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| *''a brand name of milk ]''. | *''a brand name of milk ]''. | ||
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| = ] = | |||
| <div style="float: right; margin-left: 1em; margin-bottom: 1ex; width: 297px; text-align: center;"> | |||
| ]<br /> | |||
| <small>Ship's anchor</small> | |||
| </div> | |||
| The purpose of a ship's or boat's '''anchor''' is to attach the vessel to the ground at a specific point. There are two primary classes of anchors - temporary and permanent. A permanent anchor is often called a '''mooring''', and is rarely moved; it's quite possible the vessel cannot hoist it aboard but must hire a service to move or maintain it. A temporary anchor is usually carried by the vessel, and is usually hoisted aboard whenever the vessel is under way. | |||
| An '''anchor''' is an instrument of ] or other heavy material used for holding ]s or ]s in position and preventing them from drifting by | |||
| winds, tides, currents or other causes. The anchor is dropped to the ], with one end attached to the ship by means of the ] or ]. Anchors are designed to fix themselves in the ground, there by holding the vessel fast. | |||
| How the anchor works is by resisting the movement force of the vessel which is attached to it. There are two primary ways to do this - via sheer mass, and by "hooking" into the ]. It may seem logical to think wind and currents are the largest forces an anchor must overcome, but actually the vertical movement of waves develop the largest loads, and modern anchors are designed to use a combination of technique and shape to resist all these forces. | |||
| The word "anchor" is also used figuratively for anything which gives security, or for any ornament or appendage which takes the same form. Owing to a vessel's safety depending upon the anchor, it is obviously an appliance of great importance, and too much care cannot be expended on its manufacture and proper construction. The word is from the ] ''agkura'', which Vossius considers is from ''ogke'', a crook or hook. | |||
| == Description == | |||
| ] | |||
| The kind of anchor you probably envision is a temporary anchor; the kind which might be carried aboard a ] or a ]. A modern temporary anchor usually consists of a central bar called the '''shank''', and an armature with some form of flat surface ('''fluke''' or '''palm''') to grip the bottom and a point to assist penetration of the bottom; the position at which the armature is attached to the shank is called the '''crown''', and the shank is usually fitted with a ring or shackle to attach it to the ]. There are many variations and additions to these basic elements; for example the whole class of anchors which include a '''stock''' such as the ] and ] anchors. | |||
| A permanent anchor, on the other hand, may come in a wide range of types and has no standard form. A slab of rock with an iron '''staple''' in it to attach a chain to serves very well, as does a chevy long-block motor. But modern moorings may be anchored by sand screws which look and act very much like over-sized screws drilled into the seabed, or by barbed metal beams pounded in (or even driven in with explosives) like pilings, or a variety of other non-mass means of getting a grip on the bottom. One method of building a mooring is to use three or more temporary anchors laid out with short lengths of chain attached to a swivel, so no matter which direction the vessel moves one or more anchors will be aligned to resist the force. | |||
| == Use of anchors == | |||
| An anchor is one of the most important pieces of equipment on a ship. Although many modern vessels never anchor in normal service, the ability to anchor in the event of breakdown or other accident is essential to prevent the vessel drifting into further danger. Most ships will carry more than one anchor. The primary anchor (or anchors, where one is fitted on each side of the ship) is called the '''bower anchor'''. A secondary anchor, especially one mounted at the ] of a vessel, is called a '''kedge'''. | |||
| == Development == | |||
| An anchor must hold the vessel in place. The larger the vessel, the more "holding power" is required to prevent the vessel from drifting. If the force of the weather and sea on the vessel exceeds the anchor's holding power, the anchor will drag, and if not reset the vessel will drift. The holding power of an anchor depends on its design, its weight and the type of seabed in which it is embedded. On some surfaces (e.g. weed) it may be very hard to get a good hold with many anchors. | |||
| The earliest anchors were probably rocks; many modern moorings still rely on a large rock as the primary element of their design. It simply works. However, using pure mass to resist the forces of a storm only works well as a permanent mooring; trying to move a large enough rock to another bay is nearly impossible. | |||
| There are several different designs of anchor in modern use. The "traditional" anchor is a fisherman anchor. Although they are extremely effective they need to be heavier than many modern designs to achieve the same holding power, and they are awkward to store on deck when the vessel is under way or moored. Anchors in common modern use include the '''CQR''' (pronounced "secure"), the '''Danforth''' and the '''Bruce'''. | |||
| A simple anchor using a pair of wood arms under a rock mass is a primitive anchor which is still in use today. The wood arms a pointed to penetrate the bottom, and the mass will overcome normal movement forces. Together they comprise what may have been the first successful attempts to hook into the seabed and use the mass of the planet to prevent a vessel from moving. Almost all future anchor developments combine these two elements - a penetrating point and a reasonable mass. | |||
| To be most effective the line from the anchor to the ship must lie horizontally along the seabed, as any upwards angle will cause the anchor to "break out" of the seabed, and it will not hold. For this reason a ship will normally lay out a length of chain several times the depth of the water to the anchor. This means that the vessel is not fixed in a single position, but can drift in a cirle limited by the length of chain that has been paid out. This limits how close vessels can lie to each other in an ]. | |||
