Tidal diamonds are symbols on British admiralty charts that indicate the direction and speed of tidal streams.
Admiralty charts are nautical charts issued by the United Kingdom Hydrographic Office (UKHO) and subject to Crown Copyright. Over 3,500 Standard Nautical Charts (SNCs) and 14,000 Electronic Navigational Charts (ENCs) are available with the Admiralty portfolio offering the widest official coverage of international shipping routes and ports, in varying detail.
Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon and the Sun, and the rotation of the Earth.
The symbols consist of a letter of the ISO basic Latin alphabet in a rhombus, printed in purple ink. On any particular chart each tidal diamond will have a unique letter starting from "A" and continuing alphabetically.
The ISO basic Latin alphabet is a Latin-script alphabet and consists of two sets of 26 letters, codified in various national and international standards and used widely in international communication. They are the same letters that comprise the English alphabet.
In plane Euclidean geometry, a rhombus is a simple (non-self-intersecting) quadrilateral whose four sides all have the same length. Another name is equilateral quadrilateral, since equilateral means that all of its sides are equal in length. The rhombus is often called a diamond, after the diamonds suit in playing cards which resembles the projection of an octahedral diamond, or a lozenge, though the former sometimes refers specifically to a rhombus with a 60° angle, and the latter sometimes refers specifically to a rhombus with a 45° angle.
Somewhere on the chart, generally on land, will be a Tidal Diamond table. This contains a grid of thirteen rows and three columns for each Diamond. The rows are the hours of the tidal cycle showing the 6 hours before high water, high water itself and the 6 hours after high water.The columns show the bearing of the tidal stream and its speed, in knots, at both spring tide and neap tide. The times on the table are related to the high water of the standard port displayed on the table.
In navigation, bearing is the horizontal angle between the direction of an object and another object, or between it and that of true north.
The knot is a unit of speed equal to one nautical mile per hour, exactly 1.852 km/h. The ISO standard symbol for the knot is kn. The same symbol is preferred by the Institute of Electrical and Electronics Engineers (IEEE); kt is also common, especially in aviation where it is the form recommended by the International Civil Aviation Organization (ICAO). The knot is a non-SI unit. Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels approximately one minute of geographic latitude in one hour.
A Standard port is a port whose tidal predictions are directly given in the Tide tables.
An alternative to a tidal diamond is a tidal atlas which are often more accurate and easier to use (if available).
A tidal atlas or a tidal stream atlas is used to predict the direction and speed of tidal currents.
A nautical chart is a graphic representation of a sea area and adjacent coastal regions. Depending on the scale of the chart, it may show depths of water and heights of land, natural features of the seabed, details of the coastline, navigational hazards, locations of natural and human-made aids to navigation, information on tides and currents, local details of the Earth's magnetic field, and human-made structures such as harbours, buildings and bridges. Nautical charts are essential tools for marine navigation; many countries require vessels, especially commercial ships, to carry them. Nautical charting may take the form of charts printed on paper or computerized electronic navigational charts. Recent technologies have made available paper charts which are printed "on demand" with cartographic data that has been downloaded to the commercial printing company as recently as the night before printing. With each daily download, critical data such as Local Notices to Mariners are added to the on-demand chart files so that these charts are up to date at the time of printing.
Tidal power or tidal energy is a form of hydropower that converts the energy obtained from tides into useful forms of power, mainly electricity.
An amphidromic point, also called a tidal node, is a geographical location which has zero tidal amplitude for one harmonic constituent of the tide. The tidal range for that harmonic constituent increases with distance from this point.
The lunitidal interval, measures the time lag from the Moon passing overhead, to the next high or low tide. It is also called the high water interval (HWI). Sometimes a term is not used for the time lag, but instead the terms age of the tide or the establishment of the tide are used for the entry that is in the tidal tables.
HMS Conway was a naval training school or "school ship", founded in 1859 and housed for most of her life aboard a 19th-century wooden ship of the line. The ship was originally stationed on the Mersey near Liverpool, then moved to the Menai Strait during World War II. While being towed back to Birkenhead for a refit in 1953, she ran aground and was wrecked, and later burned. The school moved to purpose-built premises on Anglesey where it continued for another twenty years.
