Port Hole

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.

What is Fathom ?

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.

How GPS Works

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).

Naming a ship

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.

CALCULATION OF APPROXIMATE BREAKING STRENGTH

CALCULATION OF APPROXIMATE BREAKING STRENGTH  AND SAFE WORKING LOAD  FOR MANILA ROPE

Method of finding the Breaking Strength (B.S) is to divide the square of the diameter of the rope in millimetres by 200.
Example of a diameter 24mm Manila Rope:
Breaking strength = diameter² / 200
= 24² / 200
= 576 / 200
= 2.88 tonnes (approx. 3 tonnes)

Safe Working Load (S.W.L)
Method of finding the Safe Working Load (S.W.L) is to divide the Breaking Strength by factor of safety.

The following factors of safety for ropes are used generally:
Lifts and hoist - 12
Running rigging and slings - 8
Other purposes - 6
Safe Working Load = Breaking Strength / Safety Factor
= 3 tonnes / 6
= 0.5 tonnes

CALCULATION OF APPROXIMATE BREAKING STRENGTH (B.S) AND SAFE WORKING LOAD (S.W.L) FOR POLYPROPYLENE ROPE

Method of finding the Breaking Strength (B.S) is to divide the square of the diameter of the rope in millimetres by 77 tonnes.
Example of a diameter 24mm Polypropylene Rope:
Breaking strength = diameter² / 77
= 24² / 77
= 576 / 77
= 7.48 tonnes (approx. 7 tonnes)

Method of finding the Safe Working Load (S.W.L) is to divide the Breaking Strength by a safety factor of 6.
Safe Working Load = Breaking Strength / Safety Factor
= 7 tonnes / 6
= 1.18 tonnes( approx. 1 ton)

CALCULATION OF APPROXIMATE BREAKING STRENGTH (B.S) AND SAFE WORKING LOAD (S.W.L) FOR POLYETHYLENE ROPE

Method of finding the Breaking Strength (B.S) is to divide the square of the diameter of the rope in millimetres by 106 tonnes.
Example of a diameter 24mm Polyethylene Rope:

Breaking strength = diameter² / 106
= 24² / 106
= 576 / 106
= 5.43 tonnes (approx. 5 tonnes)

Method of finding the Safe Working Load (S.W.L) is to divide the Breaking Strength by a safety factor of 6. 

Safe Working Load = Breaking Strength / Safety Factor
= 5 tonnes / 6
= .83 tonnes

Fire Ship

A fire ship, used in the days of wooden rowed or sailing ships, was a ship filled with combustibles, deliberately set on fire and steered (or, where possible, allowed to drift) into an enemy fleet, in order to destroy ships, or to create panic and make the enemy break formation. Ships used as fire ships were usually old and worn out or purpose-built inexpensive vessels.

Warships of the age of sail were highly vulnerable to fire. Made of wood, with seams caulked with tar, ropes greased with fat, and stores of gunpowder, there was little that would not burn. Accidental fires destroyed many ships, so fire ships presented a terrifying threat.

With the wind in exactly the right direction a fire ship could be cast loose and allowed to drift onto its target, but in most battles fire ships were equipped with skeleton crews to steer the ship to the target (the crew were expected to abandon ship at the last moment and escape in the ship's boat). Fire ships were most devastating against fleets which were at anchor or otherwise restricted in movement. At sea, a well-handled ship could evade a fire ship and disable it with cannon fire. 

Other tactics were to fire at the ship's boats and other vessels in the vicinity, so that the crew could not escape and therefore might decide not to ignite the ship, or to wait until the fire ship had been abandoned and then tow it aside with small maneuverable vessels. 

During the period of the Crusades their use was frequent. Their use peaked during the 18th and 19th centuries, with fireships a permanent part of any naval fleet, ready to be deployed whenever necessary, such as the Battle of Tripoli Harbor.