racing Dinghy sailing Windsurfing Videos of planing sailboards from the UK Windsurfing Association
Phoenicia was a thalassocratic, ancient Semitic-speaking Mediterranean civilization that originated in the Levant Lebanon, in the west of the Fertile Crescent. Scholars agree that it was centered on the coastal areas of Lebanon and included northern Israel, southern Syria reaching as far north as Arwad, but there is some dispute as to how far south it went, the furthest suggested area being Ashkelon, its colonies reached the Western Mediterranean, such as Cádiz in Spain and most notably Carthage in North Africa, the Atlantic Ocean. The civilization spread across the Mediterranean between 1500 BC and 300 BC. Phoenicia is an ancient Greek term used to refer to the major export of the region, cloth dyed Tyrian purple from the Murex mollusc, referred to the major Canaanite port towns, their civilization was organized in city-states, similar to those of ancient Greece, centered in modern Lebanon, of which the most notable cities were Tyre, Arwad, Berytus and Carthage. Each city-state was a politically independent unit, it is uncertain to what extent the Phoenicians viewed themselves as a single nationality.
In terms of archaeology, language and religion there was little to set the Phoenicians apart as markedly different from other residents of the Levant, such as their close relatives and neighbors, the Israelites. Around 1050 BC, a Phoenician alphabet was used for the writing of Phoenician, it became one of the most used writing systems, spread by Phoenician merchants across the Mediterranean world, where it evolved and was assimilated by many other cultures, including the Roman alphabet used by Western civilization today. The name Phoenicians, like Latin Poenī, comes from Greek Φοίνικες; the word φοῖνιξ phoînix meant variably "Phoenician person", "Tyrian purple, crimson" or "date palm" and is attested with all three meanings in Homer. The word may be derived from φοινός phoinós "blood-red", itself related to φόνος phónos "murder", it is difficult to ascertain which meaning came first, but it is understandable how Greeks may have associated the crimson or purple color of dates and dye with the merchants who traded both products.
Robert S. P. Beekes has suggested a pre-Greek origin of the ethnonym; the oldest attested form of the word in Greek may be the Mycenaean po-ni-ki-jo, po-ni-ki borrowed from Ancient Egyptian: fnḫw, although this derivation is disputed. The folk etymological association of Φοινίκη with φοῖνιξ mirrors that in Akkadian, which tied kinaḫni, kinaḫḫi "Canaan" to kinaḫḫu "red-dyed wool"; the land was natively known as its people as the knʿny. In the Amarna letters of the 14th century BC, people from the region called themselves Kenaani or Kinaani, in modern English understood as/equivalent to Canaanite. Much in the sixth century BC, Hecataeus of Miletus writes that Phoenicia was called χνα khna, a name that Philo of Byblos adopted into his mythology as his eponym for the Phoenicians: "Khna, afterwards called Phoinix"; the ethnonym survived in North Africa until the fourth century AD. Herodotus's account refers to the myths of Europa. According to the Persians best informed in history, the Phoenicians began the quarrel.
These people, who had dwelt on the shores of the Erythraean Sea, having migrated to the Mediterranean and settled in the parts which they now inhabit, began at once, they say, to adventure on long voyages, freighting their vessels with the wares of Egypt and Assyria... The Greek historian Strabo believed. Herodotus believed that the homeland of the Phoenicians was Bahrain; this theory was accepted by the 19th-century German classicist Arnold Heeren who said that: "In the Greek geographers, for instance, we read of two islands, named Tyrus or Tylos, Aradus, which boasted that they were the mother country of the Phoenicians, exhibited relics of Phoenician temples." The people of Tyre in South Lebanon in particular have long maintained Persian Gulf origins, the similarity in the words "Tylos" and "Tyre" has been commented upon. The Dilmun civilization thrived in Bahrain during the period 2200–1600 BC, as shown by excavations of settlements and Dilmun burial mounds. However, some claim there is little evidence of occupation at all in Bahrain during the time when such migration had taken place.
