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89-403: When a ship's crew has died or abandoned the ship, and the ship has remained adrift but unsunk, they are instead referred to as ghost ships . Historic wrecks are attractive to maritime archaeologists because they preserve historical information: for example, studying the wreck of Mary Rose revealed information about seafaring, warfare, and life in the 16th century. Military wrecks, caused by

178-428: A construction material , for making tools and weapons , furniture and paper . More recently it emerged as a feedstock for the production of purified cellulose and its derivatives, such as cellophane and cellulose acetate . As of 2020, the growing stock of forests worldwide was about 557 billion cubic meters. As an abundant, carbon-neutral renewable resource, woody materials have been of intense interest as

267-733: A glacial-fed lake, Arctic waters, the Great Lakes , etc.) slows the degradation of organic ship materials. Decay, corrosion and marine encrustation are inhibited or largely absent in cold waters. Many modern shipwrecks contribute to marine pollution , mainly as sources of significant oil spills . A 2005 survey of shipwrecks since 1890 found that over 8,500 of the submerged wrecks may still contain oil. Oil spills can have devastating effects on marine and coastal environments as well as fisheries. In addition to being toxic to marine life, polycyclic aromatic hydrocarbons (PAHs), found in crude oil , are very difficult to clean up, and last for years in

356-572: A blanket ban on all diving; for other wrecks divers may visit provided they do not touch, interfere with or penetrate the wreck. In the United States, shipwrecks in state waters are regulated by the Abandoned Shipwrecks Act of 1987. This act is much more lenient in allowing more open access to the shipwrecks. Following the beaching of MSC Napoli , as a result of severe damage incurred during European storm Kyrill , there

445-445: A certain age, the original owner may have lost all claim to the cargo. Anyone who finds the wreck can then file a salvage claim on it and place a lien on the vessel, and subsequently mount a salvage operation (see Finders, keepers ). The State of North Carolina questionably claims "all photographs, video recordings, or other documentary materials of a derelict vessel or shipwreck or its contents, relics, artifacts, or historic materials in

534-776: A greater or lesser degree in an Australian case and in a Norwegian case. The American courts have been inconsistent between states and at federal level. Under Danish law, all shipwrecks over 150 years old belong to the state if no owner can be found. In Spain, wrecks vest in the state if not salvaged within 3 years. In Finland, all property on board shipwrecks over 100 years old vests in the state. The British Protection of Wrecks Act , enacted to protect historic wrecks, controls access to wrecks such as Cattewater Wreck which can only be visited or investigated under licence. The British Protection of Military Remains Act 1986 also restricts access to wrecks which are sensitive as war graves . The Protection of Military Remains Act in some cases creates

623-401: A heavy piece of pine is compared with a lightweight piece it will be seen at once that the heavier one contains a larger proportion of latewood than the other, and is therefore showing more clearly demarcated growth rings. In white pines there is not much contrast between the different parts of the ring, and as a result the wood is very uniform in texture and is easy to work. In hard pines , on

712-405: A large log the sapwood, because of the time in the life of the tree when it was grown, may be inferior in hardness , strength , and toughness to equally sound heartwood from the same log. In a smaller tree, the reverse may be true. In species which show a distinct difference between heartwood and sapwood the natural color of heartwood is usually darker than that of the sapwood, and very frequently

801-400: A log is on the outside, it is more or less knotty near the middle. Consequently, the sapwood of an old tree, and particularly of a forest-grown tree, will be freer from knots than the inner heartwood. Since in most uses of wood, knots are defects that weaken the timber and interfere with its ease of working and other properties, it follows that a given piece of sapwood, because of its position in

890-589: A physical derelict found adrift with its crew missing or dead, like the Mary Celeste . The term is sometimes used for ships that have been decommissioned but not yet scrapped , as well as drifting boats that have been found after breaking loose of their ropes and being carried away by the wind or the waves. More recently, ships which travel with their mandated Automatic identification system turned off to avoid detection and monitoring, have also been referred to as ghost ships . Wood Wood

