The movement of the horizontal flow of the sea is called streams. These streams when related to the rise and fall of the local tide are called tidal streams. It usually flows in and out of harbour and along the coast. The tidal stream that flow into a harbour with a rising tidal is called the “ingoing tide”. The one that flow in with a falling tide is called the “outgoing tide”. When it is off-shore, they are called according to the direction in which they flow i.e. “eastgoing” or “westgoing”. Tidal streams flow fastest where the water is deeper or the channel narrower.
Causes
Tidal streams are caused in response to the tide rising forces. It’s movements are affected by current which are caused by the differences of water temperature, barometric pressure or wing and irregularities in the seabed. It does not cause any net transfer of water with its flow.
Fathom was originally a land measuring term derived from the Ango-Saxon word "faetm" meaning to embrace.
In those days, most measurements were based on average size of parts of the body, such as the hand (horses are still measured this way) or the foot (that's why 12 inches are so named).
A fathom is the average distance from fingertip to fingertip of the outstretched arms of a man — about six feet. Since a man stretches out his arms to embrace his sweetheart, Britain's Parliament declared that distance be called a "fathom" and it be a unit of measure. A fathom remains six feet.
The word was also used to describe taking the measure or "to fathom" something. Today, of course, when one is trying to figure something out, they are trying to "fathom" it.
Naval Coastal Battery is the branch of armed forces concerned with operating anti-ship artillery or fixed gun batteries in coastal fortifications. It was also used as observation posts for soldiers who guarded the harbour.
It has been held as a general rule of thumb, that one shore-based gun equalled three naval guns of the same calibre, due to the steadiness of the coastal gun which allowed for significantly higher accuracy than their sea-mounted counterparts. Land-based guns also benefited in most cases from the protection of walls or earth mounds which gave the guns an added measure of protection.
The use of coastal artillery expanded during the Age of Discoveries, in the 16th century; when a colonial power took over an overseas territory, one of their first tasks was to build a coastal fortress, both to deter rival naval powers and to subjugate the natives. The Port Siloso at Sentosa is an excellent example of a widely used coastal fort which mounted defensive artillery, in this case muzzle-loading cannon. During the 19th century China also built hundreds of coastal fortresses in an attempt to counter Western naval threats.
Three Mile Limit
The original three-mile limit was the recognized distance from a nation's shore over which that nation had jurisdiction. This border of international waters or the "high seas" was established because, at the time this international law was established, three miles was the longest range of any nation's most powerful guns, and therefore, the limit from shore batteries at which they could enforce their laws. (International law and the 1988 Territorial Sea Proclamation established the "high seas" border at the 12-mile limit.)
Manning and Cheering ship as a collective mark of respect in honour of a person or of another ship is a very old custom. In the days of sail the yards and shrouds were manned as well as the decks, but now a days only decks are manned. Some example of occasions on which this mark of honour is paid are: visit of Sovereign to the Fleet, the entry into port of ships which have shared a victory, the final departure of a ship from a foreign station on her way home to pay-off.
It is the custom for the youngest member of the ship's company to "ring out the Old Year and ring in the New" by striking 16 bells at midnight on the New Year's Eve.
Next in line, and still within the orbit of the "happy ship," comes the navigator. With the ship at sea and under way "The Pilot" seldom leaves his navigating bridge. In harbour there are his charts to correct and a number of small jobs such as checking range-finder ranges which help the gunnery officer. He also has charge of the ship's chronometers - and here again tradition steps in.
Time was when a ship's chronometer, used for determining by calculation the ship's precise longitude at any moment, were one of the most important items of her equipment. Latitude, the other geographical dimension, could always be found from the sun at noon, or the Pole-star at night; but to find the longitude necessitated a very accurate time-keeper which was never allowed to run down and of which the error on Greenwich time was known accurately to a second from day to day.
Since in the knowledge of a ship's position at sea lies the safety of the ship the responsibility for the care of and the regular winding of the chronometers was always paramount - not only for the officers, but also for the men.
And how easy it is to forget to wind a watch or a clock - we all know that, But chronometers must not be forgotten - and, moreover, they must be wound at the same time each day. So the problem of clock forgetfulness was overcome by the simple process of requiring a Colour Sergeant, to follow the navigating officer (whose duty it is to wind the chronometers) like a shadow from eight a.m. onwards until the job has been done. Once they are wound, the "shadow" reports to the captain – "Chronometers wound" - a simple report but one which, in the old days before the advent of wireless time-signals, held in its grasp the safety of all on board. Even to-day, with wireless pips" going almost every half-hour from one station or another, the tradition of safety is maintained and the report continues.