Canaanite culture developed in situ from the earlier Ghassulian chalcolithic culture. Ghassulian itself developed from the Circum-Arabian Nomadic Pastoral Complex, which in turn developed from a fusion of their ancestral Natufian and Harifian cultures with Pre-Pottery Neolithic B farming cultures, practicing the domestication of animals, during the 6200 BC climatic crisis which led to the Neolithic Revolution in the Levant. Byblos is attested as an archaeological site from the Early Bronze Age; the Late Bronze Age state of Ugarit is considered quintessentially Canaanite archaeologically though the Ugaritic language does not belong to the Canaanite languages proper. The Canaanite-Phoenician alphabet consists of all consonants. Starting around 1050 BC, this script was used for the writing of Phoenician, a Northern Semitic language, it is believed to be one of the ancestors of modern alphabets. B
Ballast is used in ships to provide moment to resist the lateral forces on the hull. Insufficiently ballasted boats tend to heel excessively in high winds. Too much heel may result in the boat/ship capsizing. If a sailing vessel should need to voyage without cargo ballast of little or no value would be loaded to keep the vessel upright; some or all of this ballast would be discarded when cargo was loaded. Ballast takes many forms; the simplest form of ballast used in small day sailers is so-called "live ballast", or the weight of the crew. By sitting on the windward side of the hull, the heeling moment must lift the weight of the crew. On more advanced racing boats, a wire harness called a trapeze is used to allow the crew to hang over the side of the hull without falling out. On larger modern vessels, the keel is made of or filled with a high density material, such as concrete, iron, or lead. By placing the weight as low as possible the maximum righting moment can be extracted from the given mass.
Traditional forms of ballast carried inside the hull were stones or sand. There are disadvantages to using high-density ballast; the first is the increased mass of the boat. A heavier boat is more difficult to put on a trailer and tow behind an automobile. Secondly, since the ballast needs to be as low as possible, it is placed into a centerboard or retracting keel, requiring a heavy-duty crank to lift the massive foil; the simplest solution is to use a fixed ballasted keel, but that makes the boat nearly incapable of sailing in shallow water, more difficult to handle when out of the water. While prohibited by most class racing rules, some cutting-edge boats use a bulb of ballast on a long, thin keel that can tilt from side to side to create a canting keel; this lets the ballast be placed on the windward side, providing a far greater righting moment with a lower angle of heel. Tilting the keel, however reduces its lift, so canting keels are combined with a retractable centerboard or daggerboard, deployed when the keel is tilted, retracted when the keel is returned to the vertical.
Some canting keels are designed so that when extended to either side they have an angle of attack of about 5° allowing the hydrofoil effect of the blade to lift the boat up and reduce wetted surface area for an increase in boat speed. A common type of ballast for small boats that avoids many of the problems of high-density ballast is water ballast. While it seems counter-intuitive that placing water in the hull would add any stability, adding water ballast below the vertical center of gravity increases stability; the water ballast does not need to be lifted above the waterline to affect stability, as any material having greater bulk density than air will have an effect on the centre of gravity. It is the relationship between centre of gravity and centre of buoyancy that dictates the righting moment; the advantage of water ballast is that the tanks can be emptied, reducing draft or the weight of the boat and water added back in after the boat is launched or cargo unloaded. Pumps can be used to empty the leeward ballast tank and fill the windward tank as the boat tacks, the quantity of ballast can be varied to keep the boat at the optimum angle of heel.
On empty cargo vessels water is added to ballast tanks to increase propeller immersion, to improve steering, to control trim and draft. A disadvantage of water ballast is that water is not dense and therefore the tanks required take up more space than other forms of ballast; some manufacturers offer flexible ballast bags that are mounted outboard of the hull on both sides, pumps that use the boat's speed through the water for power. When under way, the pump can be used to fill the windward side, while the lee side is allowed to drain; this system, while not attractive, does allow significant gains in righting force with no modifications to the hull. A trick used on boats with water ballast is to link port and starboard tanks with a valved pipe; when preparing to tack, the valve is opened, water in the windward tank, higher, is allowed to flow to the lee side, the sheet is let off to keep the boat from heeling too far. Once as much water as possible has been transferred to the lee side, the boat is brought about and the sail sheeted in, lifting the newly full windward tank.