979-481: A pretty definite relation between the rate of growth of timber and its properties. This may be briefly summed up in the general statement that the more rapid the growth or the wider the rings of growth, the heavier, harder, stronger, and stiffer the wood. This, it must be remembered, applies only to ring-porous woods such as oak, ash, hickory, and others of the same group, and is, of course, subject to some exceptions and limitations. In ring-porous woods of good growth, it

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1068-460: A shipwreck) and adventurae maris (material still at sea), which are treated differently by some, but not all, legal systems. Wrecks are often considered separately from their cargo. For example, in the British case of Lusitania [1986] QB 384 it was accepted that the remains of the vessel itself were owned by the insurance underwriters who had paid out on the vessel as a total loss by virtue of

1157-444: A skirmish at sea, are studied to find details about the historic event; they reveal much about the battle that occurred. Discoveries of treasure ships , often from the period of European colonisation , which sank in remote locations leaving few living witnesses, such as Batavia , do occur as well. Some contemporary wrecks, such as the oil tanker Prestige or Erika , are of interest primarily because of their potential harm to

1246-636: A source of renewable energy. In 2008, approximately 3.97 billion cubic meters of wood were harvested. Dominant uses were for furniture and building construction. Wood is scientifically studied and researched through the discipline of wood science , which was initiated since the beginning of the 20th century. A 2011 discovery in the Canadian province of New Brunswick yielded the earliest known plants to have grown wood, approximately 395 to 400 million years ago . Wood can be dated by carbon dating and in some species by dendrochronology to determine when

1335-465: A source of weakness. In diffuse-porous woods the pores are evenly sized so that the water conducting capability is scattered throughout the growth ring instead of being collected in a band or row. Examples of this kind of wood are alder , basswood , birch , buckeye, maple, willow , and the Populus species such as aspen, cottonwood and poplar. Some species, such as walnut and cherry , are on

1424-784: A treasure almost three miles (16,000 ft; 4,800 m) deep. A U.S. federal court and a panel from the United States Court of Appeals for the Eleventh Circuit have upheld the Spanish claim to the contents of the ship Nuestra Señora de las Mercedes ; Spain took control of the treasure in February 2012. A very small number of coins and effects recovered from the ship were deposited in Gibraltar, because they showed clear signs coherent with an internal explosion on

1513-564: A tree is first formed as sapwood. The more leaves a tree bears and the more vigorous its growth, the larger the volume of sapwood required. Hence trees making rapid growth in the open have thicker sapwood for their size than trees of the same species growing in dense forests. Sometimes trees (of species that do form heartwood) grown in the open may become of considerable size, 30 cm (12 in) or more in diameter, before any heartwood begins to form, for example, in second growth hickory , or open-grown pines . No definite relation exists between

1602-423: A type of imperfection known as a knot. The dead branch may not be attached to the trunk wood except at its base and can drop out after the tree has been sawn into boards. Knots affect the technical properties of the wood, usually reducing tension strength, but may be exploited for visual effect. In a longitudinally sawn plank, a knot will appear as a roughly circular "solid" (usually darker) piece of wood around which

1691-492: A wooden object was created. People have used wood for thousands of years for many purposes, including as a fuel or as a construction material for making houses , tools , weapons , furniture , packaging , artworks , and paper . Known constructions using wood date back ten thousand years. Buildings like the longhouses in Neolithic Europe were made primarily of wood. Recent use of wood has been enhanced by

1780-717: Is Queen Anne's Revenge which is undergoing archaeological recovery by the North Carolina Department of Cultural Resources near Beaufort Inlet, NC. An important international convention aiming at the protection of underwater cultural heritage (including shipwrecks) is the Convention on the Protection of the Underwater Cultural Heritage. The 2001 UNESCO Convention on the Protection of the Underwater Cultural Heritage represents

1869-437: Is a season check in the knot, as is often the case, it will offer little resistance to this tensile stress. Small knots may be located along the neutral plane of a beam and increase the strength by preventing longitudinal shearing . Knots in a board or plank are least injurious when they extend through it at right angles to its broadest surface. Knots which occur near the ends of a beam do not weaken it. Sound knots which occur in