| In the western world the vast majority of anchors worked on the concept of the grappling hook - multiple points on arms such that at least one will be aimed toward the bottom. [Suddenly the concept of the stock, a bar placed perpendicular to the hooking arm at the other end of the shank which would roll the anchor over so the point would penetrate the bottom, was developed and within a single century became the standard anchor type. | |||
| == History == | |||
| In the East, however, another model of anchor had been known for some time which also used a stock, but with the stock was located at the crown along with the arm. This successful model is still built today in virtually unchanged form. It also informed such modern designs as the ]'s stockless Mark IV. | |||
| The most ancient anchors consisted of large stones, baskets full of stones, sacks filled with sand, or logs of wood loaded with ]. Of this kind were the anchors of the ancient Greeks, which, according to ] and Stephen of ], were formed of stone; and ] states that they were sometimes made of ]. Such anchors held the vessel merely by their weight and by the ] along the bottom. Iron was afterwards introduced for the construction of anchors, and an improvement was made by forming them with teeth or ''flukes'' to fasten themselves into the bottom; whence the words ''odontes'' and ''dentes'' are frequently taken for anchors in the Greek and ] poets. The invention of the teeth is ascribed by ] to the ]s; but ] gives the credit to ], king of ]. Originally there was only one fluke or tooth, whence anchors were called ''eterostomoi''; but a second was added, according to Pliny, by Eupalamus, or, according to Strabo, by Anacharsis, the Scythian philosopher. The anchors with two teeth were called ''amfiboloi'' or ''amfistomoi,'' and from ancient monuments appear to have resembled generally those used in modern days, except that the stock is absent from them all. Every ship had several anchors; the largest, corresponding to our sheet anchor, was only used in extreme danger, and was hence peculiarly termed ''iera'' or ''sacra'', whence the proverb ''sacram anchoram solvere'', as flying to the last refuge. | |||
| == Designs of Temporary Anchors == | |||
| <div style="float: left; margin-right: 1em; margin-bottom: 1ex; width: 318px; text-align: center;"> | |||
| ]<br /> | |||
| <small>Porters/Trotmans anchor</small> | |||
| </div> | |||
| The range of designs is wide, but there are actually trends in designs for modern anchors which allow them to be classed as '''hook''', '''plow''', and '''fluke''' types, depending on the method by which they set. | |||
| Until the beginning of the ] anchors were of imperfect manufacture, the means of effecting good and efficient welding being absent and the iron poor, whilst the arms, being straight, generally parted at the crown, when weighing from good holding-ground. A clerk in ] Yard, named Pering, in the early part of that century (]) introduced curved arms; and after ] the Admiralty anchor, under the direction of the Board, was supplied to H.M. ships, followed by ] (afterwards ]) Rodger's anchor. This marked a great departure from the form of previous anchors. The arms were formed in one piece, and were pivoted at the crown on a bolt passing through the forked shank. The points or pees to the palms were blunt. This anchor had an excellent reputation amongst nautical men of that period, and by the committee on anchors, appointed by the admiralty in ], it was placed second only to the anchor of Trotman. Later came the self-canting anchor, which, passing through successive improvements, became the improved Martin anchor made of forged iron. A projection in the centre of the arms works in a recess at the hub of the shank: the vacancies outside the shank are filled by blocks bolted through on each side, and are flush with the side plates, which keep the flukes in position. | |||
| * '''Hook''' designs use a relatively small fluke surface on a heavy, narrow arm to penetrate deeply into problematic bottoms such as rocky, heavy kelp or eel grass, coral, or hard sand. Two of the more common versions of this design are the ] and the ]. | |||
| The introduction of cast ] in ] led to the improved Martin-Adelphi pattern, in which the crown and arms are cast in one, and, with the stock, are made of cast steel, the shank remaining of forged iron. A projection in the crown works in a recess, and is secured in its place by a forged steel pin, fitted with a nut and washer, which passes through the crown and the heel of the shank. All the above anchors were provided with a stock, the use of which is to "cant" the anchor. If it falls on the ground, resting on one arm and one stock, when a strain is brought on the cable, the stock cants the anchor, causing the arms to lie at a downward angle to the holding ground; and the | |||
| pees enter and bury themselves below the surface of the soil. | |||
| To stow a stocked anchor on the ], it is hove up close to the forefoot, and by means of a ground chain (secured to a balancing or gravity band on the anchor), which is joined to a catting chain rove through a cat davit, the anchor is hove up horizontally and placed on its bed, where it is secured by chains passing over a rod fitted with a lever for "letting go." The cat davit is hinged at its base, and can be laid flat on the deck for right ahead fire or when at sea. Ground and catting chains have been superseded in some ships by a wire pendant and cat hook; the anchor is then hove close up to the hawse-pipe. To avoid cutting away a portion of the forecastle, in the "Cressy," "Terrible" and "Diadem" classes of the ], the anchors, secured by chains, are stowed a-cock-bill, outside the ship, with their crowns resting on iron shoes secured to the ship's side and the flukes fore and aft. A difficulty is experienced in stowing the anchors when the ship is pitching or rolling heavily. Fig. 4 illustrates an anchor with cat davit or anchor crane used in the P. and O. Company's steamers ("India" class, 8000 tons); for sea the anchor is stowed on board by the anchor crane. | |||
| * '''Plow''' designs are reminiscent of the antique farm plow, and are designed to bury themselves the bottom as force is applied to them, and are considered good in most bottom conditions from soft mud to rock. '''Northsea''' designs are actually a variation of a plow in how they work; they bury into the bottom using their shape. | |||
