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[edit] Is the anchorage protected?
A good anchorage offers protection from the current weather conditions, and will also offer protection from the expected weather. The anchorage should also be suitable for other purposes; for example, proximity to shore is beneficial if the crew plans to land.
[edit] Is the seabed a good holding ground?
Charts should indicate the type of bottom, and a sounding lead may be used to collect a sample from the bottom for analysis. 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, 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 foliage.
[edit] What is the depth, tidal range, and the current tide state?
If the anchorage is affected by tide, tide ranges, as well as the times of high and low water, should be known. Enough depth is needed so that low tide does not present obstacles to where the vessel might swing. This is also important when determining scope, which should be figured for high tide and not the current tide state.
[edit] Is there enough room?
If the anchorage is affected by tide, one should keep in mind that the swing range will be larger at low tide than at high tide. However, no matter where the vessel is anchored, the largest possible swing range should be considered, as well as what obstacles and hazards might be within that range. Other vessels' swing ranges may overlap, presenting a further variable. Boats on permanent moorings, or shorter scope, may not swing as far as expected, or may swing either more rapidly or more slowly (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.
[edit] Methods
Colored plastic inserts on a modern anchor chain show the operator how much chain has been paid out. This knowledge is very important in all anchoring 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 using the chart to determine a desirable location, the crew needs to actually see what the situation is like; there may be other boats whose crew thought that would be a good spot, or weather conditions may be different from those expected, or even additional hazards not noted on the chart may 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 (a minimum of 8:1 for setting the anchor, and 5:1 for holding, though the preferred ratio is 10:1 for both setting, and holding power), the vessel should be gently forced astern, usually using the auxiliary 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 too 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.
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[edit] Using an anchor weight, kellet or sentinel
Lowering a concentrated, heavy weight down the anchor line - rope or chain - directly in front of the bow to the seabed, behaves like a heavy chain rode and lowers the angle of pull on the anchor.[7] If the weight is suspended off the seabed it acts as a spring or shock absorber to dampen the sudden actions that are normally transmitted to the anchor and can cause it to dislodge and drag. In light conditions, a kellet will reduce the swing of the vessel considerably. In heavier conditions these effects disappear as the rode becomes straightened and the weight ineffective.
[edit] 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.
[edit] 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.
[edit] 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.
[edit] Backing an anchor
Also known as Tandem anchoring, in this technique two anchors are deployed in line with each other, on the same rode. With the foremost anchor reducing the load on the aft-most, this technique can develop great holding power and may be appropriate in "ultimate storm" circumstances. It does not limit swinging range, and might not be suitable in some circumstances. There are complications and the technique requires careful preparation and a level of skill and experience above that required for a single anchor.
[edit] Kedging
Kedging is a technique for moving or turning a ship by using a relatively light anchor known as a kedge.
In yachts, a kedge anchor is an anchor carried in addition to the main, or bower anchors, and usually stowed aft. Every yacht should carry at least two anchors - the main or bower anchor and a second lighter kedge anchor. It is used occasionally when it is necessary to limit the turning circle as the yacht swings when it is anchored, such as in a very narrow river or a deep pool in an otherwise shallow area.
For ships, a kedge may be dropped while a ship is underway, or carried out in a suitable direction by a tender or ship's boat to enable the ship to be winched off if aground or swung into a particular heading, or even to be held steady against a tidal or other stream.
Historically, it was of particular relevance to sailing warships which used them to out-maneuver opponents when the wind had dropped but might be used by any vessel in confined, shoal water to place it in a more desirable position, provided she had enough manpower.
[edit] In Heraldry
An anchor frequently appears on the flags and coats-of-arms of institutions involved with the sea, both naval and commercial, as well as of port cities and sea-coast regions and provinces in various countries.
There also exists in heraldry the "Anchored Cross", or Mariner's Cross, a stylized cross in the shape of an anchor. The symbol can be used to signify 'fresh start' or 'hope'.
The Mariner's Cross is also referred to as St. Clement's Cross in reference to the way this saint was martyred (being tied to an anchor and thrown from a boat into the Black Sea in the year 102). .
Anchored crosses are occasionally a feature of coats of arms in which context they are referred to by the heraldic terms anchry or ancre.
[edit] References
- , Taylor, G. I. (1974). "The history of an invention". Bulletin of the Institute of Mathematics and its Applications 10: 367–368. Cited by Batchelor, G. K. (1986). "Geoffrey Ingram Taylor, 7 March 1886–27 June 1975". Journal of Fluid Mechanics 173: 1–14. doi:10.1017/S0022112086001040.
- , Bruce, Peter, U.S. Patent 4,397,256 August 9, 1983
- , Ginsberg-Klemmt, Erika & Achim, and Poiraud, Alain: "The Complete Anchoring Handbook", Ragged Mountain Press, 2007 (ISBN 0071475087)
- , Practical Sailor: "Anchor Reset Tests", Belvoir Pubs, January 2001
- , Poiraud, Alain: "Tout savoir sur le mouillage", Loisirs Nautiques, 2003 (ISBN 2-914423-46-2)
- , Lowe, Colin: "Gear Test: Rocna Anchor", Boating NZ, July 2006
- , Hinz, Earl R.; The Complete Book of Anchoring and Mooring, first ed., 1986, Cornell Maritime Press; ISBN 0-87033-348-8
- Edwards, Fred; Sailing as a Second Language: An illustrated dictionary, 1988 Highmark Publishing; ISBN 0-87742-965-0
- Hinz, Earl R.; The Complete Book of Anchoring and Mooring, Rev. 2d ed., 1986, 1994, 2001 Cornell Maritime Press; ISBN 0-87033-539-1
- Hiscock, Eric C.; Cruising Under Sail, second edition, 1965 Oxford University Press; ISBN 0-19-217522-X
- Pardey, Lin and Larry; The Capable Cruiser; 1995 Pardey Books/Paradise Cay Publications; ISBN 0-9646036-2-4
- Rousmaniere, John; The Annapolis Book of Seamanship, 1983, 1989 Simon and Schuster; ISBN 0-671-67447-1
- Smith, Everrett; Cruising World's Guide to Seamanship: Hold me tight, 1992 New York Times Sports/Leisure Magazines
[edit] External links
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