Semaphore Flags are a system for conveying information at a distance by means of visual signals with hand-held flags, rods, disks, paddles, or occasionally bare or gloved hands. Information is encoded by the position of the flags; it is read when the flag is in a fixed position. It is still used during underway replenishment at sea and is acceptable for emergency communication in daylight or, using lighted wands instead of flags, at night.
The newer flag semaphore system uses two short poles with square flags, which a signalman holds in different positions to signal letters of the alphabet and numbers. The signalman holds one pole in each hand, and extends each arm in one of eight possible directions. Except for in the rest position, the flags cannot overlap. The flags are coloured differently based on whether the signals are sent by sea or by land. At sea, the flags are coloured red and yellow (the Oscar flag), while on land, they are white and blue (the Papa flag).
A ship's displacement is its mass at any given time, generally expressed in metric tons or long tons. The term is often used to mean the ship's mass when it is loaded to its maximum capacity. A number of synonymous terms exist for this maximum mass, such as loaded displacement, full load displacement and designated displacement. Displacement is a measurement of mass, and should not be confused with similarly named measurements of volume or capacity such as net tonnage, gross tonnage, or deadweight tonnage.
The word displacement refers to the mass of the water that the ship displaces while floating. Another way of thinking about displacement is the amount of water that would spill out of a completely filled container, were the ship to be placed into it. A floating ship always displaces an amount of water of the same mass as the ship.
The density (mass per unit of volume) of water can vary. For example, the average density of seawater at the surface of the ocean is 1025 kg/m³ (10.25 lb/gallon, 8.55 lb/US gallon), fresh water on the other hand has a density of about 1000 kg/m³ (10.00 lb/ga, 8.35 lb/US gallon). Consider a 100-ton ship passing from a saltwater sea into a freshwater river. It always displaces exactly 100 tons of water, but it has to displace a greater volume of fresh water to amount to 100 tons. Therefore it would sit slightly lower in the water in the freshwater river than it would in the saltwater sea.
It can be useful to know a ship's displacement when it is unloaded or partially loaded. Terms for these measurements include light displacement, standard displacement, and normal displacement. These terms are defined fully below.
In some harbours where there is sufficient room to berth many ships alongside, ships may be obliged to berth at right-angles to a jetty, with their sterns secured to it by berthing lines and their anchors(s) laid out ahead.
This type of mooring can only be employed where there is a negligible range of tide, and is commonly used in Mediterranean ports; for this reason it is often called the Mediterranean (or Med) moor.
The major considerations are to veer sufficient cable so that the ship can swing clear of other ships at the berth when leaving, to lay the anchors sufficiently far apart to make the ship more secure in wind, and to ensure the anchors do not foul those of other ships.
In a shallow harbour it is recommended that a frigate veers about 4 shackles of cable on each anchor, and that cables are spanned with and included angle of about 50 degrees, so as to make the ship more secure in a wind. It is obvious, however, that to berth will not be safe if a gale blows from abeam.
If such weather is forecast it is advisable to put to sea or seek a sheltered anchor berth. Ships fitter with a single anchor can, in theory, carry out a Med moor; however, the single anchor will hold the bows steady only in benign weather conditions.
Hypothermia is a lowered body temperature less than 95 degrees F. Cold water near-drowning is considered a submersion accident often leading to unconsciousness or coma in water temperatures of 70 degrees F or less. A long submersion time is considered 4 to 6 minutes or greater.
Hypothermia may be mild, moderate, or severe. The presentation may range from shivering and piloerection ("goosebumps"), to profound confusion, irreversible coma and death. Significant hypothermia begins at temperatures of 95 degrees F and below. The lowering of the body temperature occurs as the body is robbed of heat by the surroundings.
Water conducts body heat away up to 26 times faster than air of the same temperature. Normal body functions slow down with decreasing heart rate, decreasing respiratory and metabolic rate. Thinking is impaired and speech becomes confused. Reflexes are slowed and muscles become stiff and unusable. Then dangerous life-threatening heart rhythms develop which are hard to reverse. Hypothermia is the opposite of hyperthermia, the condition that causes heat exhaustion and heat stroke.
Hypothermia describes a state in which the body's mechanism for temperature regulation is overwhelmed in the face of a cold stressor. All survivors should know that hypothermia is a potential killer.
The word "port hole" originated during the reign of Henry VI of England (1485). King Henry insisted on mounting guns too large for his ship and the traditional methods of securing these weapons on the forecastle and aftcastle could not be used.
A French shipbuilder named James Baker was commissioned to solve the problem. He put small doors in the side of the ship and mounted the cannon inside the ship. These doors protected the cannon from weather and were opened when the cannon were to be used. The French word for "door" is "porte" which was later Anglicized to "port" and later went on to mean any opening in the ship's side, whether for cannon or not.