| Stockless anchors have been extensively used in the British mercantile marine and in some foreign navies. In ] they were adopted generally for the British navy, after extensive anchor trials, begun in ]. Their advantages are: | |||
| * handiness combined with a saving of time and labour; | |||
| * absence of davits, anchor-beds and other gear, with a resulting reduction in weight; | |||
| * a clear forecastle for "right ahead" gun fire or for working ship. | |||
| * '''Fluke''' designs use large fluke surfaces to develop very large resistance to loads once they dig into the seabed. Although they have less ability to penetrate and are designed to reset rather than turn, their light weight makes them very popular. | |||
| On the other hand a larger hawse-pipe is required, and there appears to be a consensus of opinion that a stockless anchor when "let go" does not hold so quickly as a stocked one, is more uncertain in its action over uneven ground, and is more liable to "come home" (drag). The stockless anchors principally in use in the British navy are Hall's improved, Byer's, and Wasteneys Smith's. In Hall's | |||
| improved the arms and crown of cast steel are in one piece, and the shank of forged steel passes up through an aperture in the crown to which it is secured by two cross bolts. Two trunnions or lugs are forged to the lower end of the shank. In Byer's plan the flukes and crown consist of a steel-casting secured to a forged shank by a through bolt of mild steel, the axis of which is parallel to the points of the flukes; one end of the bolt has a head, but the other is screwed and fitted with a phosphor bronze nut to allow the bolt to be withdrawn for examination. A palm is cast on each side of the crown to trip the flukes when the anchor is on the ground, and for bringing them snug against the ship's side when weighing. Wasteneys Smith's anchor is composed of three main parts, the shank and crown which form one forging, and the two flukes or arms which are separate castings. A bolt passes through the crown of the anchor, connecting the flukes to it; to prevent the flukes working off the connecting through bolt, two smaller bolts pass through the flukes at right angles to the through bolt and are recessed half their diameter into it. | |||
| === Fisherman === | |||
| Stern, stream and kedge anchors are usually stowed with special davits. A portable anchor suitable for small yachts is the invention of Mr Louis Moore; the shank passes through the crown of the anchor like the handle of a pickaxe and the stock over the head of the shank. At the end of the stock are loose pawls. There are no keys or bolts, and the only fastening is for the cable. The anchor | |||
| ] | |||
| takes to pieces readily and stows snugly. In ] Colonel Bucknill also invented a portable anchor for small yachts. | |||
| A traditional design, the fisherman is familiar to people who've never used an anchor. The design is a non-burying type, with one arm penetrating the seabed and the other standing proud. The anchor is popular as the ultimate storm anchor, and has a good reputation for use in rock, hard bottoms, and kelp or eel grass covered bottoms. The three piece versions can be stowed quite compactly, and most versions include a folding stock so the anchor may be stowed flat on deck. | |||
| The primary weakness of the design is its ability to foul the cable over changing tides. Once fouled the anchor is likely to drag. In comparison tests the fisherman design developed much less resistance than other anchors of similar weight. It is difficult to bring aboard without scarring the topsides, and does not stow in a hawse pipe or over an anchor roller. | |||
| <div style="float: right; margin-left: 1em; margin-bottom: 1ex; width: 295px; text-align: center;"> | |||
| <br style="clear:both;" /> | |||
| ]<br /> | |||
| <small>Marine anchor</small> | |||
| </div> | |||
| === Fluke === | |||
| Iron ]-sinkers, as used by the ] corporation of ], weigh from 8 to 40 ] (400 to 2,000 ]); the specified weight is cast on them in large raised figures, and the | |||
| cast and wrought irons used are of special quality, of which samples are previously submitted to the engineer-in-chief. | |||
| The most common commercial brand is the "'''Danforth'''", which is sometimes used as a generic name for the class. The fluke style uses a stock at the crown to which two large flat surfaces are attached. The stock is hinged so the flukes can orient toward the bottom (and on some designs may be adjusted for an optimal angle depending on the bottom type.) The design is a burying variety, and once well set can develop an amazing amount resistance. Its light weight and compact flat design make it easy to retrieve and relatively easy to store; some anchor rollers and hawse pipes can accommodate a fluke-style anchor. A few high-performance designs are available, such as the "'''Fortress'''", which are lighter in weight for a given area and in tests have shown better than average results. | |||
| The anchors supplied to ships of the ] are required to withstand a certain tensile strain, expressed in tons, proportionate to their weights in cwts. New anchors are supplied by contractors, but repairs are made in H.M. dockyards, a record of its repairs being stamped on each anchor. In | |||
| the Anchors and Cables Act ] a list is given of authorized testing-establishments, with their distinctive marks and charges, and testing- houses for foreign-owned vessels are enumerated in Table 22 of Lloyd's Register of British and Foreign Shipping. Cast-steel anchors, in addition to the | |||
| statutory tests, are subjected to percussive, hammering and bending tests, and are stamped "annealed steel." | |||
| The fluke anchor has difficulty penetrating kelp and weed-covered bottoms, as well as rocky and particularly hard sand or clay bottoms. If there is much current or the vessel is moving while dropping the anchor it may "kite" or "skate" over the bottom due to the large fluke area acting as a sail or wing. Once set, the anchor tends to break out and reset when the direction of force changes dramatically, such as with the changing tide, and on some occasions it might not reset but instead drag. | |||
| In addition to keeping motionless, an anchor may be utilized as an instrument of propulsion in ]. | |||
| ] | |||
| <br style="clear:both;" /> | |||
| === Grapnel === | |||
| ] | |||