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1958-401: Is a structural tissue/material found as xylem in the stems and roots of trees and other woody plants . It is an organic material  – a natural composite of cellulosic fibers that are strong in tension and embedded in a matrix of lignin that resists compression. Wood is sometimes defined as only the secondary xylem in the stems of trees, or more broadly to include

2047-456: Is also greatly increased in strength thereby. Since the latewood of a growth ring is usually darker in color than the earlywood, this fact may be used in visually judging the density, and therefore the hardness and strength of the material. This is particularly the case with coniferous woods. In ring-porous woods the vessels of the early wood often appear on a finished surface as darker than the denser latewood, though on cross sections of heartwood

2136-428: Is an important consideration. The weakening effect is much more serious when timber is subjected to forces perpendicular to the grain and/or tension than when under load along the grain and/or compression . The extent to which knots affect the strength of a beam depends upon their position, size, number, and condition. A knot on the upper side is compressed, while one on the lower side is subjected to tension. If there

2225-491: Is an international treaty aimed exclusively at the protection of underwater cultural heritage and the facilitation of international cooperation in this regard. It does not change sovereignty rights of States or regulate the ownership of wrecks or submerged ruins. In 2011, the most valuable cargo of a sunken shipwreck was identified near the western edge of the Celtic Sea . This World War II era sinking of Gairsoppa led to

2314-422: Is dark colored and firm, and consists mostly of thick-walled fibers which form one-half or more of the wood. In inferior oak, this latewood is much reduced both in quantity and quality. Such variation is very largely the result of rate of growth. Wide-ringed wood is often called "second-growth", because the growth of the young timber in open stands after the old trees have been removed is more rapid than in trees in

2403-560: Is difficult to control completely, especially when using mass-produced kiln-dried timber stocks. Heartwood (or duramen ) is wood that as a result of a naturally occurring chemical transformation has become more resistant to decay. Heartwood formation is a genetically programmed process that occurs spontaneously. Some uncertainty exists as to whether the wood dies during heartwood formation, as it can still chemically react to decay organisms, but only once. The term heartwood derives solely from its position and not from any vital importance to

2492-399: Is in the walls, not the cavities. Hence the greater the proportion of latewood, the greater the density and strength. In choosing a piece of pine where strength or stiffness is the important consideration, the principal thing to observe is the comparative amounts of earlywood and latewood. The width of ring is not nearly so important as the proportion and nature of the latewood in the ring. If

2581-486: Is known as secondary growth ; it is the result of cell division in the vascular cambium , a lateral meristem, and subsequent expansion of the new cells. These cells then go on to form thickened secondary cell walls, composed mainly of cellulose , hemicellulose and lignin . Where the differences between the seasons are distinct, e.g. New Zealand , growth can occur in a discrete annual or seasonal pattern, leading to growth rings ; these can usually be most clearly seen on

2670-431: Is laid down on the outside of the wood previously formed, it follows that unless a tree materially increases its production of wood from year to year, the rings must necessarily become thinner as the trunk gets wider. As a tree reaches maturity its crown becomes more open and the annual wood production is lessened, thereby reducing still more the width of the growth rings. In the case of forest-grown trees so much depends upon

2759-470: Is more complex. The water conducting capability is mostly taken care of by vessels : in some cases (oak, chestnut, ash) these are quite large and distinct, in others ( buckeye , poplar , willow ) too small to be seen without a hand lens. In discussing such woods it is customary to divide them into two large classes, ring-porous and diffuse-porous . In ring-porous species, such as ash, black locust, catalpa , chestnut, elm , hickory, mulberry , and oak,

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2848-552: Is that any such finds and recovery must be reported within 28 days to the Receiver of Wreck . Failure to do so is an offence under the Merchant Shipping Act and can result in a criminal record for theft by finding . After several days, the police and Receiver of Wreck, in conjunction with the landowner and the contracted salvors , established a cordon to prevent access to the beach. A similar situation occurred after

2937-404: Is the historical value of the shipwreck that counts as well as any slight piece of information or evidence that is acquired. Exposed wooden components decay quickly. Often the only wooden parts of ships that remain after a century are those that were buried in silt or sand soon after the sinking. An example of this is Mary Rose . Steel and iron , depending on their thickness, may retain