Fathom was originally a land measuring term derived from the Ango-Saxon word "faetm" meaning to embrace.
In ancient days, most measurements were based on average size of parts of the body, such as the hand (horses are still measured this way) or the foot (that's why 12 inches are so named).
A fathom is the average distance from fingertip to fingertip of the outstretched arms of a man - about six feet. Since a man stretches out his arms to embrace his sweetheart, Britain's Parliament declared that distance be called a "fathom" and it be a unit of measure. A fathom remains six feet. The word was also used to describe taking the measure or "to fathom" something.
Today, of course, when one is trying to figure something out, they are trying to "fathom" it.
The Global Positioning System (GPS) is a world-wide 24 hour navigation positioning system operated by the US Department of Defence. It consists of a Ground Control Segment, a Space Segment and a User Equipment Segment. The User equipment segment is what is commonly known as a GPS receiver.
24 earth-orbiting satellites in six different orbits form the Space Segment . (There are also 3 or 4 operational spares in orbit at any one time.) Each satellite circles 10,900 nautical miles above the earth in orbits inclined at an angle of 55 degrees to the equator. Each satellite transmits precision timing signals (derived from onboard atomic clocks) on two frequencies, L1 and L2. A separate channel on each frequency is dedicated to each satellite.
The navigation messages broadcast on the L1 frequency contain two codes, one for civilian use, and another encrypted code for military use. The L2 broadcast contains a second set of navigational messages, which when combined with the encrypted code in the L1 frequency, can resolve positions to less than 20 meters. Known as the Precise Positioning Service (PPS), this service is available only to the US military, and its allies.
The non-encrypted codes in the L1 frequency, (available to civilian users), provide the Standard Positioning Service (SPS).
When GPS was in its initial testing phases it was found that this service provided position fixes that were far more accurate than was originally intended, so SPS accuracy was intentionally degraded by the introduction of random errors in the timing signal--reducing the position fixing accuracy of GPS to 100 meters 98% of the time. This intentional degradation of the timing signal was known as Selective Availability (SA), and constituted over half the total GPS error prior to May 1, 2000. (The satellite clock need only be "dithered" by a few millionths of a second to create the desired effect. That is why, in spite of SA, GPS time is the most accurate clock you will have on board your vessel.)
However, recognizing the importance of GPS to the civilian economy, the United States Government removed Selective Availability on May 1, 2000. Now the single largest contributor to GPS error is interference with the broadcast signals caused by the ionosphere (a shell of electrically charged particles that surrounds the earth.) Now a GPS position is expected to be accurate within 20 meters.
Each satellite also broadcasts "Almanac" and "Ephemeris" messages. Your earthbound GPS receiver uses the almanac to determine which satellites are above the horizon and what channels they are broadcasting on. The receiver then locks on to the most appropriate satellites for fixing a position. Given the exact time the navigation message was broadcast, and knowing the time it was received, the GPS receiver determines the amount of time it takes for the coded signal to travel from the satellite to your antenna. From there it is a simple computation to determine the actual distance between the satellite and your GPS antenna.
From this point, the GPS receiver calculates a position in the same way as a human navigator using radar ranges. The ephemeris message tells the receiver the exact location of the satellite when the message was broadcast, and since the receiver now knows the distance to the satellite, it calculates that it must be on the surface of an imaginary sphere, centered on the satellite. Where that sphere intersects with the surface of the earth, a Circle of Position ( COP) is formed.
From two satellites the receiver calculates two COP's, which cross at two possible positions. To determine which position is the correct one, a third satellite range is needed. Thus, for a receiver at sea level, a minimum of three satellites are needed to determine a two-dimensional position. For aircraft, and vehicles on land, which operate above sea level, a fourth satellite is needed to determine a three-dimensional position (including altitude).
Satellite timing signals are subject to small errors, so each orbiting satellite is closely monitored from five sites around the world (The Ground Control Segment). The main control facility at Falcon Air Force Base, Colorado, makes minor adjustments to keep the system within its prescribed limits of accuracy--(20 meters).
The procedures and practices involved in Navy ship naming are the products of evolution and tradition, rather than of legislation. In most of the navies, ships are regarded as female, while Russian ships were considered male. More recently, the US Navy has decided to defer to the Associated Press style guide, and refer to ships as "it" - a practice that may improve the post-service employment opportunities of Navy News Service writers, but that does nothing to instill a sense of tradition in the sea services.
Custom adhered to by navies in naming their ships is that a name is only repeated in a later vessel if the predecessor went out of service honourably -- through being sold to another owner, scrapped, or lost by enemy action. The name of a ship destroyed by fire or lost in collision or grounding is not repeated. It would perhaps be more appropriate to decide each case on its merits, but the custom seems quite inflexible.