| A traditional design, the grapnel style is simple to design and build. It has a benefit in that no matter how it reaches the bottom one or more tines will be aimed to set. The design is a non-burying variety, with one or more tines digging in and the remainder above the seabed. In coral it is often able to set quickly by hooking into the structure, but may be more difficult to retrieve. A grapnel is often quite light, and may have additional uses as a tool to recover gear lost overboard; its weight also makes it relatively easy to bring aboard. | |||
| Grapnels rarely have enough fluke area to develop much hold in sand, clay, or mud. It is not unknown for the anchor to foul on its own rode, or to foul the tines with refuse from the bottom, preventing it from digging in. It is quite possible for this anchor to find such a good hook that, without a trip line, it is impossible to retrieve. The shape is generally not very compact, and is difficult to stow, although there are a few collapsing designs available. | |||
| ---- | |||
| <br style="clear:both;" /> | |||
| {{1911}} | |||
| === North sea === | |||
| ] | |||
| Designed originally for anchoring floating oil derricks in the ], this versatile design has become a popular option for smaller boaters as well. The burying design acts similarly to a large scoop, and is known for the speed with which it digs in. Although not an articulated design, it has the reputation of not breaking out with tide or wind changes, instead slowly turning in the bottom to align with the force. Some versions of the design, such as the "'''Bruce'''", are reputed to be easy to retrieve once broken out of the bottom, and some anchor rollers can accommodate their shank. | |||
| North sea designs may have difficulty penetrating weedy bottoms, rock, and coral. They can be particularly difficult to break out. Although they can be got aboard without scarring the topsides, they take up an inordinate amount of locker space. They cannot be used with hawse pipes. | |||
| <br style="clear:both;" /> | |||
| === Plow === | |||
| ]] | |||
| Several companies produce a plow-style design, and they are particularly popular with cruising sailors. Plows are generally good in all bottoms, but not exceptional in any. The "'''CQR'''" design has a hinged shank, allowing the anchor to turn with direction changes rather than breaking out, and also arranged to force the point of the plow into the bottom if the anchor lands on its side. Another commercial design, the "'''Delta'''" uses an unhinged shank and a plow with specific angles to develop very similar performance. Both can be stored in some anchor roller designs. | |||
| The plow is heavier than the average for the amount of resistance developed, and may take slightly longer pull to set thoroughly. It cannot be stored in a hawse pipe. | |||
| <br style="clear:both;" /> | |||
| == Anchoring Techniques == | |||
| Heaving an anchor over the side is not good enough. There are several elements to anchor gear to be considered, and there are techniques to ensure a good '''set'''. This article can discuss some of this information, but it is by no means a treatise for safe anchoring. | |||
| === Anchoring gear === | |||
| The elements of anchoring gear include the anchor, the '''cable''' (also called a '''rode'''), the method of attaching the two together, the method of attaching the cable to the ship, '''charts''', and a method of learning the depth of the water. | |||
| Charts are vital to good anchoring. Knowing the location of potential dangers, as well as being useful in estimating the effects of weather and tide in the anchorage, is essential in choosing a good place to drop the hook. One can get by without refering to charts, but they are an important tool and a part of good anchoring gear, and a skilled mariner would not choose to anchor without them. | |||
| The depth of water is necessary for determining '''scope''', which is the ratio of length of cable to the depth measured from the highest point (usually the anchor roller or bow chock) to the seabed. For example, if the water is 25ft (8m) deep, and the anchor roller is 3ft (1m) above the water, the scope is the ratio between the amount of cable let out and 28ft (9m). For this reason it is important to have a reliable and accurate method of measuring the depth of water. | |||
| A '''cable''' or '''rode''' is the rope, chain, or combination thereof used to connect the anchor to the vessel. Neither rope nor chain is fundamentally superior as a cable or there would not be continued argument over the issue; each has its strengths and its weaknesses and it is not the purpose of this article to address these. | |||
| === Anchoring === | |||
| The four primary questions to be considered before actually anchoring: | |||
| :# Is the anchorage protected? | |||
| :# Is the seabed good holding ground? | |||
| :# What is the depth, tidal range, and the current tide state? | |||
| :# Is there enough room? | |||
| ==== 1. Is the anchorage protected? ==== | |||
| A good anchorage offers protection from the current weather conditions, and will also offer protection from the expected weather. You should also consider if the anchorage will be suitable for other purposes, for example can you get safely to shore in your dinghy if that is one of your goals. And keep in mind comfort; a rolly harbor is no fun. | |||
| ==== 2. Is the seabed good holding ground? ==== | |||
| You should have charts to indicate the kind of bottom, as well as a tool such as a ] to collect a sample from the bottom. Generally speaking, most anchors will hold well in sandy mud, mud and clay, or firm sand. Loose sand and soft mud are not desirable bottoms, and especially soft mud which should be avoided if at all possible. Rock, coral, and shale prevent anchors from digging in, although some anchors are designed to hook into such a bottom. Grassy bottoms may be good holding, but only if the anchor can penetrate the bottom. | |||
| ==== 3. What is the depth, tidal range, and the current tide state? ==== | |||
| If your anchorage is affected by ], you need to know the tide range and the times of high and low water. You need enough depth for your vessel throughout the range it might swing, at low tide, not just where you drop the anchor. This is also important when determining ], which should be figured for high tide and not the current tide state. | |||
| ==== 4. Is there enough room? ==== | |||