A simple hand pump can be used to move any remaining water from the lee to the windward tank. Cruise ships, large tankers, bulk cargo carriers use a tremendous amount of ballast water, taken on in the coastal waters in one region after ships discharge wastewater or unload cargo, discharged at the next port of call, wherever more cargo is loaded. Ballast water discharge contains a variety of biological materials, including plants, animals and other microorganisms; these materials include non-native, exotic species that can cause extensive ecological and economic damage to aquatic ecosystems. Ballast water discharges are believed to be the leading source of invasive species in U. S. marine waters, thus posing public health and environmental risks, as well as significant economic cost to indust
A sailboat or sailing boat is a boat propelled or by sails smaller than a sailing ship. Distinctions in what constitutes a sailing boat and ship vary by maritime culture. Although sailboat terminology has varied across history, many terms have specific meanings in the context of modern yachting. A great number of sailboat-types may be distinguished by size, hull configuration, keel type, purpose and configuration of masts, sail plan. Popular monohull designs include: The cutter is similar to a sloop with a single mast and mainsail, but carries the mast further aft to allow for a jib and staysail to be attached to the head stay and inner forestay, respectively. Once a common racing configuration, today it gives versatility to cruising boats in allowing a small staysail to be flown from the inner stay in high winds. A catboat does not carry a jib. Most modern designs have the mainsail. A dinghy is a type of small open sailboat used for recreation, sail training, tending a larger vessel, they are popular in youth sailing programs for their short LOA, simple operation and minimal maintenance.
They have three sails: the mainsail and spinnaker. Ketches are similar to a sloop, but there is a second shorter mast astern of the mainmast, but forward of the rudder post; the second mast is called the mizzen mast and the sail is called the mizzen sail. A ketch can be Cutter-rigged with two head sails. A schooner has a mainmast taller than its foremast, distinguishing it from a yawl. A schooner can have more than two masts, with the foremast always lower than the foremost main. Traditional topsail schooners have topmasts allowing triangular topsails sails to be flown above their gaff sails; the most common modern sailboat is the sloop, which features one mast and two sails a Bermuda rigged main, a headsail. This simple configuration is efficient for sailing into the wind. A fractional rigged sloop has its forestay attached at a point below the top of the mast, allowing the mainsail to be flattened to improve performance by raking the upper part of the mast aft by tensioning the backstay. A smaller headsail is easier for a short-handed crew to manage.
A yawl is similar to a ketch, with a shorter mizzen mast carried astern the rudderpost more for balancing the helm than propulsion. Traditional sailboats are monohulls. Monohull boats rely on ballast for stability and are displacement hulls; this stabilizing ballast can, in boats designed for racing, be as much as 50% of the weight of the boat, but is around 30%. It creates two problems. Secondly, unless it has been built with buoyant foam or air tanks, if a monohull fills with water, it will sink. Multihulls rely on the geometry and the broad stance of their multiple hulls for their stability, eschewing any form of ballast. Multihulls are designed to be as light-weight as possible while still maintaining structural integrity, they are built with foam-filled flotation chambers and many modern commercial trimarans are rated as unsinkable, meaning that, should every crew compartment be filled with water, the hull itself has sufficient buoyancy to remain afloat. This absence of ballast results in performance gains in terms of acceleration, top speed, maneuverability.
The lack of ballast makes it much easier to get a multihull on plane, reducing its wetted surface area and thus its drag. The absence of drag improves wind precision. Compared to a monohull, acceleration to top speed is near-instantaneous. Reduced overall weight means a reduced draft, with a much reduced underwater profile. This, in turn, results directly in reduced wetted surface area and drag.. Without a ballast keel, multihulls can go in shallow waters. There are trade offs, however, in multihull design. A well designed ballasted boat can recover from a capsize from turning over completely. Righting a multihull that has gotten upside down is difficult in any case and impossible without help unless the boat is small or carries special equipment for the purpose. Multihulls prove more difficult to tack, since the reduced weight leads directly to reduced momentum, causing multihulls to more lose speed when headed into the wind. Structural integrity is much easier to achieve in a one piece monohull than in a two or three piece multihull whose connecting structure must be substantial and well connected to the hulls.
All these hull types may be manufactured as, or outfitted with, hydrofoils. All vessels have a keel, it is the backbone of the hull. In traditional construction, it is the structure upon. Modern monocoque designs include a virtual keel. Multihulls have keels. On a sailboat, the word "keel" is used to refer to the area, added to the hull to improve its lateral plane; the lateral plane is what allows sailing towards the wind. This can be a part of the hull. Most monohulls larger. Depending on the design of the boat, ballast may be 20 to 50 percent of the displacement; the ballast is integrated into their keels as large masses of lead or cast iron. This gets it as low as possible to improve its effectiveness. External keels are cast in the shape of the keel. A monohull's keel is made effective by a combination of weight and length. Most modern monohull boats ha