3026-431: Is the rule. Some others never form heartwood. Heartwood is often visually distinct from the living sapwood and can be distinguished in a cross-section where the boundary will tend to follow the growth rings. For example, it is sometimes much darker. Other processes such as decay or insect invasion can also discolor wood, even in woody plants that do not form heartwood, which may lead to confusion. Sapwood (or alburnum )

3115-413: Is the younger, outermost wood; in the growing tree it is living wood, and its principal functions are to conduct water from the roots to the leaves and to store up and give back according to the season the reserves prepared in the leaves. By the time they become competent to conduct water, all xylem tracheids and vessels have lost their cytoplasm and the cells are therefore functionally dead. All wood in

3204-400: Is then known as the latewood or summerwood. There are major differences, depending on the kind of wood. If a tree grows all its life in the open and the conditions of soil and site remain unchanged, it will make its most rapid growth in youth, and gradually decline. The annual rings of growth are for many years quite wide, but later they become narrower and narrower. Since each succeeding ring

3293-461: Is usually the latewood in which the thick-walled, strength-giving fibers are most abundant. As the breadth of ring diminishes, this latewood is reduced so that very slow growth produces comparatively light, porous wood composed of thin-walled vessels and wood parenchyma. In good oak, these large vessels of the earlywood occupy from six to ten percent of the volume of the log, while in inferior material they may make up 25% or more. The latewood of good oak

3382-550: The Antikythera Mechanism , is perhaps the earliest example of what would be known as today as an analog computer , and the technology it encompasses predates any other recorded description by hundreds or thousands of years. Ghost ship A ghost ship , also known as a phantom ship , is a vessel with no living crew aboard; it may be a fictional ghostly vessel, such as the Flying Dutchman , or

3471-511: The Great Lakes of North America, have remained intact with little degradation. In some sea areas, most notably in Gulf of Bothnia and Gulf of Finland , salinity is very low, and centuries-old wrecks have been preserved in reasonable condition. However, bacteria found in fresh water cause the wood on ships to rot more quickly than in seawater unless it is deprived of oxygen. Two shipwrecks, USS  Hamilton and USS  Scourge , have been at

3560-401: The grain of the rest of the wood "flows" (parts and rejoins). Within a knot, the direction of the wood (grain direction) is up to 90 degrees different from the grain direction of the regular wood. In the tree a knot is either the base of a side branch or a dormant bud. A knot (when the base of a side branch) is conical in shape (hence the roughly circular cross-section) with the inner tip at

3649-429: The resin which increases the strength when dry. Such resin-saturated heartwood is called "fat lighter". Structures built of fat lighter are almost impervious to rot and termites , and very flammable. Tree stumps of old longleaf pines are often dug, split into small pieces and sold as kindling for fires. Stumps thus dug may actually remain a century or more since being cut. Spruce impregnated with crude resin and dried

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3738-608: The sediment and marine environment. Shipwreck pollution may also originate with a ship's cargo or munitions, such as unexploded ordnance or chemical weapons canisters. German trawler V 1302 John Mahn , sunk in the North Sea in 1942, has multiple unexploded depth charges on board which render the wreck hazardous. Samples taken from the wreck and nearby sediment show the presence of heavy metals like nickel and copper, polycyclic aromatic hydrocarbons , arsenic and explosive compounds into surrounding waters, which have changed

3827-491: The German government, although Nazi Germany (the government at the time) is long-defunct. Many military wrecks are also protected by virtue of being war graves . However, many legal systems allow the rights of salvors to override the rights of the original owners of a wreck or its cargo. As a general rule, non-historic civilian shipwrecks are considered fair game for salvage. Under international maritime law , for shipwrecks of

3916-433: The addition of steel and bronze into construction. The year-to-year variation in tree-ring widths and isotopic abundances gives clues to the prevailing climate at the time a tree was cut. Wood, in the strict sense, is yielded by trees , which increase in diameter by the formation, between the existing wood and the inner bark , of new woody layers which envelop the entire stem, living branches, and roots. This process