| If your anchorage is affected by tide, you should keep in mind that the swing range will be larger at low tide than at high tide. However, no matter where you anchor you need to consider what the larges possible swing range will be, and what obstacles and hazards might be within that range. Keep in mind that other vessels in the anchorage may have a swing range which can overlap yours. Boats on permanent moorings, or shorter scope, may not swing as far as you expect them to, or may swing either more rapidly or more slowly than your vessel (all-chain cables tend to swing more slowly than all-rope or chain-and-rope cables.) | |||
| There are techniques of anchoring to limit the swing of a vessel if the anchorage has limited room. | |||
| === Methods === | |||
| The basic anchoring consists of determining the location, dropping the anchor, laying out the scope, setting the hook, and assessing where the vessel ends up. After figuring out on the chart where a desirable location would be, the vessel need to actually see what the situation is like; there may be other boats who thought that would be a good spot, or weather conditions are different than expected, or even additional hazards not noted on the chart which make a planned location undesirable. | |||
| If the location is good, the location to drop the anchor should be approached from down wind or down current, whichever is stronger. As the chosen spot is approached, the vessel should be stopped or even beginning to drift back. The anchor should be lowered quickly but under control until it is on the bottom. The vessel should continue to drift back, and the cable should be veered out under control so it will be relatively straight. | |||
| Once the desired scope is laid out (hopefully at least 5:1 for setting the anchor), the vessel should be gently forced astern, usually using the auxilliary motor but possibly by backing a sail. A hand on the anchor line may telegraph a series of jerks and jolts, indicating the anchor is dragging, or a smooth tension indicative of digging in. As the anchor begins to dig in and resist backward force, the engine may be throttled up to get a thorough set. If the anchor continues to drag, or sets after having dragged to far, it should be retrieved and moved back to the desired position (or another location chosen.) | |||
| With the anchor set in the correct location, everything should be reconsidered. Is the location protected, now and for the forecast weather? Is the bottom a suitable holding ground, and is the anchor the right one for this type of bottom? Is there enough depth, both now and at low tide? Especially at low tide but also at all tide states, is there enough room for the boat to swing? Will another vessel swing into us, or will we swing into another vessel, when the tide or wind changes? | |||
| Some other techniques have been developed to reduce swing, or to deal with heavy weather. | |||
| :* ] | |||
| :* ] | |||
| :* ] | |||
| :* ] | |||
| ==== Forked moor ==== | |||
| Using two anchors set approximately 45° apart, or wider angles up to 90°, from the bow is a strong mooring for facing into strong winds. To set anchors in this way, first one anchor is set in the normal fashion. Then, taking in on the first cable as the boat is motored into the wind and letting slack while drifting back, a second anchor is set approximately a half-scope away from the first on a line perpendicular to the wind. After this second anchor is set, the scope on the first is taken up until the vessel is lying between the two anchors and the load is taken equally on each cable. | |||
| This moor also to some degree limits the range of a vessel's swing to a narrower oval. Care should be taken that other vessels will not swing down on the boat due to the limited swing range. | |||
| ==== Bow and Stern ==== | |||
| Not to be mistaken with the ''']''', below. | |||
| In the '''Bow and Stern''' technique, an anchor is set off each the bow and the stern, which can severely limit a vessel's swing range and also align it to steady wind, current or wave conditions. One method of accomplishing this moor is to set a bow anchor normally, then drop back to the limit of the bow cable (or to double the desired scope, e.g. 8:1 if the eventual scope should be 4:1, 10:1 if the eventual scope should be 5:1, etc.) to lower a stern anchor. By taking up on the bow cable the stern anchor can be set. After both anchors are set, tension is taken up on both cables to limit the swing or to align the vessel. | |||
| ==== Bahamian moor ==== | |||
| Similar to the above, a '''Bahamian moor''' is used to sharply limit the swing range of a vessel, but allows it to swing to a current. One of the primary characteristics of this technique is the use of a swivel as follows: the first anchor is set normally, and the vessel drops back to the limit of anchor cable. A second anchor is attached to the end of the anchor cable, and is dropped and set. A swivel is attached to the middle of the anchor cable, and the vessel connected to that. | |||
| The vessel will now swing in the middle of two anchors, which is acceptable in strong reversing currents but a wind perpendicular to the current may break out the anchors as they are not aligned for this load. | |||
| ==== Backing an anchor ==== | |||
| Also known as '''Tandem anchors''', in this technique two anchors are shackled to a single cable running crown-to-shank. With the leading anchor holding the cable down and the tension between the anchors taking load off, this technique can develop great holding power and has been used in "ultimate storm" circumstances. It does not limited swinging range, and might not be appropriate for crowded anchorages. | |||
| == References == | |||
| * Edwards, Fred (illustrated Sollers, Jim); <u>Sailing as a Second Language: An illustrated dictionary</u>; © 1988 Highmark Publishing Ltd; ISBN 0-87742-965-0 | |||
| * Hiscock, Eric C.; <u>Cruising Under Sail, second edition</u>; Oxford University Press; © 1965 Oxford University Press; ISBN 0-19-217522-X | |||
| * Pardey, Lin and Larry; <u>The Capable Cruiser</u>; Pardey Boooks/Paradise Cay Publications; © 1995 Lin and Larry Pardey; ISBN 0-9646036-2-4 | |||
| * Rousmaniere, John; <u>The Annapolis Book of Seamanship</u>; Simon and Schuster; © 1983, 1989 John Rousmaniere; ISBN 0-671-67447-1 | |||
| * Smith, Everrett; Cruising World's <u>Guide to Seamanship: Hold me tight</u>; © 1992 New York Times Sports/Leisure Magazines | |||
| ] | ] | ||
Revision as of 05:57, 25 November 2004
An anchor is also:
- the name of the host of a television news program: see news anchor.