Saltstraumen is a small strait with one of the strongest tidal currents in the world. It is located in the municipality of Bodø in Nordland county, Norway. It is located about 10 kilometres (6.2 mi) southeast of the town of Bodø. The narrow channel connects the outer Saltfjorden to the large Skjerstad Fjord between the islands of Straumøya and Knaplundsøya. The Saltstraumen Bridge on Norwegian County Road 17 crosses Saltstraumen.
Slack water, also known as 'the stand of the tide', is a short period in a body of tidal water when the water is completely unstressed, and there is no movement either way in the tidal stream, and which occurs before the direction of the tidal stream reverses. Slack water can be estimated using a tidal atlas or the tidal diamond information on a nautical chart. The time of slack water, particularly in constricted waters, does not occur at high and low water, and in certain areas, such as Primera Angostura, the ebb may run for up to three hours after the water level has started to rise, and the flood may run for three hours after the water has started to fall. Thornton Lecky, writing in 1884, illustrates the phenomenon with an inland basin of infinite size, connected to the sea by a narrow mouth. Since the level of the basin is always at mean sea level, the flood in the mouth starts at half tide, and its velocity is at its greatest at the time of high water, with the strongest ebb occurring conversely at low water.
Skookumchuck Narrows is a strait forming the entrance of Sechelt Inlet on British Columbia's Sunshine Coast in Canada. Before broadening into Sechelt Inlet, all of its tidal flow together with that of Salmon Inlet and Narrows Inlet must pass through Sechelt Rapids. At peak flows, whitecaps and whirlpools form at the rapids even in calm weather. The narrows are also the site of a Skookumchuk Narrows Provincial Park.
A chart datum is the water level that depths displayed on a nautical chart are measured from. A chart datum is generally derived from some phase of the tide. Common chart datums are lowest astronomical tide and mean lower low water. In non-tidal areas, e.g., the Baltic Sea, Mean Sea Level (MSL) is used.
Tide tables, sometimes called tide charts, are used for tidal prediction and show the daily times and levels of high and low tides, usually for a particular location. Tide heights at intermediate times can be approximated by using the rule of twelfths or more accurately calculated by using a published tidal curve for the location. Tide levels are typically given relative to a low-water vertical datum, e.g. the mean lower low water (MLLW) datum in the US.
The rule of twelfths is an approximation to a sine curve. It can be used as a rule of thumb for estimating a changing quantity where both the quantity and the steps are easily divisible by 12. Typical uses are predicting the height of the tide or the change in day length over the seasons.
The River Roach is a river that flows entirely through the English county of Essex. It is one of four main streams that originate in the Rayleigh Hills to the west, and flow east. They then flow towards the centre of the Rochford Basin, a circular feature which may have been caused by an asteroid impact in the Late Oligocene or Early Miocene periods. To the east of Rochford, the river becomes tidal, and is governed by the Crouch Harbour Authority. It joins the River Crouch between Wallasea Island and Foulness Island. To the west of Rochford, there is some doubt as to which of the four streams is officially the Roach.
Dr. Arthur Thomas Doodson was a British oceanographer.
BATCO, short for Battle Code, is a hand-held, paper-based encryption system used at a low, front line level in the British Army. It was introduced along with the Clansman combat net radio in the early 1980s and was largely obsolete by 2010 due to the wide deployment of the secure Bowman radios. BATCO consists of a code, contained on a set of vocabulary cards, and cipher sheets for superencryption of the numeric code words. The cipher sheets, which are typically changed daily, also include an authentication table and a radio call sign protection system.
New Zealand has large ocean energy resources but does not yet generate any power from them. TVNZ reported in 2007 that over 20 wave and tidal power projects are currently under development. However, not a lot of public information is available about these projects. The Aotearoa Wave and Tidal Energy Association was established in 2006 to "promote the uptake of marine energy in New Zealand". According to their 10 February 2008 newsletter, they have 59 members. However, the association doesn't list its members.
Evopod is a unique tidal energy device being developed by a UK-based company Oceanflow Energy Ltd for generating electricity from tidal streams and ocean currents. It can operate in exposed deep water sites where severe wind and waves also make up the environment.
A tidal stream generator, often referred to as a tidal energy converter (TEC), is a machine that extracts energy from moving masses of water, in particular tides, although the term is often used in reference to machines designed to extract energy from run of river or tidal estuarine sites. Certain types of these machines function very much like underwater wind turbines, and are thus often referred to as tidal turbines. They were first conceived in the 1970s during the oil crisis.