4005-418: The annual rings of growth and the amount of sapwood. Within the same species the cross-sectional area of the sapwood is very roughly proportional to the size of the crown of the tree. If the rings are narrow, more of them are required than where they are wide. As the tree gets larger, the sapwood must necessarily become thinner or increase materially in volume. Sapwood is relatively thicker in the upper portion of

4094-517: The artifacts on and around the wreck at Pickles Reef and the over-lapping wrecks at the Molasses Reef Wreck , or contemporary pollution in bodies of water, that severely affect shipwrecks by changing the chemical structures, or further damaging what is left of a specific ship. Despite these challenges, if the information retrieved does not appear to be sufficient, or a poor preservation is achieved, authors like J.A. Parker claim that it

4183-449: The border between the two classes, forming an intermediate group. In temperate softwoods, there often is a marked difference between latewood and earlywood. The latewood will be denser than that formed early in the season. When examined under a microscope, the cells of dense latewood are seen to be very thick-walled and with very small cell cavities, while those formed first in the season have thin walls and large cell cavities. The strength

4272-512: The bottom of Lake Ontario since they sunk during a violent storm on August 8, 1813, during the War of 1812 . They are in "remarkably good" condition. Wrecks typically decay rapidly when in seawater . There are several reasons for this: An important factor in the condition of the wreck is the level of destruction at the time of the loss or shortly afterwards due to the nature of the loss, salvage or later demolition. Examples of severe destruction at

4361-547: The catastrophic Titanic , MV Doña Paz , Britannic , Lusitania , Estonia , Empress of Ireland , Andrea Doria , Endurance or Costa Concordia . There are also thousands of wrecks that were not lost at sea but have been abandoned or sunk. These abandoned, or derelict ships are typically smaller craft, such as fishing vessels. They may pose a hazard to navigation and may be removed by port authorities . Poor design, improperly stowed cargo , navigation and other human errors leading to collisions (with another ship,

4450-458: The cell walls are composed of micro-fibrils of cellulose (40–50%) and hemicellulose (15–25%) impregnated with lignin (15–30%). In coniferous or softwood species the wood cells are mostly of one kind, tracheids , and as a result the material is much more uniform in structure than that of most hardwoods . There are no vessels ("pores") in coniferous wood such as one sees so prominently in oak and ash, for example. The structure of hardwoods

4539-435: The central portion one-fourth the height of the beam from either edge are not serious defects. Knots do not necessarily influence the stiffness of structural timber; this will depend on the size and location. Stiffness and elastic strength are more dependent upon the sound wood than upon localized defects. The breaking strength is very susceptible to defects. Sound knots do not weaken wood when subject to compression parallel to

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4628-445: The competition of the trees in their struggle for light and nourishment that periods of rapid and slow growth may alternate. Some trees, such as southern oaks , maintain the same width of ring for hundreds of years. On the whole, as a tree gets larger in diameter the width of the growth rings decreases. As a tree grows, lower branches often die, and their bases may become overgrown and enclosed by subsequent layers of trunk wood, forming

4717-433: The contrast is conspicuous (see section of yew log above). This is produced by deposits in the heartwood of chemical substances, so that a dramatic color variation does not imply a significant difference in the mechanical properties of heartwood and sapwood, although there may be a marked biochemical difference between the two. Some experiments on very resinous longleaf pine specimens indicate an increase in strength, due to

4806-588: The custody of any agency of North Carolina government or its subdivisions" to be its property. Some countries assert claims to all wrecks within their territorial waters, irrespective of the interest of the original owner or the salvor. Some legal systems regard a wreck and its cargo to be abandoned if no attempt is made to salvage them within a certain period of time. English law has usually resisted this notion (encouraged by an extremely large maritime insurance industry, which asserts claims in respect of shipwrecks which it has paid claims on), but it has been accepted to

4895-448: The damage of marine creatures that create a home out of them, primarily octopuses and crustaceans. These creatures affect the primary state because they move, or break, any parts of the shipwreck that are in their way, thereby affecting the original condition of amphorae , for example, or any other hollow places. Finally, in addition to the slight or severe destruction marine animals can create, there are also "external" contaminants, such as