- the source and destination of a hyperlink.
- in psychology, sticking to a given reference point: see anchoring.
- a brand name of milk Anchor Milk.
Anchor
The purpose of a ship's or boat's anchor is to attach the vessel to the ground at a specific point. There are two primary classes of anchors - temporary and permanent. A permanent anchor is often called a mooring, and is rarely moved; it's quite possible the vessel cannot hoist it aboard but must hire a service to move or maintain it. A temporary anchor is usually carried by the vessel, and is usually hoisted aboard whenever the vessel is under way.
How the anchor works is by resisting the movement force of the vessel which is attached to it. There are two primary ways to do this - via sheer mass, and by "hooking" into the seabed. It may seem logical to think wind and currents are the largest forces an anchor must overcome, but actually the vertical movement of waves develop the largest loads, and modern anchors are designed to use a combination of technique and shape to resist all these forces.
Description
a. Shank
b. Crown
c. Arm
d. Fluke
e. Point
f. & g. Eye and Ring
h. Stock
i. Fisherman's bend
The kind of anchor you probably envision is a temporary anchor; the kind which might be carried aboard a ship or a boat. A modern temporary anchor usually consists of a central bar called the shank, and an armature with some form of flat surface (fluke or palm) to grip the bottom and a point to assist penetration of the bottom; the position at which the armature is attached to the shank is called the crown, and the shank is usually fitted with a ring or shackle to attach it to the cable. There are many variations and additions to these basic elements; for example the whole class of anchors which include a stock such as the fisherman and fluke anchors.
A permanent anchor, on the other hand, may come in a wide range of types and has no standard form. A slab of rock with an iron staple in it to attach a chain to serves very well, as does a chevy long-block motor. But modern moorings may be anchored by sand screws which look and act very much like over-sized screws drilled into the seabed, or by barbed metal beams pounded in (or even driven in with explosives) like pilings, or a variety of other non-mass means of getting a grip on the bottom. One method of building a mooring is to use three or more temporary anchors laid out with short lengths of chain attached to a swivel, so no matter which direction the vessel moves one or more anchors will be aligned to resist the force.
Development
The earliest anchors were probably rocks; many modern moorings still rely on a large rock as the primary element of their design. It simply works. However, using pure mass to resist the forces of a storm only works well as a permanent mooring; trying to move a large enough rock to another bay is nearly impossible.
A simple anchor using a pair of wood arms under a rock mass is a primitive anchor which is still in use today. The wood arms a pointed to penetrate the bottom, and the mass will overcome normal movement forces. Together they comprise what may have been the first successful attempts to hook into the seabed and use the mass of the planet to prevent a vessel from moving. Almost all future anchor developments combine these two elements - a penetrating point and a reasonable mass.
In the western world the vast majority of anchors worked on the concept of the grappling hook - multiple points on arms such that at least one will be aimed toward the bottom. [Suddenly the concept of the stock, a bar placed perpendicular to the hooking arm at the other end of the shank which would roll the anchor over so the point would penetrate the bottom, was developed and within a single century became the standard anchor type.
In the East, however, another model of anchor had been known for some time which also used a stock, but with the stock was located at the crown along with the arm. This successful model is still built today in virtually unchanged form. It also informed such modern designs as the US Navy's stockless Mark IV.
Designs of Temporary Anchors
The range of designs is wide, but there are actually trends in designs for modern anchors which allow them to be classed as hook, plow, and fluke types, depending on the method by which they set.
- Hook designs use a relatively small fluke surface on a heavy, narrow arm to penetrate deeply into problematic bottoms such as rocky, heavy kelp or eel grass, coral, or hard sand. Two of the more common versions of this design are the fisherman and the grapnel.
- Plow designs are reminiscent of the antique farm plow, and are designed to bury themselves the bottom as force is applied to them, and are considered good in most bottom conditions from soft mud to rock. Northsea designs are actually a variation of a plow in how they work; they bury into the bottom using their shape.
- Fluke designs use large fluke surfaces to develop very large resistance to loads once they dig into the seabed. Although they have less ability to penetrate and are designed to reset rather than turn, their light weight makes them very popular.
Fisherman
A traditional design, the fisherman is familiar to people who've never used an anchor. The design is a non-burying type, with one arm penetrating the seabed and the other standing proud. The anchor is popular as the ultimate storm anchor, and has a good reputation for use in rock, hard bottoms, and kelp or eel grass covered bottoms. The three piece versions can be stowed quite compactly, and most versions include a folding stock so the anchor may be stowed flat on deck.
The primary weakness of the design is its ability to foul the cable over changing tides. Once fouled the anchor is likely to drag. In comparison tests the fisherman design developed much less resistance than other anchors of similar weight. It is difficult to bring aboard without scarring the topsides, and does not stow in a hawse pipe or over an anchor roller.
Fluke
The most common commercial brand is the "Danforth", which is sometimes used as a generic name for the class. The fluke style uses a stock at the crown to which two large flat surfaces are attached. The stock is hinged so the flukes can orient toward the bottom (and on some designs may be adjusted for an optimal angle depending on the bottom type.) The design is a burying variety, and once well set can develop an amazing amount resistance. Its light weight and compact flat design make it easy to retrieve and relatively easy to store; some anchor rollers and hawse pipes can accommodate a fluke-style anchor. A few high-performance designs are available, such as the "Fortress", which are lighter in weight for a given area and in tests have shown better than average results.
The fluke anchor has difficulty penetrating kelp and weed-covered bottoms, as well as rocky and particularly hard sand or clay bottoms. If there is much current or the vessel is moving while dropping the anchor it may "kite" or "skate" over the bottom due to the large fluke area acting as a sail or wing. Once set, the anchor tends to break out and reset when the direction of force changes dramatically, such as with the changing tide, and on some occasions it might not reset but instead drag.
Grapnel
A traditional design, the grapnel style is simple to design and build. It has a benefit in that no matter how it reaches the bottom one or more tines will be aimed to set. The design is a non-burying variety, with one or more tines digging in and the remainder above the seabed. In coral it is often able to set quickly by hooking into the structure, but may be more difficult to retrieve. A grapnel is often quite light, and may have additional uses as a tool to recover gear lost overboard; its weight also makes it relatively easy to bring aboard.
Grapnels rarely have enough fluke area to develop much hold in sand, clay, or mud. It is not unknown for the anchor to foul on its own rode, or to foul the tines with refuse from the bottom, preventing it from digging in. It is quite possible for this anchor to find such a good hook that, without a trip line, it is impossible to retrieve. The shape is generally not very compact, and is difficult to stow, although there are a few collapsing designs available.
North sea
Designed originally for anchoring floating oil derricks in the North Sea, this versatile design has become a popular option for smaller boaters as well. The burying design acts similarly to a large scoop, and is known for the speed with which it digs in. Although not an articulated design, it has the reputation of not breaking out with tide or wind changes, instead slowly turning in the bottom to align with the force. Some versions of the design, such as the "Bruce", are reputed to be easy to retrieve once broken out of the bottom, and some anchor rollers can accommodate their shank.
North sea designs may have difficulty penetrating weedy bottoms, rock, and coral. They can be particularly difficult to break out. Although they can be got aboard without scarring the topsides, they take up an inordinate amount of locker space. They cannot be used with hawse pipes.
Plow
Several companies produce a plow-style design, and they are particularly popular with cruising sailors. Plows are generally good in all bottoms, but not exceptional in any. The "CQR" design has a hinged shank, allowing the anchor to turn with direction changes rather than breaking out, and also arranged to force the point of the plow into the bottom if the anchor lands on its side. Another commercial design, the "Delta" uses an unhinged shank and a plow with specific angles to develop very similar performance. Both can be stored in some anchor roller designs.
The plow is heavier than the average for the amount of resistance developed, and may take slightly longer pull to set thoroughly. It cannot be stored in a hawse pipe.
Anchoring Techniques
Heaving an anchor over the side is not good enough. There are several elements to anchor gear to be considered, and there are techniques to ensure a good set. This article can discuss some of this information, but it is by no means a treatise for safe anchoring.
Anchoring gear
The elements of anchoring gear include the anchor, the cable (also called a rode), the method of attaching the two together, the method of attaching the cable to the ship, charts, and a method of learning the depth of the water.
Charts are vital to good anchoring. Knowing the location of potential dangers, as well as being useful in estimating the effects of weather and tide in the anchorage, is essential in choosing a good place to drop the hook. One can get by without refering to charts, but they are an important tool and a part of good anchoring gear, and a skilled mariner would not choose to anchor without them.
The depth of water is necessary for determining scope, which is the ratio of length of cable to the depth measured from the highest point (usually the anchor roller or bow chock) to the seabed. For example, if the water is 25ft (8m) deep, and the anchor roller is 3ft (1m) above the water, the scope is the ratio between the amount of cable let out and 28ft (9m). For this reason it is important to have a reliable and accurate method of measuring the depth of water.
A cable or rode is the rope, chain, or combination thereof used to connect the anchor to the vessel. Neither rope nor chain is fundamentally superior as a cable or there would not be continued argument over the issue; each has its strengths and its weaknesses and it is not the purpose of this article to address these.
Anchoring
The four primary questions to be considered before actually anchoring:
- Is the anchorage protected?
- Is the seabed good holding ground?
- What is the depth, tidal range, and the current tide state?
- Is there enough room?
1. Is the anchorage protected?
A good anchorage offers protection from the current weather conditions, and will also offer protection from the expected weather. You should also consider if the anchorage will be suitable for other purposes, for example can you get safely to shore in your dinghy if that is one of your goals. And keep in mind comfort; a rolly harbor is no fun.
2. Is the seabed good holding ground?
You should have charts to indicate the kind of bottom, as well as a tool such as a sounding lead to collect a sample from the bottom. Generally speaking, most anchors will hold well in sandy mud, mud and clay, or firm sand. Loose sand and soft mud are not desirable bottoms, and especially soft mud which should be avoided if at all possible. Rock, coral, and shale prevent anchors from digging in, although some anchors are designed to hook into such a bottom. Grassy bottoms may be good holding, but only if the anchor can penetrate the bottom.