4984-415: The end of a log, but are also visible on the other surfaces. If the distinctiveness between seasons is annual (as is the case in equatorial regions, e.g. Singapore ), these growth rings are referred to as annual rings. Where there is little seasonal difference growth rings are likely to be indistinct or absent. If the bark of the tree has been removed in a particular area, the rings will likely be deformed as

5073-421: The environment. Other contemporary wrecks are scuttled in order to spur reef growth, such as Adolphus Busch and Ocean Freeze . Many contemporary and historic wrecks, such as Thistlegorm , are of interest to recreational divers that dive to shipwrecks because they are interesting to explore, provide large habitats for many types of marine life, and have an interesting history. Well-known shipwrecks include

5162-403: The exact mechanisms determining the formation of earlywood and latewood. Several factors may be involved. In conifers, at least, rate of growth alone does not determine the proportion of the two portions of the ring, for in some cases the wood of slow growth is very hard and heavy, while in others the opposite is true. The quality of the site where the tree grows undoubtedly affects the character of

5251-505: The grain. In some decorative applications, wood with knots may be desirable to add visual interest. In applications where wood is painted , such as skirting boards, fascia boards, door frames and furniture, resins present in the timber may continue to 'bleed' through to the surface of a knot for months or even years after manufacture and show as a yellow or brownish stain. A knot primer paint or solution (knotting), correctly applied during preparation, may do much to reduce this problem but it

5340-412: The greater the water content, the greater its softening effect. The moisture in wood can be measured by several different moisture meters . Drying produces a decided increase in the strength of wood, particularly in small specimens. An extreme example is the case of a completely dry spruce block 5 cm in section, which will sustain a permanent load four times as great as a green (undried) block of

5429-434: The international community's response to the increasing looting and destruction of underwater cultural heritage. It forms part of a group of UNESCO standard setting instruments regarding the domain of cultural heritage, encompassing seven conventions adopted by UNESCO Member States, which constitute a coherent and complementary body guaranteeing a complete protection of all forms of cultural heritage. The UNESCO 2001 Convention

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5518-407: The larger vessels or pores (as cross sections of vessels are called) are localized in the part of the growth ring formed in spring, thus forming a region of more or less open and porous tissue. The rest of the ring, produced in summer, is made up of smaller vessels and a much greater proportion of wood fibers. These fibers are the elements which give strength and toughness to wood, while the vessels are

5607-410: The law of subrogation (who subsequently sold their rights), but that the property aboard the wreck still belonged to its original owners or their heirs. Military wrecks, however, remain under the jurisdiction – and hence protection – of the government that lost the ship, or that government's successor. Hence, a German U-boat from World War II still technically belongs to

5696-449: The local microbial ecology. Iron and steel wrecks are subject to corrosion, which is most rapid in shallow sea water where the salinity induces galvanic corrosion, oxygen content is high and water movement replenishes the oxygen rapidly. In deeper water and in still water the corrosion rates can be greatly reduced. Corrosion rates of iron and steel are also reduced when concretions, solid layers of rust, or layers of marine organisms separate

5785-711: The metal from the ambient water, and encourage the development of a layer of relatively stable black oxide in the hypoxic layers. Ships that sink upright onto a sand bottom tend to settle into the sand to a similar level to that at which they would normally float at the surface. The thinner materials of the upper works tend to break up first, followed by the decks and deck beams, and the hull sides unsupported by bulkheads. The bow and stern may remain relatively intact for longer as they are usually more heavily constructed. Heavy machinery like boilers, engines, pumps, winches, propellers, propeller shafts, steering gear, anchors and other heavy fittings also last longer and can provide support to

5874-480: The moisture content of the air) retains 8–16% of the water in the cell walls, and none, or practically none, in the other forms. Even oven-dried wood retains a small percentage of moisture, but for all except chemical purposes, may be considered absolutely dry. The general effect of the water content upon the wood substance is to render it softer and more pliable. A similar effect occurs in the softening action of water on rawhide, paper, or cloth. Within certain limits,

5963-542: The other hand, the latewood is very dense and is deep-colored, presenting a very decided contrast to the soft, straw-colored earlywood. It is not only the proportion of latewood, but also its quality, that counts. In specimens that show a very large proportion of latewood it may be noticeably more porous and weigh considerably less than the latewood in pieces that contain less latewood. One can judge comparative density, and therefore to some extent strength, by visual inspection. No satisfactory explanation can as yet be given for

6052-404: The plant overgrows the scar. If there are differences within a growth ring, then the part of a growth ring nearest the center of the tree, and formed early in the growing season when growth is rapid, is usually composed of wider elements. It is usually lighter in color than that near the outer portion of the ring, and is known as earlywood or springwood. The outer portion formed later in the season

6141-605: The point in stem diameter at which the plant's vascular cambium was located when the branch formed as a bud. In grading lumber and structural timber , knots are classified according to their form, size, soundness, and the firmness with which they are held in place. This firmness is affected by, among other factors, the length of time for which the branch was dead while the attaching stem continued to grow. Knots materially affect cracking and warping, ease in working, and cleavability of timber. They are defects which weaken timber and lower its value for structural purposes where strength

6230-411: The properties of the wood. Certain rot-producing fungi impart to wood characteristic colors which thus become symptomatic of weakness. Ordinary sap-staining is due to fungal growth, but does not necessarily produce a weakening effect. Water occurs in living wood in three locations, namely: In heartwood it occurs only in the first and last forms. Wood that is thoroughly air-dried (in equilibrium with

6319-406: The remaining hull, or cause it to collapse more rapidly. Vessels that come to rest upside down on a yielding seabed can be relatively stable, although the upper decks usually collapse under the load and machinery and fittings fall. Wrecks that rest on their side tend to deteriorate quickly, as the loads are not what they were designed to support, and poorly supported hull sides give way fairly soon and

6408-468: The reverse is commonly true. Otherwise the color of wood is no indication of strength. Abnormal discoloration of wood often denotes a diseased condition, indicating unsoundness. The black check in western hemlock is the result of insect attacks. The reddish-brown streaks so common in hickory and certain other woods are mostly the result of injury by birds. The discoloration is merely an indication of an injury, and in all probability does not of itself affect

6497-453: The same size will. The greatest strength increase due to drying is in the ultimate crushing strength, and strength at elastic limit in endwise compression; these are followed by the modulus of rupture, and stress at elastic limit in cross-bending, while the modulus of elasticity is least affected. Wood is a heterogeneous , hygroscopic , cellular and anisotropic (or more specifically, orthotropic ) material. It consists of cells, and

6586-494: The same type of tissue elsewhere, such as in the roots of trees or shrubs. In a living tree, it performs a mechanical-support function, enabling woody plants to grow large or to stand up by themselves. It also conveys water and nutrients among the leaves , other growing tissues, and the roots. Wood may also refer to other plant materials with comparable properties, and to material engineered from wood, woodchips , or fibers . Wood has been used for thousands of years for fuel , as

6675-555: The ship and thus confirmed Spanish claims to the wreck being that of the Nuestra Señora de las Mercedes . They were not returned to Spain until 2013, when a court finally ordered Odyssey Marine to return the missing pieces. Archaeologist Valerios Stais discovered one of the most notable instruments of time keeping and prediction of celestial events off the coast of the Greek island Antikythera on May 17, 1902. The device, known as

6764-490: The ship's structure for decades. As corrosion takes place, sometimes helped by tides and weather, the structure collapses. Thick ferrous objects such as cannons , steam boilers or the pressure vessel of a submarine often survive well underwater in spite of corrosion. Propellers , condensers , hinges and port holes were often made from non-ferrous metals such as brass and phosphor bronze , which do not corrode easily. Shipwrecks in some freshwater lakes, such as

6853-407: The shoreline, an iceberg, etc.), bad weather, fire , and other causes can lead to accidental sinking. Intentional reasons for sinking a ship include: intending to form an artificial reef ; destruction due to warfare , piracy , mutiny or sabotage ; using the vessel for target practice ; or removing a menace to navigation. A ship can be also used as breakwater structure . Many factors determine