3. What is the depth, tidal range, and the current tide state?
If your anchorage is affected by tide, you need to know the tide range and the times of high and low water. You need enough depth for your vessel throughout the range it might swing, at low tide, not just where you drop the anchor. This is also important when determining scope, which should be figured for high tide and not the current tide state.
4. Is there enough room?
If your anchorage is affected by tide, you should keep in mind that the swing range will be larger at low tide than at high tide. However, no matter where you anchor you need to consider what the larges possible swing range will be, and what obstacles and hazards might be within that range. Keep in mind that other vessels in the anchorage may have a swing range which can overlap yours. Boats on permanent moorings, or shorter scope, may not swing as far as you expect them to, or may swing either more rapidly or more slowly than your vessel (all-chain cables tend to swing more slowly than all-rope or chain-and-rope cables.)
There are techniques of anchoring to limit the swing of a vessel if the anchorage has limited room.
Methods
The basic anchoring consists of determining the location, dropping the anchor, laying out the scope, setting the hook, and assessing where the vessel ends up. After figuring out on the chart where a desirable location would be, the vessel need to actually see what the situation is like; there may be other boats who thought that would be a good spot, or weather conditions are different than expected, or even additional hazards not noted on the chart which make a planned location undesirable.
If the location is good, the location to drop the anchor should be approached from down wind or down current, whichever is stronger. As the chosen spot is approached, the vessel should be stopped or even beginning to drift back. The anchor should be lowered quickly but under control until it is on the bottom. The vessel should continue to drift back, and the cable should be veered out under control so it will be relatively straight.
Once the desired scope is laid out (hopefully at least 5:1 for setting the anchor), the vessel should be gently forced astern, usually using the auxilliary motor but possibly by backing a sail. A hand on the anchor line may telegraph a series of jerks and jolts, indicating the anchor is dragging, or a smooth tension indicative of digging in. As the anchor begins to dig in and resist backward force, the engine may be throttled up to get a thorough set. If the anchor continues to drag, or sets after having dragged to far, it should be retrieved and moved back to the desired position (or another location chosen.)
With the anchor set in the correct location, everything should be reconsidered. Is the location protected, now and for the forecast weather? Is the bottom a suitable holding ground, and is the anchor the right one for this type of bottom? Is there enough depth, both now and at low tide? Especially at low tide but also at all tide states, is there enough room for the boat to swing? Will another vessel swing into us, or will we swing into another vessel, when the tide or wind changes?
Some other techniques have been developed to reduce swing, or to deal with heavy weather.
Forked moor
Using two anchors set approximately 45° apart, or wider angles up to 90°, from the bow is a strong mooring for facing into strong winds. To set anchors in this way, first one anchor is set in the normal fashion. Then, taking in on the first cable as the boat is motored into the wind and letting slack while drifting back, a second anchor is set approximately a half-scope away from the first on a line perpendicular to the wind. After this second anchor is set, the scope on the first is taken up until the vessel is lying between the two anchors and the load is taken equally on each cable.
This moor also to some degree limits the range of a vessel's swing to a narrower oval. Care should be taken that other vessels will not swing down on the boat due to the limited swing range.
Bow and Stern
Not to be mistaken with the Bahamian moor, below.
In the Bow and Stern technique, an anchor is set off each the bow and the stern, which can severely limit a vessel's swing range and also align it to steady wind, current or wave conditions. One method of accomplishing this moor is to set a bow anchor normally, then drop back to the limit of the bow cable (or to double the desired scope, e.g. 8:1 if the eventual scope should be 4:1, 10:1 if the eventual scope should be 5:1, etc.) to lower a stern anchor. By taking up on the bow cable the stern anchor can be set. After both anchors are set, tension is taken up on both cables to limit the swing or to align the vessel.
Bahamian moor
Similar to the above, a Bahamian moor is used to sharply limit the swing range of a vessel, but allows it to swing to a current. One of the primary characteristics of this technique is the use of a swivel as follows: the first anchor is set normally, and the vessel drops back to the limit of anchor cable. A second anchor is attached to the end of the anchor cable, and is dropped and set. A swivel is attached to the middle of the anchor cable, and the vessel connected to that.
The vessel will now swing in the middle of two anchors, which is acceptable in strong reversing currents but a wind perpendicular to the current may break out the anchors as they are not aligned for this load.
Backing an anchor
Also known as Tandem anchors, in this technique two anchors are shackled to a single cable running crown-to-shank. With the leading anchor holding the cable down and the tension between the anchors taking load off, this technique can develop great holding power and has been used in "ultimate storm" circumstances. It does not limited swinging range, and might not be appropriate for crowded anchorages.
References
- Edwards, Fred (illustrated Sollers, Jim); Sailing as a Second Language: An illustrated dictionary; © 1988 Highmark Publishing Ltd; ISBN 0-87742-965-0
- Hiscock, Eric C.; Cruising Under Sail, second edition; Oxford University Press; © 1965 Oxford University Press; ISBN 0-19-217522-X
- Pardey, Lin and Larry; The Capable Cruiser; Pardey Boooks/Paradise Cay Publications; © 1995 Lin and Larry Pardey; ISBN 0-9646036-2-4
- Rousmaniere, John; The Annapolis Book of Seamanship; Simon and Schuster; © 1983, 1989 John Rousmaniere; ISBN 0-671-67447-1
- Smith, Everrett; Cruising World's Guide to Seamanship: Hold me tight; © 1992 New York Times Sports/Leisure Magazines