6942-402: The state of preservation of a wreck: The above - especially the stratification (silt/sand sediments piled up on the shipwrecks) and the damages caused by marine creatures - is better described as "stratification and contamination" of shipwrecks. The stratification not only creates another challenge for marine archaeology, but also a challenge to determine its primary state, i.e. the state that it

7031-409: The time of loss are: After the loss, the vessel's owners may attempt to salvage valuable parts of the ship and its cargo. This operation can cause further damage. Shipwrecks in shallow water near busy shipping lanes are often demolished or removed to reduce the danger to other vessels. On charts, some wreck symbols have a line under the symbol with a depth mark, which indicates the water depth above

7120-430: The tree, may well be stronger than a piece of heartwood from the same tree. Different pieces of wood cut from a large tree may differ decidedly, particularly if the tree is big and mature. In some trees, the wood laid on late in the life of a tree is softer, lighter, weaker, and more even textured than that produced earlier, but in other trees, the reverse applies. This may or may not correspond to heartwood and sapwood. In

7209-445: The tree. This is evidenced by the fact that a tree can thrive with its heart completely decayed. Some species begin to form heartwood very early in life, so having only a thin layer of live sapwood, while in others the change comes slowly. Thin sapwood is characteristic of such species as chestnut , black locust , mulberry , osage-orange , and sassafras , while in maple , ash , hickory , hackberry , beech , and pine, thick sapwood

7298-416: The trunk of a tree than near the base, because the age and the diameter of the upper sections are less. When a tree is very young it is covered with limbs almost, if not entirely, to the ground, but as it grows older some or all of them will eventually die and are either broken off or fall off. Subsequent growth of wood may completely conceal the stubs which will remain as knots. No matter how smooth and clear

7387-440: The whole or part of the ship, its cargo, or its equipment. An example was the salvage of the scuttled German High Seas Fleet at Scapa Flow in the 1920s and 1930s. The unauthorized salvage of wrecks is called wrecking . Shipwreck law determines important legal questions regarding wrecks, perhaps the most important question being the question of ownership. Legally wrecks are divided into wreccum maris (material washed ashore after

7476-418: The wood formed, though it is not possible to formulate a rule governing it. In general, where strength or ease of working is essential, woods of moderate to slow growth should be chosen. In ring-porous woods, each season's growth is always well defined, because the large pores formed early in the season abut on the denser tissue of the year before. In the case of the ring-porous hardwoods, there seems to exist

7565-474: The wreck of Cita in 1997. Historic wrecks (often but not always defined as being more than 50 years of age) are often protected from pillaging and looting through national laws protecting cultural heritage. Internationally they may be protected by a State ratifying the Unesco Convention on the Protection of the Underwater Cultural Heritage . In this case pillaging is not allowed. One such example

7654-413: The wreck. On the seabed, wrecks are slowly broken up by the forces of wave action caused by the weather and currents caused by tides . Also, more highly oxygenated water, which promotes corrosion , reduces the strength of ferrous structural materials of the ship. Deeper wrecks are likely to be protected by less exposure to water movement and by lower levels of oxygen in water. Extreme cold (such as in

7743-416: The wreckage collapses. Wrecks supported by a rocky seabed tend to collapse over and around the rocks relatively rapidly. Submarines tend to last longer as they are built much more strongly to withstand the working loads of external pressure, and may last for centuries. A shipwreck may have value in several forms: Often, attempts are made to salvage shipwrecks, particularly those recently wrecked, to recover

7832-499: Was confusion in the press and by the authorities about whether people could be prevented from helping themselves to the flotsam which was washed up on the beaches at Branscombe . Many people took advantage of the confusion and helped themselves to the cargo. This included many BMW motorbikes and empty wine casks as well as bags of disposable nappies ( diapers ). The legal position under the Merchant Shipping Act 1995

7921-406: Was in when it sank. Stratification includes several different types of sand and silt, as well as tumulus and encrustations. These "sediments" are tightly linked to the type of currents, depth, and the type of water (salinity, pH, etc.), which implies any chemical reactions that would affect potential cargo (such as wine, olive oil, spices, etc.). Besides this geological phenomenon, wrecks also face

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